Re: [PATCH] HWPOISON: add a pr_err message when forcibly send a sigbus

[Will Deacon]

On Sat, Aug 19, 2023 at 06:22:12PM +0800, Shuai Xue wrote:
> When a process tries to access a page that is already offline

How does this happen?

> the kernel will send a sigbus signal with the BUS_MCEERR_AR code. This
> signal is typically handled by a registered sigbus handler in the
> process. However, if the process does not have a registered sigbus
> handler, it is important for end users to be informed about what
> happened.
> 
> To address this, add an error message similar to those implemented on
> the x86, powerpc, and parisc platforms.
> 
> Signed-off-by: Shuai Xue <xueshuai@xxxxxxxxxxxxxxxxx>
> ---
>  arch/arm64/mm/fault.c  | 2 ++
>  arch/parisc/mm/fault.c | 5 ++---
>  arch/x86/mm/fault.c    | 3 +--
>  3 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 3fe516b32577..38e2186882bd 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -679,6 +679,8 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
>  	} else if (fault & (VM_FAULT_HWPOISON_LARGE | VM_FAULT_HWPOISON)) {
>  		unsigned int lsb;
>  
> +		pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
> +		       current->comm, current->pid, far);
>  		lsb = PAGE_SHIFT;
>  		if (fault & VM_FAULT_HWPOISON_LARGE)
>  			lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));

Hmm, I'm not convinced by this. We have 'show_unhandled_signals' already,
and there's plenty of code in memory-failure.c for handling poisoned pages
reported by e.g. GHES. I don't think dumping extra messages in dmesg from
the arch code really adds anything.

Will