On Thu, Oct 7, 2021 at 9:06 AM Peter Xu <peterx@xxxxxxxxxx> wrote: > > On Wed, Oct 06, 2021 at 04:57:38PM -0700, Yang Shi wrote: > > > For example, I see that both unpoison_memory() and soft_offline_page() will > > > call it too, does it mean that we'll also set the bits e.g. even when we want > > > to inject an unpoison event too? > > > > unpoison_memory() should be not a problem since it will just bail out > > once THP is met as the comment says: > > > > /* > > * unpoison_memory() can encounter thp only when the thp is being > > * worked by memory_failure() and the page lock is not held yet. > > * In such case, we yield to memory_failure() and make unpoison fail. > > */ > > But I still think setting the subpage-hwpoison bit hides too deep there, it'll > be great we can keep get_hwpoison_page() as simple as a safe version of getting > the refcount of the page we want. Or we'd still better touch up the comment > above get_hwpoison_page() to show that side effect. > > > > > > > And I think we should set the flag for soft offline too, right? The > > I'm not familiar with either memory failure or soft offline, so far it looks > right to me. However.. > > > soft offline does set the hwpoison flag for the corrupted sub page and > > doesn't split file THP, > > .. I believe this will become not true after your patch 5, right? But THP split may fail, right? > > > so it should be captured by page fault as well. And yes for poison injection. > > One more thing: besides thp split and page free, do we need to conditionally > drop the HasHwpoisoned bit when received an unpoison event? It seems not to me, as the above comment from unpoison_memory() says unpoison can encounter thp only when the thp is being worked by memory_failure() and the page lock is not held yet. So it just bails out. In addition, unpoison just works for software injected errors, not real hardware failure. > > If my understanding is correct, we may need to scan all the subpages there, to > make sure HasHwpoisoned bit reflects the latest status for the thp in question. > > > > > But your comment reminds me that get_hwpoison_page() is just called > > when !MF_COUNT_INCREASED, so it means MADV_HWPOISON still could > > escape. This needs to be covered too. > > Right, maybe that's also a clue that we shouldn't set the new page flag within > get_hwpoison_page(), since get_hwpoison_page() is actually well coupled with > MF_COUNT_INCREASED and all of them are only about refcounting of the pages. Yeah, maybe, as long as there is not early bail out in some error handling paths. > > -- > Peter Xu >
