Re: [PATCH v4 0/2] Copy-on-write poison recovery

Re: [PATCH v4 0/2] Copy-on-write poison recovery

[Albert E. Davies]

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[PATCH v3 0/2] Copy-on-write poison recovery

[Tony Luck]

Part 1 deals with the process that triggered the copy on write
fault with a store to a shared read-only page. That process is
send a SIGBUS with the usual machine check decoration to specify
the virtual address of the lost page, together with the scope.

Part 2 sets up to asynchronously take the page with the uncorrected
error offline to prevent additional machine check faults. H/t to
Miaohe Lin <linmiaohe@huawei.com> and Shuai Xue <xueshuai@linux.alibaba.com>
for pointing me to the existing function to queue a call to
memory_failure().

On x86 there is some duplicate reporting (because the error is
also signalled by the memory controller as well as by the core
that triggered the machine check). Console logs look like this:

[ 1647.723403] mce: [Hardware Error]: Machine check events logged
	Machine check from kernel copy routine

[ 1647.723414] MCE: Killing einj_mem_uc:3600 due to hardware memory corruption fault at 7f3309503400
	x86 fault handler sends SIGBUS to child process

[ 1647.735183] Memory failure: 0x905b92d: recovery action for dirty LRU page: Recovered
	Async call to memory_failure() from copy on write path

[ 1647.748397] Memory failure: 0x905b92d: already hardware poisoned
	uc_decode_notifier() processes memory controller report

[ 1647.761313] MCE: Killing einj_mem_uc:3599 due to hardware memory corruption fault at 7f3309503400
	Parent process tries to read poisoned page. Page has been unmapped, so
	#PF handler sends SIGBUS


Tony Luck (2):
  mm, hwpoison: Try to recover from copy-on write faults
  mm, hwpoison: When copy-on-write hits poison, take page offline

 include/linux/highmem.h | 24 ++++++++++++++++++++++++
 include/linux/mm.h      |  5 ++++-
 mm/memory.c             | 32 ++++++++++++++++++++++----------
 3 files changed, 50 insertions(+), 11 deletions(-)

-- 
2.37.3

[PATCH v4 0/2] Copy-on-write poison recovery

[Tony Luck]

Recover from poison consumption while copying pages
in the kernel for a copy-on-write fault.

Changes since v3:

1) Miaohe Lin <linmiaohe@huawei.com> pointed out that a recent change
by Alexander Potapenko <glider@google.com> to copy_user_highpage()
added a call to kmsan_unpoison_memory().  Same is needed in my cloned
copy_mc_user_highpage() ... at least in the successful case where the
page was copied with no machine checks.

2) Picked up some additional Reviewed-by and Tested-by tags.

Tony Luck (2):
  mm, hwpoison: Try to recover from copy-on write faults
  mm, hwpoison: When copy-on-write hits poison, take page offline

 include/linux/highmem.h | 26 ++++++++++++++++++++++++++
 include/linux/mm.h      |  5 ++++-
 mm/memory.c             | 32 ++++++++++++++++++++++----------
 3 files changed, 52 insertions(+), 11 deletions(-)


base-commit: 30a0b95b1335e12efef89dd78518ed3e4a71a763
-- 
2.37.3