Re: [PATCH v1 5/5] mm, hwpoison: enable memory error handling on 1GB hugepage

[Miaohe Lin <linmiaohe@huawei.com>]

On 2022/6/2 13:06, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@nec.com>
> 
> Now error handling code is prepared, so remove the blocking code and
> enable memory error handling on 1GB hugepage.
> 

I'm nervous about this change. It seems there are many code paths not awared of pud swap entry.
I browsed some of them:
apply_to_pud_range called from apply_to_page_range:

apply_to_pud_range:
	next = pud_addr_end(addr, end);
	if (pud_none(*pud) && !create)
		continue;
	if (WARN_ON_ONCE(pud_leaf(*pud)))
		return -EINVAL;
	if (!pud_none(*pud) && WARN_ON_ONCE(pud_bad(*pud))) {
		if (!create)
			continue;
		pud_clear_bad(pud);
	}
	err = apply_to_pmd_range(mm, pud, addr, next,
				 fn, data, create, mask);

For !pud_present case, it will mostly reach apply_to_pmd_range and call pmd_offset on it. And invalid
pointer will be de-referenced.

Another example might be copy_pud_range and so on. So I think it might not be prepared to enable the
1GB hugepage or all of these places should be fixed?

Thanks!

> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
> ---
>  include/linux/mm.h      |  1 -
>  include/ras/ras_event.h |  1 -
>  mm/memory-failure.c     | 16 ----------------
>  3 files changed, 18 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 04de0c3e4f9f..58a6aa916e4f 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3238,7 +3238,6 @@ enum mf_action_page_type {
>  	MF_MSG_DIFFERENT_COMPOUND,
>  	MF_MSG_HUGE,
>  	MF_MSG_FREE_HUGE,
> -	MF_MSG_NON_PMD_HUGE,
>  	MF_MSG_UNMAP_FAILED,
>  	MF_MSG_DIRTY_SWAPCACHE,
>  	MF_MSG_CLEAN_SWAPCACHE,
> diff --git a/include/ras/ras_event.h b/include/ras/ras_event.h
> index d0337a41141c..cbd3ddd7c33d 100644
> --- a/include/ras/ras_event.h
> +++ b/include/ras/ras_event.h
> @@ -360,7 +360,6 @@ TRACE_EVENT(aer_event,
>  	EM ( MF_MSG_DIFFERENT_COMPOUND, "different compound page after locking" ) \
>  	EM ( MF_MSG_HUGE, "huge page" )					\
>  	EM ( MF_MSG_FREE_HUGE, "free huge page" )			\
> -	EM ( MF_MSG_NON_PMD_HUGE, "non-pmd-sized huge page" )		\
>  	EM ( MF_MSG_UNMAP_FAILED, "unmapping failed page" )		\
>  	EM ( MF_MSG_DIRTY_SWAPCACHE, "dirty swapcache page" )		\
>  	EM ( MF_MSG_CLEAN_SWAPCACHE, "clean swapcache page" )		\
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index babeb34f7477..ced033a99e19 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -725,7 +725,6 @@ static const char * const action_page_types[] = {
>  	[MF_MSG_DIFFERENT_COMPOUND]	= "different compound page after locking",
>  	[MF_MSG_HUGE]			= "huge page",
>  	[MF_MSG_FREE_HUGE]		= "free huge page",
> -	[MF_MSG_NON_PMD_HUGE]		= "non-pmd-sized huge page",
>  	[MF_MSG_UNMAP_FAILED]		= "unmapping failed page",
>  	[MF_MSG_DIRTY_SWAPCACHE]	= "dirty swapcache page",
>  	[MF_MSG_CLEAN_SWAPCACHE]	= "clean swapcache page",
> @@ -1614,21 +1613,6 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
>  
>  	page_flags = head->flags;
>  
> -	/*
> -	 * TODO: hwpoison for pud-sized hugetlb doesn't work right now, so
> -	 * simply disable it. In order to make it work properly, we need
> -	 * make sure that:
> -	 *  - conversion of a pud that maps an error hugetlb into hwpoison
> -	 *    entry properly works, and
> -	 *  - other mm code walking over page table is aware of pud-aligned
> -	 *    hwpoison entries.
> -	 */
> -	if (huge_page_size(page_hstate(head)) > PMD_SIZE) {
> -		action_result(pfn, MF_MSG_NON_PMD_HUGE, MF_IGNORED);
> -		res = -EBUSY;
> -		goto out;
> -	}
> -
>  	if (!hwpoison_user_mappings(p, pfn, flags, head)) {
>  		action_result(pfn, MF_MSG_UNMAP_FAILED, MF_IGNORED);
>  		res = -EBUSY;
>