[-next,v8,0/2] support allocating crashkernel above 4G explicitly on riscv

  On riscv, the current crash kernel allocation logic is trying to
allocate within 32bit addressible memory region by default, if
failed, try to allocate without 4G restriction.

In need of saving DMA zone memory while allocating a relatively large
crash kernel region, allocating the reserved memory top down in
high memory, without overlapping the DMA zone, is a mature solution.
Hence this patchset introduces the parameter option crashkernel=X,[high,low].

One can reserve the crash kernel from high memory above DMA zone range
by explicitly passing "crashkernel=X,high"; or reserve a memory range
below 4G with "crashkernel=X,low". Besides, there are few rules need
to take notice:
1. "crashkernel=X,[high,low]" will be ignored if "crashkernel=size"
   is specified.
2. "crashkernel=X,low" is valid only when "crashkernel=X,high" is passed
   and there is enough memory to be allocated under 4G.
3. When allocating crashkernel above 4G and no "crashkernel=X,low" is
   specified, a 128M low memory will be allocated automatically for
   swiotlb bounce buffer.
See Documentation/admin-guide/kernel-parameters.txt for more information.

To verify loading the crashkernel, adapted kexec-tools is attached below:
https://github.com/chenjh005/kexec-tools/tree/build-test-riscv-v2

Following test cases have been performed as expected:
1) crashkernel=256M                          //low=256M
2) crashkernel=1G                            //low=1G
3) crashkernel=4G                            //high=4G, low=128M(default)
4) crashkernel=4G crashkernel=256M,high      //high=4G, low=128M(default), high is ignored
5) crashkernel=4G crashkernel=256M,low       //high=4G, low=128M(default), low is ignored
6) crashkernel=4G,high                       //high=4G, low=128M(default)
7) crashkernel=256M,low                      //low=0M, invalid
8) crashkernel=4G,high crashkernel=256M,low  //high=4G, low=256M
9) crashkernel=4G,high crashkernel=4G,low    //high=0M, low=0M, invalid
10) crashkernel=512M@0xd0000000              //low=512M
11) crashkernel=1G,high crashkernel=0M,low   //high=1G, low=0M

Changes since [v8]:
1. Rebase to newest mainline head, not modifying any code logic.

Changes since [v7]:
1. Minor refactor: move crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE
   into the !high branch when the first allocation fails. Not changing
   the result but further align with Arm64 logic, refer to Baoquan's
   comment.
2. Add test case "crashkernel=1G,high crashkernel=0M,low", the result
   also matches our expectation.

Changes since [v6]:
1. Introduce the "high" flag to mark whether "crashkernel=X,high"
   is passed. Fix the retrying logic between "crashkernel=X,high"
   case and others when the first allocation attempt fails.

Changes since [v5]:
1. Update the crashkernel allocation logic when crashkernel=X,high
   is specified. In this case, region above 4G will directly get
   reserved as crashkernel, rather than trying lower 32bit allocation
   first.

Changes since [v4]:
1. Update some imprecise code comments for cmdline parsing.

Changes since [v3]:
1. Update to print warning and return explicitly on failure when
   crashkernel=size@offset is specified. Not changing the result
   in this case but making the logic more straightforward.
2. Some minor cleanup.

Changes since [v2]:
1. Update the allocation logic to ensure the high crashkernel
   region is reserved strictly above dma32_phys_limit.
2. Clean up some minor format problems.

Chen Jiahao (2):
  riscv: kdump: Implement crashkernel=X,[high,low]
  docs: kdump: Update the crashkernel description for riscv

 .../admin-guide/kernel-parameters.txt         | 15 +--
 arch/riscv/kernel/setup.c                     |  5 +
 arch/riscv/mm/init.c                          | 93 +++++++++++++++++--
 3 files changed, 99 insertions(+), 14 deletions(-)
  

Hey,

Your $subject says -next, but the patch failed to apply to
riscv/for-next. What was the base for this patchset?

Thanks,
Conor.
  

On 2023/7/26 5:48, Conor Dooley wrote:
> Hey,
>
> Your $subject says -next, but the patch failed to apply to
> riscv/for-next. What was the base for this patchset?
>
> Thanks,
> Conor.

Hi,

My patchset was tested on current linux-next HEAD
(commit ID: 1e25dd777248, tag: next-20230725) and
it seems all ok.

Could you try applying with the base above, or
is there any problem with that base?

Thanks,
Jiahao
  

On Wed, Jul 26, 2023 at 10:20:00AM +0800, chenjiahao (C) wrote:
> 
> On 2023/7/26 5:48, Conor Dooley wrote:
> > Hey,
> > 
> > Your $subject says -next, but the patch failed to apply to
> > riscv/for-next. What was the base for this patchset?
> > 
> > Thanks,
> > Conor.
> 
> Hi,
> 
> My patchset was tested on current linux-next HEAD
> (commit ID: 1e25dd777248, tag: next-20230725) and
> it seems all ok.

> Could you try applying with the base above, or
> is there any problem with that base?

There's some difference between linux-next and riscv/for-next that
prevents the patchwork automation from applying the patches.
  

On 2023/7/26 14:45, Conor Dooley wrote:
> On Wed, Jul 26, 2023 at 10:20:00AM +0800, chenjiahao (C) wrote:
>> On 2023/7/26 5:48, Conor Dooley wrote:
>>> Hey,
>>>
>>> Your $subject says -next, but the patch failed to apply to
>>> riscv/for-next. What was the base for this patchset?
>>>
>>> Thanks,
>>> Conor.
>> Hi,
>>
>> My patchset was tested on current linux-next HEAD
>> (commit ID: 1e25dd777248, tag: next-20230725) and
>> it seems all ok.
>> Could you try applying with the base above, or
>> is there any problem with that base?
> There's some difference between linux-next and riscv/for-next that
> prevents the patchwork automation from applying the patches.

Oh, I see. There is definitely a difference, since linux-next applied
a bugfix patch b690e266dae2 ("riscv: mm: fix truncation warning on RV32")
recently, whereas riscv/for-next didn't. I have worked on a wrong base
and thanks for reminding :)

I will rebase onto riscv/for-next and post my v9 pathset soon, please
check over there.

Thanks,
Jiahao