Re: [PATCH v5 1/1] mm/memory-failure: disable unpoison once hw error happens

["HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>]

On Wed, Jun 15, 2022 at 10:00:05AM +0800, zhenwei pi wrote:
> Currently unpoison_memory(unsigned long pfn) is designed for soft
> poison(hwpoison-inject) only. Since 17fae1294ad9d, the KPTE gets
> cleared on a x86 platform once hardware memory corrupts.
> 
> Unpoisoning a hardware corrupted page puts page back buddy only,
> the kernel has a chance to access the page with *NOT PRESENT* KPTE.
> This leads BUG during accessing on the corrupted KPTE.
> 
> Suggested by David&Naoya, disable unpoison mechanism when a real HW error
> happens to avoid BUG like this:
...

> 
> Fixes: 847ce401df392 ("HWPOISON: Add unpoisoning support")
> Fixes: 17fae1294ad9d ("x86/{mce,mm}: Unmap the entire page if the whole page is affected and poisoned")
> Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
> Cc: David Hildenbrand <david@redhat.com>
> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>

Cc to stable?
I think that the current approach seems predictable to me than earlier versions,
so I can agree with sending this to stable a little more confidently.

> ---
>  Documentation/vm/hwpoison.rst |  3 ++-
>  drivers/base/memory.c         |  2 +-
>  include/linux/mm.h            |  1 +
>  mm/hwpoison-inject.c          |  2 +-
>  mm/madvise.c                  |  2 +-
>  mm/memory-failure.c           | 12 ++++++++++++
>  6 files changed, 18 insertions(+), 4 deletions(-)
> 

...

> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index b85661cbdc4a..385b5e99bfc1 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -69,6 +69,8 @@ int sysctl_memory_failure_recovery __read_mostly = 1;
>  
>  atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);
>  
> +static bool hw_memory_failure;

Could you set the initial value explicitly?  Using a default value is good,
but doing as the surrounding code do is better for consistency.  And this
variable can be updated only once, so adding __read_mostly macro is also fine.

Thanks,
Naoya Horiguchi