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From:   Naoya Horiguchi <nao.horiguchi@gmail.com>
To:     linux-mm@kvack.org, Tony Luck <tony.luck@intel.com>,
        Aili Yao <yaoaili@kingsoft.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>,
        David Hildenbrand <david@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        Jue Wang <juew@google.com>, linux-kernel@vger.kernel.org
Subject: [PATCH v3 2/3] mm,hwpoison: return -EHWPOISON when page already
Date:   Wed, 21 Apr 2021 09:57:27 +0900
Message-Id: <20210421005728.1994268-3-nao.horiguchi@gmail.com>
In-Reply-To: <20210421005728.1994268-1-nao.horiguchi@gmail.com>
References: <20210421005728.1994268-1-nao.horiguchi@gmail.com>
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From: Aili Yao <yaoaili@kingsoft.com>

When the page is already poisoned, another memory_failure() call in the
same page now returns 0, meaning OK. For nested memory mce handling, this
behavior may lead to one mce looping, Example:

1. When LCME is enabled, and there are two processes A && B running on
different core X && Y separately, which will access one same page, then
the page corrupted when process A access it, a MCE will be rasied to
core X and the error process is just underway.

2. Then B access the page and trigger another MCE to core Y, it will also
do error process, it will see TestSetPageHWPoison be true, and 0 is
returned.

3. The kill_me_maybe will check the return:

    1244 static void kill_me_maybe(struct callback_head *cb)
    1245 {
    ...
    1254         if (!memory_failure(p->mce_addr >> PAGE_SHIFT, flags) &&
    1255             !(p->mce_kflags & MCE_IN_KERNEL_COPYIN)) {
    1256                 set_mce_nospec(p->mce_addr >> PAGE_SHIFT, p->mce_whole_page);
    1257                 sync_core();
    1258                 return;
    1259         }
    ...
    1267 }

4. The error process for B will end, and may nothing happened if
kill-early is not set, The process B will re-excute instruction and get
into mce again and then loop happens. And also the set_mce_nospec()
here is not proper, may refer to commit fd0e786d9d09 ("x86/mm,
mm/hwpoison: Don't unconditionally unmap kernel 1:1 pages").

For other cases which care the return value of memory_failure() should
check why they want to process a memory error which have already been
processed. This behavior seems reasonable.

Signed-off-by: Aili Yao <yaoaili@kingsoft.com>
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
---
 mm/memory-failure.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git v5.12-rc8/mm/memory-failure.c v5.12-rc8_patched/mm/memory-failure.c
index 4087308e4b32..39d0ff0339b9 100644
--- v5.12-rc8/mm/memory-failure.c
+++ v5.12-rc8_patched/mm/memory-failure.c
@@ -1228,7 +1228,7 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
 	if (TestSetPageHWPoison(head)) {
 		pr_err("Memory failure: %#lx: already hardware poisoned\n",
 		       pfn);
-		return 0;
+		return -EHWPOISON;
 	}
 
 	num_poisoned_pages_inc();
@@ -1437,6 +1437,7 @@ int memory_failure(unsigned long pfn, int flags)
 	if (TestSetPageHWPoison(p)) {
 		pr_err("Memory failure: %#lx: already hardware poisoned\n",
 			pfn);
+		res = -EHWPOISON;
 		goto unlock_mutex;
 	}
 
-- 
2.25.1