Messages in this thread | | | Date | Wed, 1 Feb 2023 09:23:27 +0800 | Subject | Re: [PATCH -next resend v3] mm: hwposion: support recovery from ksm_might_need_to_copy() | From | Kefeng Wang <> |
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On 2022/12/17 10:24, Miaohe Lin wrote: > On 2022/12/16 9:47, HORIGUCHI NAOYA(堀口 直也) wrote: >> On Tue, Dec 13, 2022 at 08:05:23PM +0800, Kefeng Wang wrote: >>> When the kernel copy a page from ksm_might_need_to_copy(), but runs >>> into an uncorrectable error, it will crash since poisoned page is >>> consumed by kernel, this is similar to Copy-on-write poison recovery, >> >> Maybe you mean "this is similar to the issue recently fixed by >> Copy-on-write poison recovery."? And if this sentence ends here, >> please put "." instead of ",". >> >>> When an error is detected during the page copy, return VM_FAULT_HWPOISON >>> in do_swap_page(), and install a hwpoison entry in unuse_pte() when >>> swapoff, which help us to avoid system crash. Note, memory failure on >>> a KSM page will be skipped, but still call memory_failure_queue() to >>> be consistent with general memory failure process. >> >> Thank you for the work. I have a few comment below ... > > Thanks both. > >>> - if (unlikely(!PageUptodate(page))) { >>> - pte_t pteval; >>> + if (hwposioned || !PageUptodate(page)) { >>> + swp_entry_t swp_entry; >>> >>> dec_mm_counter(vma->vm_mm, MM_SWAPENTS); >>> - pteval = swp_entry_to_pte(make_swapin_error_entry()); >>> - set_pte_at(vma->vm_mm, addr, pte, pteval); >>> - swap_free(entry); >>> + if (hwposioned) { >>> + swp_entry = make_hwpoison_entry(swapcache); >>> + page = swapcache; >> >> This might work for the process accessing to the broken page, but ksm >> pages are likely to be shared by multiple processes, so it would be >> much nicer if you can convert all mapping entries for the error ksm page >> into hwpoisoned ones. Maybe in this thorough approach, >> hwpoison_user_mappings() is updated to call try_to_unmap() for ksm pages. >> But it's not necessary to do this together with applying mcsafe-memcpy, >> because recovery action and mcsafe-memcpy can be done independently. >> > > I'm afraid leaving the ksm page in the cache will repeatedly trigger uncorrectable error for the > same page if ksm pages are shared by multiple processes. This might reach the hardware threshold > and result in fatal uncorrectable error (thus casuing system to panic). So IMHO it might be better > to check if page is hwpoisoned before calling ksm_might_need_to_copy() if above thorough approach > is not implemented. But I can easily be wrong. > Oh,missing this one,there are only two caller, one in do_swap_page(), it has already check whether the page is hwpoisoned or not, another is in unuse_pte() which only called from swapoff, it is not a hot patch, so I don't think it is an urgent requirement. Thanks.
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