diff mbox series

mm: huge_memory: don't force huge page alignment on 32 bit

Message ID 20240118133504.2910955-1-shy828301@gmail.com
State New
Headers
Series mm: huge_memory: don't force huge page alignment on 32 bit |

Commit Message

Yang Shi Jan. 18, 2024, 1:35 p.m. UTC 
  From: Yang Shi <yang@os.amperecomputing.com>

The commit efa7df3e3bb5 ("mm: align larger anonymous mappings on THP
boundaries") caused two issues [1] [2] reported on 32 bit system or compat
userspace.

It doesn't make too much sense to force huge page alignment on 32 bit
system due to the constrained virtual address space.

[1] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#mf211643a0427f8d6495b5b53f8132f453d60ab95
[2] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#me93dff2ccbd9902c3e395e1c022fb454e48ecb1d

Fixes: efa7df3e3bb5 ("mm: align larger anonymous mappings on THP boundaries")
Reported-by: Jiri Slaby <jirislaby@kernel.org>
Reported-by: Suren Baghdasaryan <surenb@google.com>
Tested-by: Jiri Slaby <jirislaby@kernel.org>
Tested-by: Suren Baghdasaryan <surenb@google.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Christopher Lameter <cl@linux.com>
Signed-off-by: Yang Shi <yang@os.amperecomputing.com>
---
 mm/huge_memory.c | 9 +++++++++
 1 file changed, 9 insertions(+)

Comments

Matthew Wilcox Jan. 18, 2024, 8:14 p.m. UTC | #1 
On Thu, Jan 18, 2024 at 05:35:04AM -0800, Yang Shi wrote:
> It doesn't make too much sense to force huge page alignment on 32 bit
> system due to the constrained virtual address space.
> 
> [1] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#mf211643a0427f8d6495b5b53f8132f453d60ab95
> [2] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#me93dff2ccbd9902c3e395e1c022fb454e48ecb1d

I feel sure there are shorter URLs for those messages ...

> @@ -811,6 +812,14 @@ static unsigned long __thp_get_unmapped_area(struct file *filp,
>  	loff_t off_align = round_up(off, size);
>  	unsigned long len_pad, ret;
>  
> +	/*
> +	 * It doesn't make too much sense to froce huge page alignment on
> +	 * 32 bit system or compat userspace due to the contrained virtual
> +	 * address space and address entropy.
> +	 */

I honestly wouldn't even comment this.  But if you must,

	/* Using THP alignment is not as important as address randomisation */

> +	if (IS_ENABLED(CONFIG_32BIT) || in_compat_syscall())
> +		return 0;
> +
>  	if (off_end <= off_align || (off_end - off_align) < size)
>  		return 0;
>  
> -- 
> 2.41.0
>
Yang Shi Jan. 18, 2024, 8:39 p.m. UTC | #2 
On Thu, Jan 18, 2024 at 12:14 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Thu, Jan 18, 2024 at 05:35:04AM -0800, Yang Shi wrote:
> > It doesn't make too much sense to force huge page alignment on 32 bit
> > system due to the constrained virtual address space.
> >
> > [1] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#mf211643a0427f8d6495b5b53f8132f453d60ab95
> > [2] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#me93dff2ccbd9902c3e395e1c022fb454e48ecb1d
>
> I feel sure there are shorter URLs for those messages ...

Oh, yeah, I just found.

[1] https://lore.kernel.org/linux-mm/d0a136a0-4a31-46bc-adf4-2db109a61672@kernel.org/
[2] https://lore.kernel.org/linux-mm/CAJuCfpHXLdQy1a2B6xN2d7quTYwg2OoZseYPZTRpU0eHHKD-sQ@mail.gmail.com/

>
> > @@ -811,6 +812,14 @@ static unsigned long __thp_get_unmapped_area(struct file *filp,
> >       loff_t off_align = round_up(off, size);
> >       unsigned long len_pad, ret;
> >
> > +     /*
> > +      * It doesn't make too much sense to froce huge page alignment on
> > +      * 32 bit system or compat userspace due to the contrained virtual
> > +      * address space and address entropy.
> > +      */
>
> I honestly wouldn't even comment this.  But if you must,
>
>         /* Using THP alignment is not as important as address randomisation */

It is not only about address randomization. Removing the comment is fine too.

>
> > +     if (IS_ENABLED(CONFIG_32BIT) || in_compat_syscall())
> > +             return 0;
> > +
> >       if (off_end <= off_align || (off_end - off_align) < size)
> >               return 0;
> >
> > --
> > 2.41.0
> >
Michal Hocko Jan. 25, 2024, 8:53 a.m. UTC | #3 
On Thu 18-01-24 05:35:04, Yang Shi wrote:
> From: Yang Shi <yang@os.amperecomputing.com>
> 
> The commit efa7df3e3bb5 ("mm: align larger anonymous mappings on THP
> boundaries") caused two issues [1] [2] reported on 32 bit system or compat
> userspace.
> 
> It doesn't make too much sense to force huge page alignment on 32 bit
> system due to the constrained virtual address space.
> 
> [1] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#mf211643a0427f8d6495b5b53f8132f453d60ab95
> [2] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#me93dff2ccbd9902c3e395e1c022fb454e48ecb1d
> 
> Fixes: efa7df3e3bb5 ("mm: align larger anonymous mappings on THP boundaries")
> Reported-by: Jiri Slaby <jirislaby@kernel.org>
> Reported-by: Suren Baghdasaryan <surenb@google.com>
> Tested-by: Jiri Slaby <jirislaby@kernel.org>
> Tested-by: Suren Baghdasaryan <surenb@google.com>
> Cc: Rik van Riel <riel@surriel.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Christopher Lameter <cl@linux.com>
> Signed-off-by: Yang Shi <yang@os.amperecomputing.com>

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
>  mm/huge_memory.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 94ef5c02b459..e9fbaccbe0c0 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -37,6 +37,7 @@
>  #include <linux/page_owner.h>
>  #include <linux/sched/sysctl.h>
>  #include <linux/memory-tiers.h>
> +#include <linux/compat.h>
>  
>  #include <asm/tlb.h>
>  #include <asm/pgalloc.h>
> @@ -811,6 +812,14 @@ static unsigned long __thp_get_unmapped_area(struct file *filp,
>  	loff_t off_align = round_up(off, size);
>  	unsigned long len_pad, ret;
>  
> +	/*
> +	 * It doesn't make too much sense to froce huge page alignment on
> +	 * 32 bit system or compat userspace due to the contrained virtual
> +	 * address space and address entropy.
> +	 */
> +	if (IS_ENABLED(CONFIG_32BIT) || in_compat_syscall())
> +		return 0;
> +
>  	if (off_end <= off_align || (off_end - off_align) < size)
>  		return 0;
>  
> -- 
> 2.41.0
>
Michal Hocko Jan. 26, 2024, 10:51 a.m. UTC | #4 
On Fri 26-01-24 10:41:49, Jiri Slaby wrote:
> On 26. 01. 24, 10:36, Jiri Slaby wrote:
> > > > --- a/mm/huge_memory.c
> > > > +++ b/mm/huge_memory.c
> > > > @@ -37,6 +37,7 @@
> > > >   #include <linux/page_owner.h>
> > > >   #include <linux/sched/sysctl.h>
> > > >   #include <linux/memory-tiers.h>
> > > > +#include <linux/compat.h>
> > > >   #include <asm/tlb.h>
> > > >   #include <asm/pgalloc.h>
> > > > @@ -811,6 +812,14 @@ static unsigned long
> > > > __thp_get_unmapped_area(struct file *filp,
> > > >       loff_t off_align = round_up(off, size);
> > > >       unsigned long len_pad, ret;
> > > > +    /*
> > > > +     * It doesn't make too much sense to froce huge page alignment on
> > > > +     * 32 bit system or compat userspace due to the contrained virtual
> > > > +     * address space and address entropy.
> > > > +     */
> > 
> > FWIW,
> > Bernhard noticed that "froce" and "contrained", could you fix that
> > before applying the patch?
> 
> No, you can't:
> 
> 1) it was merged to mm-stable already, and
> 2) the comment is not in that version at all [1]
> 
> [1] https://lore.kernel.org/all/20240126075612.87780C433F1@smtp.kernel.org/

Matthew has objected that the comment is not really necessary and I
think he is quite right. If anything the commend would be helpful to
explain why this doesn't make much sense (because that breaks ASLR
on default configuration and compat tasks). But that should be clear
from the changelog so I think we are good here.
Greg KH Feb. 18, 2024, 9:26 a.m. UTC | #5 
On Mon, Feb 12, 2024 at 02:45:04PM +0100, Thorsten Leemhuis wrote:
> Hey Greg, is below mail still in your queue of linux-stable mails to
> process? If so please apologize this interruption and just ignore this
> mail. I just started to wonder if it might have fallen through the
> cracks somehow, as I've seen you updating stable-queue.git for 6.7.y,
> but it's still missing this patch (and the other one mentioned) --
> that's why I decided to write this quick status inquiry.

Yes, my queue is quite large because of travel and the CNA/CVE work that
was happening, am catching up now.  I've queued these up now, thanks.

greg k-h
diff mbox series

Patch

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 94ef5c02b459..e9fbaccbe0c0 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -37,6 +37,7 @@ 
 #include <linux/page_owner.h>
 #include <linux/sched/sysctl.h>
 #include <linux/memory-tiers.h>
+#include <linux/compat.h>
 
 #include <asm/tlb.h>
 #include <asm/pgalloc.h>
@@ -811,6 +812,14 @@  static unsigned long __thp_get_unmapped_area(struct file *filp,
 	loff_t off_align = round_up(off, size);
 	unsigned long len_pad, ret;
 
+	/*
+	 * It doesn't make too much sense to froce huge page alignment on
+	 * 32 bit system or compat userspace due to the contrained virtual
+	 * address space and address entropy.
+	 */
+	if (IS_ENABLED(CONFIG_32BIT) || in_compat_syscall())
+		return 0;
+
 	if (off_end <= off_align || (off_end - off_align) < size)
 		return 0;