The patch titled
Subject: mm: fix PTE_AF handling in fault path on architectures with HW AF support
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-fix-pte_af-handling-in-fault-path-on-architectures-with-hw-af-support.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-pte_af-handling-in-fault-path-on-architectures-with-hw-af-support.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Ram Tummala <rtummala@xxxxxxxxxx>
Subject: mm: fix PTE_AF handling in fault path on architectures with HW AF support
Date: Tue, 9 Jul 2024 17:09:42 -0700
Commit 3bd786f76de2 ("mm: convert do_set_pte() to set_pte_range()")
replaced do_set_pte() with set_pte_range() and that introduced a
regression in the following faulting path of non-anonymous vmas on CPUs
with HW AF (Access Flag) support.
handle_pte_fault()
do_pte_missing()
do_fault()
do_read_fault() || do_cow_fault() || do_shared_fault()
finish_fault()
set_pte_range()
The polarity of prefault calculation is incorrect. This leads to prefault
being incorrectly set for the faulting address. The following if check
will incorrectly clear the PTE_AF bit instead of setting it and the access
will fault again on the same address due to the missing PTE_AF bit.
if (prefault && arch_wants_old_prefaulted_pte())
entry = pte_mkold(entry);
On a subsequent fault on the same address, the faulting path will see a
non NULL vmf->pte and instead of reaching the do_pte_missing() path,
PTE_AF will be correctly set in handle_pte_fault() itself.
Due to this bug, performance degradation in the fault handling path will
be observed due to unnecessary double faulting.
Link: https://lkml.kernel.org/r/20240710000942.623704-1-rtummala@xxxxxxxxxx
Fixes: 3bd786f76de2 ("mm: convert do_set_pte() to set_pte_range()")
Signed-off-by: Ram Tummala <rtummala@xxxxxxxxxx>
Reviewed-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/memory.c~mm-fix-pte_af-handling-in-fault-path-on-architectures-with-hw-af-support
+++ a/mm/memory.c
@@ -4681,7 +4681,7 @@ void set_pte_range(struct vm_fault *vmf,
{
struct vm_area_struct *vma = vmf->vma;
bool write = vmf->flags & FAULT_FLAG_WRITE;
- bool prefault = in_range(vmf->address, addr, nr * PAGE_SIZE);
+ bool prefault = !in_range(vmf->address, addr, nr * PAGE_SIZE);
pte_t entry;
flush_icache_pages(vma, page, nr);
_
Patches currently in -mm which might be from rtummala@xxxxxxxxxx are
mm-fix-pte_af-handling-in-fault-path-on-architectures-with-hw-af-support.patch
