From: Aili Yao yaoaili@kingsoft.com Subject: mm,hwpoison: return -EHWPOISON to denote that the page has already been poisoned

When memory_failure() is called with MF_ACTION_REQUIRED on the page that has already been hwpoisoned, memory_failure() could fail to send SIGBUS to the affected process, which results in infinite loop of MCEs.

Currently memory_failure() returns 0 if it's called for already hwpoisoned page, then the caller, kill_me_maybe(), could return without sending SIGBUS to current process. An action required MCE is raised when the current process accesses to the broken memory, so no SIGBUS means that the current process continues to run and access to the error page again soon, so running into MCE loop.

This issue can arise for example in the following scenarios:

- Two or more threads access to the poisoned page concurrently. If local MCE is enabled, MCE handler independently handles the MCE events. So there's a race among MCE events, and the second or latter threads fall into the situation in question.

- If there was a precedent memory error event and memory_failure() for the event failed to unmap the error page for some reason, the subsequent memory access to the error page triggers the MCE loop situation.

To fix the issue, make memory_failure() return an error code when the error page has already been hwpoisoned. This allows memory error handler to control how it sends signals to userspace. And make sure that any process touching a hwpoisoned page should get a SIGBUS even in "already hwpoisoned" path of memory_failure() as is done in page fault path.

Link: https://lkml.kernel.org/r/20210521030156.2612074-3-nao.horiguchi@gmail.com Signed-off-by: Aili Yao yaoaili@kingsoft.com Signed-off-by: Naoya Horiguchi naoya.horiguchi@nec.com Reviewed-by: Oscar Salvador osalvador@suse.de Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Petkov bp@alien8.de Cc: Borislav Petkov bp@suse.de Cc: David Hildenbrand david@redhat.com Cc: Jue Wang juew@google.com Cc: Tony Luck tony.luck@intel.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/memory-failure.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/memory-failure.c~mmhwpoison-return-ehwpoison-to-denote-that-the-page-has-already-been-poisoned +++ a/mm/memory-failure.c @@ -1253,7 +1253,7 @@ static int memory_failure_hugetlb(unsign if (TestSetPageHWPoison(head)) { pr_err("Memory failure: %#lx: already hardware poisoned\n", pfn); - return 0; + return -EHWPOISON; }

num_poisoned_pages_inc(); @@ -1461,6 +1461,7 @@ try_again: if (TestSetPageHWPoison(p)) { pr_err("Memory failure: %#lx: already hardware poisoned\n", pfn); + res = -EHWPOISON; goto unlock_mutex; }

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