diff mbox series

[v2,3/7] mm/vmalloc.c: allow vread() to read out vm_map_ram areas

Message ID 20221217015435.73889-4-bhe@redhat.com
State New
Headers
Series mm/vmalloc.c: allow vread() to read out vm_map_ram areas |

Commit Message

Baoquan He Dec. 17, 2022, 1:54 a.m. UTC 
  Currently, vread can read out vmalloc areas which is associated with
a vm_struct. While this doesn't work for areas created by vm_map_ram()
interface because it doesn't have an associated vm_struct. Then in vread(),
these areas will be skipped.

Here, add a new function vb_vread() to read out areas managed by
vmap_block specifically. Then recognize vm_map_ram areas via vmap->flags
and handle them respectively.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 mm/vmalloc.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 59 insertions(+), 7 deletions(-)

Comments

kernel test robot Dec. 17, 2022, 4:10 a.m. UTC | #1 
Hi Baoquan,

I love your patch! Perhaps something to improve:

[auto build test WARNING on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/Baoquan-He/mm-vmalloc-c-allow-vread-to-read-out-vm_map_ram-areas/20221217-095615
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20221217015435.73889-4-bhe%40redhat.com
patch subject: [PATCH v2 3/7] mm/vmalloc.c: allow vread() to read out vm_map_ram areas
config: powerpc-randconfig-r031-20221216
compiler: clang version 16.0.0 (https://github.com/llvm/llvm-project 98b13979fb05f3ed288a900deb843e7b27589e58)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install powerpc cross compiling tool for clang build
        # apt-get install binutils-powerpc-linux-gnu
        # https://github.com/intel-lab-lkp/linux/commit/368cd65be8fedd1642e53393dc3f28ff8726122d
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Baoquan-He/mm-vmalloc-c-allow-vread-to-read-out-vm_map_ram-areas/20221217-095615
        git checkout 368cd65be8fedd1642e53393dc3f28ff8726122d
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=powerpc olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=powerpc SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> mm/vmalloc.c:3563:35: warning: operator '<<' has lower precedence than '-'; '-' will be evaluated first [-Wshift-op-parentheses]
                   n = (re - rs + 1) << PAGE_SHIFT - offset;
                                     ~~ ~~~~~~~~~~~^~~~~~~~
   mm/vmalloc.c:3563:35: note: place parentheses around the '-' expression to silence this warning
                   n = (re - rs + 1) << PAGE_SHIFT - offset;
                                        ~~~~~~~~~~~^~~~~~~~
   1 warning generated.


vim +3563 mm/vmalloc.c

  3533	
  3534	static void vb_vread(char *buf, char *addr, int count)
  3535	{
  3536		char *start;
  3537		struct vmap_block *vb;
  3538		unsigned long offset;
  3539		unsigned int rs, re, n;
  3540	
  3541		vb = xa_load(&vmap_blocks, addr_to_vb_idx((unsigned long)addr));
  3542	
  3543		spin_lock(&vb->lock);
  3544		if (bitmap_empty(vb->used_map, VMAP_BBMAP_BITS)) {
  3545			spin_unlock(&vb->lock);
  3546			memset(buf, 0, count);
  3547			return;
  3548		}
  3549		for_each_set_bitrange(rs, re, vb->used_map, VMAP_BBMAP_BITS) {
  3550			if (!count)
  3551				break;
  3552			start = vmap_block_vaddr(vb->va->va_start, rs);
  3553			if (addr < start) {
  3554				if (count == 0)
  3555					break;
  3556				*buf = '\0';
  3557				buf++;
  3558				addr++;
  3559				count--;
  3560			}
  3561			/*it could start reading from the middle of used region*/
  3562			offset = offset_in_page(addr);
> 3563			n = (re - rs + 1) << PAGE_SHIFT - offset;
  3564			if (n > count)
  3565				n = count;
  3566			aligned_vread(buf, start+offset, n);
  3567	
  3568			buf += n;
  3569			addr += n;
  3570			count -= n;
  3571		}
  3572		spin_unlock(&vb->lock);
  3573	
  3574		/* zero-fill the left dirty or free regions */
  3575		if (count)
  3576			memset(buf, 0, count);
  3577	}
  3578
kernel test robot Dec. 17, 2022, 6:41 a.m. UTC | #2 
Hi Baoquan,

I love your patch! Perhaps something to improve:

[auto build test WARNING on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/Baoquan-He/mm-vmalloc-c-allow-vread-to-read-out-vm_map_ram-areas/20221217-095615
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20221217015435.73889-4-bhe%40redhat.com
patch subject: [PATCH v2 3/7] mm/vmalloc.c: allow vread() to read out vm_map_ram areas
config: loongarch-randconfig-r006-20221216
compiler: loongarch64-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/368cd65be8fedd1642e53393dc3f28ff8726122d
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Baoquan-He/mm-vmalloc-c-allow-vread-to-read-out-vm_map_ram-areas/20221217-095615
        git checkout 368cd65be8fedd1642e53393dc3f28ff8726122d
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=loongarch olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=loongarch SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   mm/vmalloc.c: In function 'vb_vread':
>> mm/vmalloc.c:3563:49: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
    3563 |                 n = (re - rs + 1) << PAGE_SHIFT - offset;


vim +3563 mm/vmalloc.c

  3533	
  3534	static void vb_vread(char *buf, char *addr, int count)
  3535	{
  3536		char *start;
  3537		struct vmap_block *vb;
  3538		unsigned long offset;
  3539		unsigned int rs, re, n;
  3540	
  3541		vb = xa_load(&vmap_blocks, addr_to_vb_idx((unsigned long)addr));
  3542	
  3543		spin_lock(&vb->lock);
  3544		if (bitmap_empty(vb->used_map, VMAP_BBMAP_BITS)) {
  3545			spin_unlock(&vb->lock);
  3546			memset(buf, 0, count);
  3547			return;
  3548		}
  3549		for_each_set_bitrange(rs, re, vb->used_map, VMAP_BBMAP_BITS) {
  3550			if (!count)
  3551				break;
  3552			start = vmap_block_vaddr(vb->va->va_start, rs);
  3553			if (addr < start) {
  3554				if (count == 0)
  3555					break;
  3556				*buf = '\0';
  3557				buf++;
  3558				addr++;
  3559				count--;
  3560			}
  3561			/*it could start reading from the middle of used region*/
  3562			offset = offset_in_page(addr);
> 3563			n = (re - rs + 1) << PAGE_SHIFT - offset;
  3564			if (n > count)
  3565				n = count;
  3566			aligned_vread(buf, start+offset, n);
  3567	
  3568			buf += n;
  3569			addr += n;
  3570			count -= n;
  3571		}
  3572		spin_unlock(&vb->lock);
  3573	
  3574		/* zero-fill the left dirty or free regions */
  3575		if (count)
  3576			memset(buf, 0, count);
  3577	}
  3578
Baoquan He Dec. 17, 2022, 9:46 a.m. UTC | #3 
On 12/17/22 at 02:41pm, kernel test robot wrote:
> Hi Baoquan,
> 
> I love your patch! Perhaps something to improve:
> 
> [auto build test WARNING on akpm-mm/mm-everything]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Baoquan-He/mm-vmalloc-c-allow-vread-to-read-out-vm_map_ram-areas/20221217-095615
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
> patch link:    https://lore.kernel.org/r/20221217015435.73889-4-bhe%40redhat.com
> patch subject: [PATCH v2 3/7] mm/vmalloc.c: allow vread() to read out vm_map_ram areas
> config: loongarch-randconfig-r006-20221216
> compiler: loongarch64-linux-gcc (GCC) 12.1.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://github.com/intel-lab-lkp/linux/commit/368cd65be8fedd1642e53393dc3f28ff8726122d
>         git remote add linux-review https://github.com/intel-lab-lkp/linux
>         git fetch --no-tags linux-review Baoquan-He/mm-vmalloc-c-allow-vread-to-read-out-vm_map_ram-areas/20221217-095615
>         git checkout 368cd65be8fedd1642e53393dc3f28ff8726122d
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=loongarch olddefconfig
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=loongarch SHELL=/bin/bash
> 
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@intel.com>
> 
> All warnings (new ones prefixed by >>):
> 
>    mm/vmalloc.c: In function 'vb_vread':
> >> mm/vmalloc.c:3563:49: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
>     3563 |                 n = (re - rs + 1) << PAGE_SHIFT - offset;

Thanks, below code change can fix the warning.

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index bdaceda1b878..ec5665e70114 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3544,7 +3544,7 @@ static void vb_vread(char *buf, char *addr, int count)
 		}
 		/*it could start reading from the middle of used region*/
 		offset = offset_in_page(addr);
-		n = (re - rs + 1) << PAGE_SHIFT - offset;
+		n = ((re - rs + 1) << PAGE_SHIFT) - offset;
 		if (n > count)
 			n = count;
 		aligned_vread(buf, start+offset, n);
Lorenzo Stoakes Dec. 17, 2022, 12:06 p.m. UTC | #4 
On Sat, Dec 17, 2022 at 09:54:31AM +0800, Baoquan He wrote:
> Currently, vread can read out vmalloc areas which is associated with
> a vm_struct. While this doesn't work for areas created by vm_map_ram()
> interface because it doesn't have an associated vm_struct. Then in vread(),
> these areas will be skipped.
>
> Here, add a new function vb_vread() to read out areas managed by
> vmap_block specifically. Then recognize vm_map_ram areas via vmap->flags
> and handle them respectively.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>  mm/vmalloc.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 59 insertions(+), 7 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 190f29bbaaa7..6612914459cf 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3515,6 +3515,51 @@ static int aligned_vread(char *buf, char *addr, unsigned long count)
>  	return copied;
>  }
>
> +static void vb_vread(char *buf, char *addr, int count)
> +{
> +	char *start;
> +	struct vmap_block *vb;
> +	unsigned long offset;
> +	unsigned int rs, re, n;
> +
> +	vb = xa_load(&vmap_blocks, addr_to_vb_idx((unsigned long)addr));
> +
> +	spin_lock(&vb->lock);
> +	if (bitmap_empty(vb->used_map, VMAP_BBMAP_BITS)) {
> +		spin_unlock(&vb->lock);
> +		memset(buf, 0, count);
> +		return;
> +	}
> +	for_each_set_bitrange(rs, re, vb->used_map, VMAP_BBMAP_BITS) {
> +		if (!count)
> +			break;
> +		start = vmap_block_vaddr(vb->va->va_start, rs);
> +		if (addr < start) {
> +			if (count == 0)
> +				break;
> +			*buf = '\0';
> +			buf++;
> +			addr++;
> +			count--;
> +		}

I may be missing something here, but is this not essentially 'if the address is
below a used region, write a single null byte into the buffer and continue,
assuming we are now in a used area?'

This doesn't seem right, but I am happy to be corrected (perhaps we only expect
to be a single byte below a start region?)

> +		/*it could start reading from the middle of used region*/
> +		offset = offset_in_page(addr);
> +		n = (re - rs + 1) << PAGE_SHIFT - offset;

The kernel bot has already picked up on this paren issue :)

> +		if (n > count)
> +			n = count;
> +		aligned_vread(buf, start+offset, n);
> +
> +		buf += n;
> +		addr += n;
> +		count -= n;
> +	}
> +	spin_unlock(&vb->lock);
> +
> +	/* zero-fill the left dirty or free regions */
> +	if (count)
> +		memset(buf, 0, count);
> +}
> +
>  /**
>   * vread() - read vmalloc area in a safe way.
>   * @buf:     buffer for reading data
> @@ -3545,7 +3590,7 @@ long vread(char *buf, char *addr, unsigned long count)
>  	struct vm_struct *vm;
>  	char *vaddr, *buf_start = buf;
>  	unsigned long buflen = count;
> -	unsigned long n;
> +	unsigned long n, size, flags;
>
>  	addr = kasan_reset_tag(addr);
>
> @@ -3566,12 +3611,16 @@ long vread(char *buf, char *addr, unsigned long count)
>  		if (!count)
>  			break;
>
> -		if (!va->vm)
> +		vm = va->vm;
> +		flags = va->flags & VMAP_FLAGS_MASK;
> +
> +		if (!vm && !flags)
>  			continue;
>

This seems very delicate now as going forward, vm _could_ be NULL. In fact, a
later patch in the series then goes on to use vm and assume it is not null (will
comment).

I feel we should be very explicit after here asserting that vm != NULL.

> -		vm = va->vm;
> -		vaddr = (char *) vm->addr;
> -		if (addr >= vaddr + get_vm_area_size(vm))
> +		vaddr = (char *) va->va_start;
> +		size = flags ? va_size(va) : get_vm_area_size(vm);

For example here, I feel that this ternary should be reversed and based on
whether vm is null, unles we expect vm to ever be non-null _and_ flags to be
set?

> +
> +		if (addr >= vaddr + size)
>  			continue;
>  		while (addr < vaddr) {
>  			if (count == 0)
> @@ -3581,10 +3630,13 @@ long vread(char *buf, char *addr, unsigned long count)
>  			addr++;
>  			count--;
>  		}
> -		n = vaddr + get_vm_area_size(vm) - addr;
> +		n = vaddr + size - addr;
>  		if (n > count)
>  			n = count;
> -		if (!(vm->flags & VM_IOREMAP))
> +
> +		if ((flags & (VMAP_RAM|VMAP_BLOCK)) == (VMAP_RAM|VMAP_BLOCK))
> +			vb_vread(buf, addr, n);
> +		else if ((flags & VMAP_RAM) || !(vm->flags & VM_IOREMAP))
>  			aligned_vread(buf, addr, n);
>  		else /* IOREMAP area is treated as memory hole */
>  			memset(buf, 0, n);
> --
> 2.34.1
>
Baoquan He Jan. 4, 2023, 8:01 a.m. UTC | #5 
On 12/17/22 at 12:06pm, Lorenzo Stoakes wrote:
> On Sat, Dec 17, 2022 at 09:54:31AM +0800, Baoquan He wrote:
> > Currently, vread can read out vmalloc areas which is associated with
> > a vm_struct. While this doesn't work for areas created by vm_map_ram()
> > interface because it doesn't have an associated vm_struct. Then in vread(),
> > these areas will be skipped.
> >
> > Here, add a new function vb_vread() to read out areas managed by
> > vmap_block specifically. Then recognize vm_map_ram areas via vmap->flags
> > and handle them respectively.
> >
> > Signed-off-by: Baoquan He <bhe@redhat.com>
> > ---
> >  mm/vmalloc.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++------
> >  1 file changed, 59 insertions(+), 7 deletions(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 190f29bbaaa7..6612914459cf 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -3515,6 +3515,51 @@ static int aligned_vread(char *buf, char *addr, unsigned long count)
> >  	return copied;
> >  }
> >
> > +static void vb_vread(char *buf, char *addr, int count)
> > +{
> > +	char *start;
> > +	struct vmap_block *vb;
> > +	unsigned long offset;
> > +	unsigned int rs, re, n;
> > +
> > +	vb = xa_load(&vmap_blocks, addr_to_vb_idx((unsigned long)addr));
> > +
> > +	spin_lock(&vb->lock);
> > +	if (bitmap_empty(vb->used_map, VMAP_BBMAP_BITS)) {
> > +		spin_unlock(&vb->lock);
> > +		memset(buf, 0, count);
> > +		return;
> > +	}
> > +	for_each_set_bitrange(rs, re, vb->used_map, VMAP_BBMAP_BITS) {
> > +		if (!count)
> > +			break;
> > +		start = vmap_block_vaddr(vb->va->va_start, rs);
> > +		if (addr < start) {
> > +			if (count == 0)
> > +				break;
> > +			*buf = '\0';
> > +			buf++;
> > +			addr++;
> > +			count--;
> > +		}

Very sorry, Lorenzo, I just noticed this mail. It's very weird. Earlier,
Uladzislau's reply to patch 2/7 got to be seen in my mutt mail client 10
days later. I am not sure it's my mail client's problem, or a mail server
delivery issue.

> 
> I may be missing something here, but is this not essentially 'if the address is
> below a used region, write a single null byte into the buffer and continue,
> assuming we are now in a used area?'

Not sure if I got you. for_each_set_bitrange only iterates the used
regions. So in the for loop, what we do is fill zero into the buffer
below the used region, then read out the used region. You said
'continue', I don't understand what it means.

Assume we have 3 used regions in one vmap block, see below diagram. 
     |_______|______________|________|_____________|_____|_____________|______|
     |hole 0 |used region 0 |hole 1  |used region 1|hole2|used region2 |hole 3 |

hole 0,1,2 will be set zero when we iterate to the used region above
them. And the last hole 3 is set at the end of this function. Please
help point it out if I got it wrong.
 
> 
> This doesn't seem right, but I am happy to be corrected (perhaps we only expect
> to be a single byte below a start region?)
> 
> > +		/*it could start reading from the middle of used region*/
> > +		offset = offset_in_page(addr);
> > +		n = (re - rs + 1) << PAGE_SHIFT - offset;
> 
> The kernel bot has already picked up on this paren issue :)

Right, has been handled. Thanks.

> 
> > +		if (n > count)
> > +			n = count;
> > +		aligned_vread(buf, start+offset, n);
> > +
> > +		buf += n;
> > +		addr += n;
> > +		count -= n;
> > +	}
> > +	spin_unlock(&vb->lock);
> > +
> > +	/* zero-fill the left dirty or free regions */
> > +	if (count)
> > +		memset(buf, 0, count);
> > +}
> > +
> >  /**
> >   * vread() - read vmalloc area in a safe way.
> >   * @buf:     buffer for reading data
> > @@ -3545,7 +3590,7 @@ long vread(char *buf, char *addr, unsigned long count)
> >  	struct vm_struct *vm;
> >  	char *vaddr, *buf_start = buf;
> >  	unsigned long buflen = count;
> > -	unsigned long n;
> > +	unsigned long n, size, flags;
> >
> >  	addr = kasan_reset_tag(addr);
> >
> > @@ -3566,12 +3611,16 @@ long vread(char *buf, char *addr, unsigned long count)
> >  		if (!count)
> >  			break;
> >
> > -		if (!va->vm)
> > +		vm = va->vm;
> > +		flags = va->flags & VMAP_FLAGS_MASK;
> > +
> > +		if (!vm && !flags)
> >  			continue;
> >
> 
> This seems very delicate now as going forward, vm _could_ be NULL. In fact, a
> later patch in the series then goes on to use vm and assume it is not null (will
> comment).
> 
> I feel we should be very explicit after here asserting that vm != NULL.
> 
> > -		vm = va->vm;
> > -		vaddr = (char *) vm->addr;
> > -		if (addr >= vaddr + get_vm_area_size(vm))
> > +		vaddr = (char *) va->va_start;
> > +		size = flags ? va_size(va) : get_vm_area_size(vm);
> 
> For example here, I feel that this ternary should be reversed and based on
> whether vm is null, unles we expect vm to ever be non-null _and_ flags to be
> set?

Now only vm_map_ram area sets flags, all other types has vm not null.
Since those temporary state, e.g vm==NULL, flags==0 case has been
filtered out. Is below you suggested?

		size = (!vm&&flags)? va_size(va) : get_vm_area_size(vm);
		or
		size = (vm&&!flags)? get_vm_area_size(vm):va_size(va);

> 
> > +
> > +		if (addr >= vaddr + size)
> >  			continue;
> >  		while (addr < vaddr) {
> >  			if (count == 0)
> > @@ -3581,10 +3630,13 @@ long vread(char *buf, char *addr, unsigned long count)
> >  			addr++;
> >  			count--;
> >  		}
> > -		n = vaddr + get_vm_area_size(vm) - addr;
> > +		n = vaddr + size - addr;
> >  		if (n > count)
> >  			n = count;
> > -		if (!(vm->flags & VM_IOREMAP))
> > +
> > +		if ((flags & (VMAP_RAM|VMAP_BLOCK)) == (VMAP_RAM|VMAP_BLOCK))
> > +			vb_vread(buf, addr, n);
> > +		else if ((flags & VMAP_RAM) || !(vm->flags & VM_IOREMAP))
> >  			aligned_vread(buf, addr, n);
> >  		else /* IOREMAP area is treated as memory hole */
> >  			memset(buf, 0, n);
> > --
> > 2.34.1
> >
>
Lorenzo Stoakes Jan. 4, 2023, 8:20 p.m. UTC | #6 
On Wed, Jan 04, 2023 at 04:01:36PM +0800, Baoquan He wrote:
> On 12/17/22 at 12:06pm, Lorenzo Stoakes wrote:
> > On Sat, Dec 17, 2022 at 09:54:31AM +0800, Baoquan He wrote:
> > > Currently, vread can read out vmalloc areas which is associated with
> > > a vm_struct. While this doesn't work for areas created by vm_map_ram()
> > > interface because it doesn't have an associated vm_struct. Then in vread(),
> > > these areas will be skipped.
> > >
> > > Here, add a new function vb_vread() to read out areas managed by
> > > vmap_block specifically. Then recognize vm_map_ram areas via vmap->flags
> > > and handle them respectively.
> > >
> > > Signed-off-by: Baoquan He <bhe@redhat.com>
> > > ---
> > >  mm/vmalloc.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++------
> > >  1 file changed, 59 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > index 190f29bbaaa7..6612914459cf 100644
> > > --- a/mm/vmalloc.c
> > > +++ b/mm/vmalloc.c
> > > @@ -3515,6 +3515,51 @@ static int aligned_vread(char *buf, char *addr, unsigned long count)
> > >  	return copied;
> > >  }
> > >
> > > +static void vb_vread(char *buf, char *addr, int count)
> > > +{
> > > +	char *start;
> > > +	struct vmap_block *vb;
> > > +	unsigned long offset;
> > > +	unsigned int rs, re, n;
> > > +
> > > +	vb = xa_load(&vmap_blocks, addr_to_vb_idx((unsigned long)addr));
> > > +
> > > +	spin_lock(&vb->lock);
> > > +	if (bitmap_empty(vb->used_map, VMAP_BBMAP_BITS)) {
> > > +		spin_unlock(&vb->lock);
> > > +		memset(buf, 0, count);
> > > +		return;
> > > +	}
> > > +	for_each_set_bitrange(rs, re, vb->used_map, VMAP_BBMAP_BITS) {
> > > +		if (!count)
> > > +			break;
> > > +		start = vmap_block_vaddr(vb->va->va_start, rs);
> > > +		if (addr < start) {
> > > +			if (count == 0)
> > > +				break;
> > > +			*buf = '\0';
> > > +			buf++;
> > > +			addr++;
> > > +			count--;
> > > +		}
>
> Very sorry, Lorenzo, I just noticed this mail. It's very weird. Earlier,
> Uladzislau's reply to patch 2/7 got to be seen in my mutt mail client 10
> days later. I am not sure it's my mail client's problem, or a mail server
> delivery issue.
>

Odd, maybe try lei with mutt I find that works well :)

> >
> > I may be missing something here, but is this not essentially 'if the address is
> > below a used region, write a single null byte into the buffer and continue,
> > assuming we are now in a used area?'
>
> Not sure if I got you. for_each_set_bitrange only iterates the used
> regions. So in the for loop, what we do is fill zero into the buffer
> below the used region, then read out the used region. You said
> 'continue', I don't understand what it means.
>
> Assume we have 3 used regions in one vmap block, see below diagram.
>      |_______|______________|________|_____________|_____|_____________|______|
>      |hole 0 |used region 0 |hole 1  |used region 1|hole2|used region2 |hole 3 |
>
> hole 0,1,2 will be set zero when we iterate to the used region above
> them. And the last hole 3 is set at the end of this function. Please
> help point it out if I got it wrong.

Maybe let me rephrase:-

- We want to read `count` bytes from `addr` into `buf`
- We iterate over _used_ blocks, placing the start/end of each block in `rs`, `re`
  respectively.
- If we hit a block whose start address is above the one in which we are interested then:-
  - Place a zero byte in the buffer
  - Increment `addr` by 1 byte
  - Decrement the `count` by 1 byte
  - Carry on

I am seriously confused as to why we do this? Surely we should be checking
whether the range [addr, addr + count) overlaps this block at all, and only then
copying the relevant region?

It's the fact that blocks are at base page granularity but then this condition
is at byte granularity that is confusing to me (again it's _very_ possible I am
just being dumb here and missing something, just really want to understand this
better :)

> > > -		vm = va->vm;
> > > -		vaddr = (char *) vm->addr;
> > > -		if (addr >= vaddr + get_vm_area_size(vm))
> > > +		vaddr = (char *) va->va_start;
> > > +		size = flags ? va_size(va) : get_vm_area_size(vm);
> >
> > For example here, I feel that this ternary should be reversed and based on
> > whether vm is null, unles we expect vm to ever be non-null _and_ flags to be
> > set?
>
> Now only vm_map_ram area sets flags, all other types has vm not null.
> Since those temporary state, e.g vm==NULL, flags==0 case has been
> filtered out. Is below you suggested?
>
> 		size = (!vm&&flags)? va_size(va) : get_vm_area_size(vm);
> 		or
> 		size = (vm&&!flags)? get_vm_area_size(vm):va_size(va);
>

Sorry I didn't phrase this very well, my point is that the key thing you're
relying on here is whether vm exists in order to use it so I simply meant:-

size = vm ? get_vm_area_size(vm) : va_size(va);

This just makes it really explicit that you need vm to be non-NULL, and you've
already done the flags check before so this should suffice.
Baoquan He Jan. 9, 2023, 4:35 a.m. UTC | #7 
On 01/04/23 at 08:20pm, Lorenzo Stoakes wrote:
> On Wed, Jan 04, 2023 at 04:01:36PM +0800, Baoquan He wrote:
> > On 12/17/22 at 12:06pm, Lorenzo Stoakes wrote:
> > > On Sat, Dec 17, 2022 at 09:54:31AM +0800, Baoquan He wrote:
> > > > Currently, vread can read out vmalloc areas which is associated with
> > > > a vm_struct. While this doesn't work for areas created by vm_map_ram()
> > > > interface because it doesn't have an associated vm_struct. Then in vread(),
> > > > these areas will be skipped.
> > > >
> > > > Here, add a new function vb_vread() to read out areas managed by
> > > > vmap_block specifically. Then recognize vm_map_ram areas via vmap->flags
> > > > and handle them respectively.
> > > >
> > > > Signed-off-by: Baoquan He <bhe@redhat.com>
> > > > ---
> > > >  mm/vmalloc.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++------
> > > >  1 file changed, 59 insertions(+), 7 deletions(-)
> > > >
> > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > > index 190f29bbaaa7..6612914459cf 100644
> > > > --- a/mm/vmalloc.c
> > > > +++ b/mm/vmalloc.c
> > > > @@ -3515,6 +3515,51 @@ static int aligned_vread(char *buf, char *addr, unsigned long count)
> > > >  	return copied;
> > > >  }
> > > >
> > > > +static void vb_vread(char *buf, char *addr, int count)
> > > > +{
> > > > +	char *start;
> > > > +	struct vmap_block *vb;
> > > > +	unsigned long offset;
> > > > +	unsigned int rs, re, n;
> > > > +
> > > > +	vb = xa_load(&vmap_blocks, addr_to_vb_idx((unsigned long)addr));
> > > > +
> > > > +	spin_lock(&vb->lock);
> > > > +	if (bitmap_empty(vb->used_map, VMAP_BBMAP_BITS)) {
> > > > +		spin_unlock(&vb->lock);
> > > > +		memset(buf, 0, count);
> > > > +		return;
> > > > +	}
> > > > +	for_each_set_bitrange(rs, re, vb->used_map, VMAP_BBMAP_BITS) {
> > > > +		if (!count)
> > > > +			break;
> > > > +		start = vmap_block_vaddr(vb->va->va_start, rs);
> > > > +		if (addr < start) {
> > > > +			if (count == 0)
> > > > +				break;
> > > > +			*buf = '\0';
> > > > +			buf++;
> > > > +			addr++;
> > > > +			count--;
> > > > +		}
> >
> > Very sorry, Lorenzo, I just noticed this mail. It's very weird. Earlier,
> > Uladzislau's reply to patch 2/7 got to be seen in my mutt mail client 10
> > days later. I am not sure it's my mail client's problem, or a mail server
> > delivery issue.
> >
> 
> Odd, maybe try lei with mutt I find that works well :)

Sorry for late reply, just come back from vacation.

Lei + mutt sounds like a good idea. I relied too much on mbsync in the
past.

> 
> > >
> > > I may be missing something here, but is this not essentially 'if the address is
> > > below a used region, write a single null byte into the buffer and continue,
> > > assuming we are now in a used area?'
> >
> > Not sure if I got you. for_each_set_bitrange only iterates the used
> > regions. So in the for loop, what we do is fill zero into the buffer
> > below the used region, then read out the used region. You said
> > 'continue', I don't understand what it means.
> >
> > Assume we have 3 used regions in one vmap block, see below diagram.
> >      |_______|______________|________|_____________|_____|_____________|______|
> >      |hole 0 |used region 0 |hole 1  |used region 1|hole2|used region2 |hole 3 |
> >
> > hole 0,1,2 will be set zero when we iterate to the used region above
> > them. And the last hole 3 is set at the end of this function. Please
> > help point it out if I got it wrong.
> 
> Maybe let me rephrase:-
> 
> - We want to read `count` bytes from `addr` into `buf`
> - We iterate over _used_ blocks, placing the start/end of each block in `rs`, `re`
>   respectively.
> - If we hit a block whose start address is above the one in which we are interested then:-
>   - Place a zero byte in the buffer
>   - Increment `addr` by 1 byte
>   - Decrement the `count` by 1 byte
>   - Carry on
> 
> I am seriously confused as to why we do this? Surely we should be checking
> whether the range [addr, addr + count) overlaps this block at all, and only then
> copying the relevant region?

I guessed this could be your concern, but not very sure. That
code block is copied from vread(), and my considerations are:
1) We could starting read from any position of kcore file. /proc/kcore
is a elf file logically, it's allowed to read from anywhere, right? We
don't have to read the entire file always. So the vmap_block reading is
not necessarily page aligned. It's very similar with the empty area
filling in vread().
2) memset() is doing the byte by byte reading. We can 
change code as below. While we don't save the effort very much, and we
need introduce an extra local variable to store the value of
(start - end).

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index b054081aa66b..dce4a843a9e8 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3576,6 +3576,15 @@ static void vmap_ram_vread(char *buf, char *addr, int count, unsigned long flags
+		if (addr < start) {
+			int num = min(count, (start - add));
+			memset(buf, 0, count);
+			count -= num;
+			if (count == 0)
+				break;
+			buf -= num;
+			addr -= num;
+		}
 		/*it could start reading from the middle of used region*/
 		offset = offset_in_page(addr);
 		n = ((re - rs + 1) << PAGE_SHIFT) - offset;

void *memset(void *s, int c, size_t count)
{
        char *xs = s;
 
        while (count--)
                *xs++ = c;
        return s;
}

> 
> It's the fact that blocks are at base page granularity but then this condition
> is at byte granularity that is confusing to me (again it's _very_ possible I am
> just being dumb here and missing something, just really want to understand this
> better :)

I like this kind of reviewing with careful checking and deep thinking.
For above code block, I think it's a very great point. From my point of
view, I like the memset version better, it's easier to understand. If we
all agree, we can change it to take memset way. When I made patches,
several issues related to patches were hovering in my mind at the same
time, I did not consider this one so deeply.

> 
> > > > -		vm = va->vm;
> > > > -		vaddr = (char *) vm->addr;
> > > > -		if (addr >= vaddr + get_vm_area_size(vm))
> > > > +		vaddr = (char *) va->va_start;
> > > > +		size = flags ? va_size(va) : get_vm_area_size(vm);
> > >
> > > For example here, I feel that this ternary should be reversed and based on
> > > whether vm is null, unles we expect vm to ever be non-null _and_ flags to be
> > > set?
> >
> > Now only vm_map_ram area sets flags, all other types has vm not null.
> > Since those temporary state, e.g vm==NULL, flags==0 case has been
> > filtered out. Is below you suggested?
> >
> > 		size = (!vm&&flags)? va_size(va) : get_vm_area_size(vm);
> > 		or
> > 		size = (vm&&!flags)? get_vm_area_size(vm):va_size(va);
> >
> 
> Sorry I didn't phrase this very well, my point is that the key thing you're
> relying on here is whether vm exists in order to use it so I simply meant:-
> 
> size = vm ? get_vm_area_size(vm) : va_size(va);
> 
> This just makes it really explicit that you need vm to be non-NULL, and you've
> already done the flags check before so this should suffice.

Sounds reasonable, I will copy above line you pasted. Thanks a lot.
Lorenzo Stoakes Jan. 9, 2023, 7:12 a.m. UTC | #8 
On Mon, Jan 09, 2023 at 12:35:04PM +0800, Baoquan He wrote:
> Sorry for late reply, just come back from vacation.

Hope you had a great time! :)

>
> Lei + mutt sounds like a good idea. I relied too much on mbsync in the
> past.
>

Yeah I'm finding it works well,
https://josefbacik.github.io/kernel/2021/10/18/lei-and-b4.html is a handy guide!

[snip]
> > Maybe let me rephrase:-
> >
> > - We want to read `count` bytes from `addr` into `buf`
> > - We iterate over _used_ blocks, placing the start/end of each block in `rs`, `re`
> >   respectively.
> > - If we hit a block whose start address is above the one in which we are interested then:-
> >   - Place a zero byte in the buffer
> >   - Increment `addr` by 1 byte
> >   - Decrement the `count` by 1 byte
> >   - Carry on
> >
> > I am seriously confused as to why we do this? Surely we should be checking
> > whether the range [addr, addr + count) overlaps this block at all, and only then
> > copying the relevant region?
>
> I guessed this could be your concern, but not very sure. That
> code block is copied from vread(), and my considerations are:
> 1) We could starting read from any position of kcore file. /proc/kcore
> is a elf file logically, it's allowed to read from anywhere, right? We
> don't have to read the entire file always. So the vmap_block reading is
> not necessarily page aligned. It's very similar with the empty area
> filling in vread().
> 2) memset() is doing the byte by byte reading. We can
> change code as below. While we don't save the effort very much, and we
> need introduce an extra local variable to store the value of
> (start - end).
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index b054081aa66b..dce4a843a9e8 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3576,6 +3576,15 @@ static void vmap_ram_vread(char *buf, char *addr, int count, unsigned long flags
> +		if (addr < start) {
> +			int num = min(count, (start - add));
> +			memset(buf, 0, count);
> +			count -= num;
> +			if (count == 0)
> +				break;
> +			buf -= num;
> +			addr -= num;
> +		}
>  		/*it could start reading from the middle of used region*/
>  		offset = offset_in_page(addr);
>  		n = ((re - rs + 1) << PAGE_SHIFT) - offset;
>

The difference with vread() is that uses a while loop rather than an if clause
so operates over the whole region byte-by-byte, your original would only do this
for 1 byte so now things make a lot more sense!

This approach makes sense though I'd put the count == 0 check first and nit
'add' should be 'addr'.

I am happy with either this or a while loop instead of an if which it seems is
what the original issue was!

> void *memset(void *s, int c, size_t count)
> {
>         char *xs = s;
>
>         while (count--)
>                 *xs++ = c;
>         return s;
> }
>
> >
> > It's the fact that blocks are at base page granularity but then this condition
> > is at byte granularity that is confusing to me (again it's _very_ possible I am
> > just being dumb here and missing something, just really want to understand this
> > better :)
>
> I like this kind of reviewing with careful checking and deep thinking.
> For above code block, I think it's a very great point. From my point of
> view, I like the memset version better, it's easier to understand. If we
> all agree, we can change it to take memset way. When I made patches,
> several issues related to patches were hovering in my mind at the same
> time, I did not consider this one so deeply.
>

Thanks :) I have a particular interest in vmalloc so am happy to dive in with
reviews here!

> >
> > > > > -		vm = va->vm;
> > > > > -		vaddr = (char *) vm->addr;
> > > > > -		if (addr >= vaddr + get_vm_area_size(vm))
> > > > > +		vaddr = (char *) va->va_start;
> > > > > +		size = flags ? va_size(va) : get_vm_area_size(vm);
> > > >
> > > > For example here, I feel that this ternary should be reversed and based on
> > > > whether vm is null, unles we expect vm to ever be non-null _and_ flags to be
> > > > set?
> > >
> > > Now only vm_map_ram area sets flags, all other types has vm not null.
> > > Since those temporary state, e.g vm==NULL, flags==0 case has been
> > > filtered out. Is below you suggested?
> > >
> > > 		size = (!vm&&flags)? va_size(va) : get_vm_area_size(vm);
> > > 		or
> > > 		size = (vm&&!flags)? get_vm_area_size(vm):va_size(va);
> > >
> >
> > Sorry I didn't phrase this very well, my point is that the key thing you're
> > relying on here is whether vm exists in order to use it so I simply meant:-
> >
> > size = vm ? get_vm_area_size(vm) : va_size(va);
> >
> > This just makes it really explicit that you need vm to be non-NULL, and you've
> > already done the flags check before so this should suffice.
>
> Sounds reasonable, I will copy above line you pasted. Thanks a lot.
>

Cheers!
Baoquan He Jan. 9, 2023, 12:49 p.m. UTC | #9 
On 01/09/23 at 07:12am, Lorenzo Stoakes wrote:
> On Mon, Jan 09, 2023 at 12:35:04PM +0800, Baoquan He wrote:
> > Sorry for late reply, just come back from vacation.
> 
> Hope you had a great time! :)

Thanks.

> 
> >
> > Lei + mutt sounds like a good idea. I relied too much on mbsync in the
> > past.
> >
> 
> Yeah I'm finding it works well,
> https://josefbacik.github.io/kernel/2021/10/18/lei-and-b4.html is a handy guide!

Very helpful, will try.

> 
> [snip]
> > > Maybe let me rephrase:-
> > >
> > > - We want to read `count` bytes from `addr` into `buf`
> > > - We iterate over _used_ blocks, placing the start/end of each block in `rs`, `re`
> > >   respectively.
> > > - If we hit a block whose start address is above the one in which we are interested then:-
> > >   - Place a zero byte in the buffer
> > >   - Increment `addr` by 1 byte
> > >   - Decrement the `count` by 1 byte
> > >   - Carry on
> > >
> > > I am seriously confused as to why we do this? Surely we should be checking
> > > whether the range [addr, addr + count) overlaps this block at all, and only then
> > > copying the relevant region?
> >
> > I guessed this could be your concern, but not very sure. That
> > code block is copied from vread(), and my considerations are:
> > 1) We could starting read from any position of kcore file. /proc/kcore
> > is a elf file logically, it's allowed to read from anywhere, right? We
> > don't have to read the entire file always. So the vmap_block reading is
> > not necessarily page aligned. It's very similar with the empty area
> > filling in vread().
> > 2) memset() is doing the byte by byte reading. We can
> > change code as below. While we don't save the effort very much, and we
> > need introduce an extra local variable to store the value of
> > (start - end).
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index b054081aa66b..dce4a843a9e8 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -3576,6 +3576,15 @@ static void vmap_ram_vread(char *buf, char *addr, int count, unsigned long flags
> > +		if (addr < start) {
> > +			int num = min(count, (start - add));
> > +			memset(buf, 0, count);
> > +			count -= num;
> > +			if (count == 0)
> > +				break;
> > +			buf -= num;
> > +			addr -= num;
> > +		}
> >  		/*it could start reading from the middle of used region*/
> >  		offset = offset_in_page(addr);
> >  		n = ((re - rs + 1) << PAGE_SHIFT) - offset;
> >
> 
> The difference with vread() is that uses a while loop rather than an if clause
> so operates over the whole region byte-by-byte, your original would only do this
> for 1 byte so now things make a lot more sense!

Oops, that 'if clause' is a code bug, I finally got your point until
now, my dumb head.

> 
> This approach makes sense though I'd put the count == 0 check first and nit
> 'add' should be 'addr'.
> 
> I am happy with either this or a while loop instead of an if which it seems is
> what the original issue was!

OK, I will think again which one is more appropriate.

> 
> > void *memset(void *s, int c, size_t count)
> > {
> >         char *xs = s;
> >
> >         while (count--)
> >                 *xs++ = c;
> >         return s;
> > }
> >
> > >
> > > It's the fact that blocks are at base page granularity but then this condition
> > > is at byte granularity that is confusing to me (again it's _very_ possible I am
> > > just being dumb here and missing something, just really want to understand this
> > > better :)
> >
> > I like this kind of reviewing with careful checking and deep thinking.
> > For above code block, I think it's a very great point. From my point of
> > view, I like the memset version better, it's easier to understand. If we
> > all agree, we can change it to take memset way. When I made patches,
> > several issues related to patches were hovering in my mind at the same
> > time, I did not consider this one so deeply.
> >
> 
> Thanks :) I have a particular interest in vmalloc so am happy to dive in with
> reviews here!
> 
> > >
> > > > > > -		vm = va->vm;
> > > > > > -		vaddr = (char *) vm->addr;
> > > > > > -		if (addr >= vaddr + get_vm_area_size(vm))
> > > > > > +		vaddr = (char *) va->va_start;
> > > > > > +		size = flags ? va_size(va) : get_vm_area_size(vm);
> > > > >
> > > > > For example here, I feel that this ternary should be reversed and based on
> > > > > whether vm is null, unles we expect vm to ever be non-null _and_ flags to be
> > > > > set?
> > > >
> > > > Now only vm_map_ram area sets flags, all other types has vm not null.
> > > > Since those temporary state, e.g vm==NULL, flags==0 case has been
> > > > filtered out. Is below you suggested?
> > > >
> > > > 		size = (!vm&&flags)? va_size(va) : get_vm_area_size(vm);
> > > > 		or
> > > > 		size = (vm&&!flags)? get_vm_area_size(vm):va_size(va);
> > > >
> > >
> > > Sorry I didn't phrase this very well, my point is that the key thing you're
> > > relying on here is whether vm exists in order to use it so I simply meant:-
> > >
> > > size = vm ? get_vm_area_size(vm) : va_size(va);
> > >
> > > This just makes it really explicit that you need vm to be non-NULL, and you've
> > > already done the flags check before so this should suffice.
> >
> > Sounds reasonable, I will copy above line you pasted. Thanks a lot.

Thanks again for careful reviewing and great suggestions and findings.
diff mbox series

Patch

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 190f29bbaaa7..6612914459cf 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3515,6 +3515,51 @@  static int aligned_vread(char *buf, char *addr, unsigned long count)
 	return copied;
 }
 
+static void vb_vread(char *buf, char *addr, int count)
+{
+	char *start;
+	struct vmap_block *vb;
+	unsigned long offset;
+	unsigned int rs, re, n;
+
+	vb = xa_load(&vmap_blocks, addr_to_vb_idx((unsigned long)addr));
+
+	spin_lock(&vb->lock);
+	if (bitmap_empty(vb->used_map, VMAP_BBMAP_BITS)) {
+		spin_unlock(&vb->lock);
+		memset(buf, 0, count);
+		return;
+	}
+	for_each_set_bitrange(rs, re, vb->used_map, VMAP_BBMAP_BITS) {
+		if (!count)
+			break;
+		start = vmap_block_vaddr(vb->va->va_start, rs);
+		if (addr < start) {
+			if (count == 0)
+				break;
+			*buf = '\0';
+			buf++;
+			addr++;
+			count--;
+		}
+		/*it could start reading from the middle of used region*/
+		offset = offset_in_page(addr);
+		n = (re - rs + 1) << PAGE_SHIFT - offset;
+		if (n > count)
+			n = count;
+		aligned_vread(buf, start+offset, n);
+
+		buf += n;
+		addr += n;
+		count -= n;
+	}
+	spin_unlock(&vb->lock);
+
+	/* zero-fill the left dirty or free regions */
+	if (count)
+		memset(buf, 0, count);
+}
+
 /**
  * vread() - read vmalloc area in a safe way.
  * @buf:     buffer for reading data
@@ -3545,7 +3590,7 @@  long vread(char *buf, char *addr, unsigned long count)
 	struct vm_struct *vm;
 	char *vaddr, *buf_start = buf;
 	unsigned long buflen = count;
-	unsigned long n;
+	unsigned long n, size, flags;
 
 	addr = kasan_reset_tag(addr);
 
@@ -3566,12 +3611,16 @@  long vread(char *buf, char *addr, unsigned long count)
 		if (!count)
 			break;
 
-		if (!va->vm)
+		vm = va->vm;
+		flags = va->flags & VMAP_FLAGS_MASK;
+
+		if (!vm && !flags)
 			continue;
 
-		vm = va->vm;
-		vaddr = (char *) vm->addr;
-		if (addr >= vaddr + get_vm_area_size(vm))
+		vaddr = (char *) va->va_start;
+		size = flags ? va_size(va) : get_vm_area_size(vm);
+
+		if (addr >= vaddr + size)
 			continue;
 		while (addr < vaddr) {
 			if (count == 0)
@@ -3581,10 +3630,13 @@  long vread(char *buf, char *addr, unsigned long count)
 			addr++;
 			count--;
 		}
-		n = vaddr + get_vm_area_size(vm) - addr;
+		n = vaddr + size - addr;
 		if (n > count)
 			n = count;
-		if (!(vm->flags & VM_IOREMAP))
+
+		if ((flags & (VMAP_RAM|VMAP_BLOCK)) == (VMAP_RAM|VMAP_BLOCK))
+			vb_vread(buf, addr, n);
+		else if ((flags & VMAP_RAM) || !(vm->flags & VM_IOREMAP))
 			aligned_vread(buf, addr, n);
 		else /* IOREMAP area is treated as memory hole */
 			memset(buf, 0, n);