[merged mm-hotfixes-stable] device-dax-correct-pgoff-align-in-dax_set_mapping.patch removed from -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

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The quilt patch titled
     Subject: device-dax: correct pgoff align in dax_set_mapping()
has been removed from the -mm tree.  Its filename was
     device-dax-correct-pgoff-align-in-dax_set_mapping.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: "Kun(llfl)" <llfl@linux.alibaba.com>
Subject: device-dax: correct pgoff align in dax_set_mapping()
Date: Fri, 27 Sep 2024 15:45:09 +0800

pgoff should be aligned using ALIGN_DOWN() instead of ALIGN().  Otherwise,
vmf->address not aligned to fault_size will be aligned to the next
alignment, that can result in memory failure getting the wrong address.

It's a subtle situation that only can be observed in
page_mapped_in_vma() after the page is page fault handled by
dev_dax_huge_fault.  Generally, there is little chance to perform
page_mapped_in_vma in dev-dax's page unless in specific error injection
to the dax device to trigger an MCE - memory-failure.  In that case,
page_mapped_in_vma() will be triggered to determine which task is
accessing the failure address and kill that task in the end.


We used self-developed dax device (which is 2M aligned mapping) , to
perform error injection to random address.  It turned out that error
injected to non-2M-aligned address was causing endless MCE until panic.
Because page_mapped_in_vma() kept resulting wrong address and the task
accessing the failure address was never killed properly:


[ 3783.719419] Memory failure: 0x200c9742: recovery action for dax page: 
Recovered
[ 3784.049006] mce: Uncorrected hardware memory error in user-access at 
200c9742380
[ 3784.049190] Memory failure: 0x200c9742: recovery action for dax page: 
Recovered
[ 3784.448042] mce: Uncorrected hardware memory error in user-access at 
200c9742380
[ 3784.448186] Memory failure: 0x200c9742: recovery action for dax page: 
Recovered
[ 3784.792026] mce: Uncorrected hardware memory error in user-access at 
200c9742380
[ 3784.792179] Memory failure: 0x200c9742: recovery action for dax page: 
Recovered
[ 3785.162502] mce: Uncorrected hardware memory error in user-access at 
200c9742380
[ 3785.162633] Memory failure: 0x200c9742: recovery action for dax page: 
Recovered
[ 3785.461116] mce: Uncorrected hardware memory error in user-access at 
200c9742380
[ 3785.461247] Memory failure: 0x200c9742: recovery action for dax page: 
Recovered
[ 3785.764730] mce: Uncorrected hardware memory error in user-access at 
200c9742380
[ 3785.764859] Memory failure: 0x200c9742: recovery action for dax page: 
Recovered
[ 3786.042128] mce: Uncorrected hardware memory error in user-access at 
200c9742380
[ 3786.042259] Memory failure: 0x200c9742: recovery action for dax page: 
Recovered
[ 3786.464293] mce: Uncorrected hardware memory error in user-access at 
200c9742380
[ 3786.464423] Memory failure: 0x200c9742: recovery action for dax page: 
Recovered
[ 3786.818090] mce: Uncorrected hardware memory error in user-access at 
200c9742380
[ 3786.818217] Memory failure: 0x200c9742: recovery action for dax page: 
Recovered
[ 3787.085297] mce: Uncorrected hardware memory error in user-access at 
200c9742380
[ 3787.085424] Memory failure: 0x200c9742: recovery action for dax page: 
Recovered

It took us several weeks to pinpoint this problem,  but we eventually
used bpftrace to trace the page fault and mce address and successfully
identified the issue.


Joao added:

; Likely we never reproduce in production because we always pin
: device-dax regions in the region align they provide (Qemu does
: similarly with prealloc in hugetlb/file backed memory).  I think this
: bug requires that we touch *unpinned* device-dax regions unaligned to
: the device-dax selected alignment (page size i.e.  4K/2M/1G)

Link: https://lkml.kernel.org/r/23c02a03e8d666fef11bbe13e85c69c8b4ca0624.1727421694.git.llfl@linux.alibaba.com
Fixes: b9b5777f09be ("device-dax: use ALIGN() for determining pgoff")
Signed-off-by: Kun(llfl) <llfl@linux.alibaba.com>
Tested-by: JianXiong Zhao <zhaojianxiong.zjx@alibaba-inc.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/dax/device.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/dax/device.c~device-dax-correct-pgoff-align-in-dax_set_mapping
+++ a/drivers/dax/device.c
@@ -86,7 +86,7 @@ static void dax_set_mapping(struct vm_fa
 		nr_pages = 1;
 
 	pgoff = linear_page_index(vmf->vma,
-			ALIGN(vmf->address, fault_size));
+			ALIGN_DOWN(vmf->address, fault_size));
 
 	for (i = 0; i < nr_pages; i++) {
 		struct page *page = pfn_to_page(pfn_t_to_pfn(pfn) + i);
_

Patches currently in -mm which might be from llfl@linux.alibaba.com are