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

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