Re: [PATCH] x86/mce: set MCE_IN_KERNEL_COPYIN for all MC-Safe Copy

[Kefeng Wang]

Hi Tony and all x86 maintainers, kindly ping, thanks.

On 2023/5/8 10:22, Kefeng Wang wrote:
> Both EX_TYPE_FAULT_MCE_SAFE and EX_TYPE_DEFAULT_MCE_SAFE exception
> fixup types are used to identify fixups which allow in kernel #MC
> recovery, that is the Machine Check Safe Copy.
>
> For now, the MCE_IN_KERNEL_COPYIN flag is only set for EX_TYPE_COPY
> and EX_TYPE_UACCESS when copy from user, and corrupted page is
> isolated in this case, for MC-safe copy, memory_failure() is not
> always called, some places, like __wp_page_copy_user, copy_subpage,
> copy_user_gigantic_page and ksm_might_need_to_copy manually call
> memory_failure_queue() to cope with such unhandled error pages,
> recently coredump hwposion recovery support[1] is asked to do the
> same thing, and there are some other already existed MC-safe copy
> scenarios, eg, nvdimm, dm-writecache, dax, which has similar issue.
>
> The best way to fix them is set MCE_IN_KERNEL_COPYIN to MCE_SAFE
> exception, then kill_me_never() will be queued to call memory_failure()
> in do_machine_check() to isolate corrupted page, which avoid calling
> memory_failure_queue() after every MC-safe copy return.
>
> [1] https://lkml.kernel.org/r/20230417045323.11054-1-wangkefeng.wang@xxxxxxxxxx
>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> ---
>   arch/x86/kernel/cpu/mce/severity.c |  3 +--
>   mm/ksm.c                           |  1 -
>   mm/memory.c                        | 12 +++---------
>   3 files changed, 4 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c
> index c4477162c07d..63e94484c5d6 100644
> --- a/arch/x86/kernel/cpu/mce/severity.c
> +++ b/arch/x86/kernel/cpu/mce/severity.c
> @@ -293,12 +293,11 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs)
>   	case EX_TYPE_COPY:
>   		if (!copy_user)
>   			return IN_KERNEL;
> -		m->kflags |= MCE_IN_KERNEL_COPYIN;
>   		fallthrough;
>   
>   	case EX_TYPE_FAULT_MCE_SAFE:
>   	case EX_TYPE_DEFAULT_MCE_SAFE:
> -		m->kflags |= MCE_IN_KERNEL_RECOV;
> +		m->kflags |= MCE_IN_KERNEL_RECOV | MCE_IN_KERNEL_COPYIN;
>   		return IN_KERNEL_RECOV;
>   
>   	default:
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 0156bded3a66..7abdf4892387 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -2794,7 +2794,6 @@ struct page *ksm_might_need_to_copy(struct page *page,
>   	if (new_page) {
>   		if (copy_mc_user_highpage(new_page, page, address, vma)) {
>   			put_page(new_page);
> -			memory_failure_queue(page_to_pfn(page), 0);
>   			return ERR_PTR(-EHWPOISON);
>   		}
>   		SetPageDirty(new_page);
> diff --git a/mm/memory.c b/mm/memory.c
> index 5e2c6b1fc00e..c0f586257017 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2814,10 +2814,8 @@ static inline int __wp_page_copy_user(struct page *dst, struct page *src,
>   	unsigned long addr = vmf->address;
>   
>   	if (likely(src)) {
> -		if (copy_mc_user_highpage(dst, src, addr, vma)) {
> -			memory_failure_queue(page_to_pfn(src), 0);
> +		if (copy_mc_user_highpage(dst, src, addr, vma))
>   			return -EHWPOISON;
> -		}
>   		return 0;
>   	}
>   
> @@ -5852,10 +5850,8 @@ static int copy_user_gigantic_page(struct folio *dst, struct folio *src,
>   
>   		cond_resched();
>   		if (copy_mc_user_highpage(dst_page, src_page,
> -					  addr + i*PAGE_SIZE, vma)) {
> -			memory_failure_queue(page_to_pfn(src_page), 0);
> +					  addr + i*PAGE_SIZE, vma))
>   			return -EHWPOISON;
> -		}
>   	}
>   	return 0;
>   }
> @@ -5871,10 +5867,8 @@ static int copy_subpage(unsigned long addr, int idx, void *arg)
>   	struct copy_subpage_arg *copy_arg = arg;
>   
>   	if (copy_mc_user_highpage(copy_arg->dst + idx, copy_arg->src + idx,
> -				  addr, copy_arg->vma)) {
> -		memory_failure_queue(page_to_pfn(copy_arg->src + idx), 0);
> +				  addr, copy_arg->vma))
>   		return -EHWPOISON;
> -	}
>   	return 0;
>   }
>