On Tue, Sep 19, 2023 at 10:21:27AM +0800, Shuai Xue wrote:
Hardware errors could be signaled by synchronous interrupt, e.g. when an error is detected by a background scrubber, or signaled by synchronous exception, e.g. when an uncorrected error is consumed. Both synchronous and asynchronous error are queued and handled by a dedicated kthread in workqueue.
commit 7f17b4a121d0 ("ACPI: APEI: Kick the memory_failure() queue for synchronous errors") keep track of whether memory_failure() work was queued, and make task_work pending to flush out the workqueue so that the work for synchronous error is processed before returning to user-space. The trick ensures that the corrupted page is unmapped and poisoned. And after returning to user-space, the task starts at current instruction which triggering a page fault in which kernel will send SIGBUS to current process due to VM_FAULT_HWPOISON.
However, the memory failure recovery for hwpoison-aware mechanisms does not work as expected. For example, hwpoison-aware user-space processes like QEMU register their customized SIGBUS handler and enable early kill mode by seting PF_MCE_EARLY at initialization. Then the kernel will directy notify the process by sending a SIGBUS signal in memory failure with wrong si_code: the actual user-space process accessing the corrupt memory location, but its memory failure work is handled in a kthread context, so it will send SIGBUS with BUS_MCEERR_AO si_code to the actual user-space process instead of BUS_MCEERR_AR in kill_proc().
To this end, separate synchronous and asynchronous error handling into different paths like X86 platform does:
- valid synchronous errors: queue a task_work to synchronously send SIGBUS before ret_to_user.
- valid asynchronous errors: queue a work into workqueue to asynchronously handle memory failure.
- abnormal branches such as invalid PA, unexpected severity, no memory failure config support, invalid GUID section, OOM, etc.
Then for valid synchronous errors, the current context in memory failure is exactly belongs to the task consuming poison data and it will send SIBBUS with proper si_code.
Fixes: 7f17b4a121d0 ("ACPI: APEI: Kick the memory_failure() queue for synchronous errors") Signed-off-by: Shuai Xue xueshuai@linux.alibaba.com Tested-by: Ma Wupeng mawupeng1@huawei.com Reviewed-by: Kefeng Wang wangkefeng.wang@huawei.com Reviewed-by: Xiaofei Tan tanxiaofei@huawei.com Reviewed-by: Baolin Wang baolin.wang@linux.alibaba.com
arch/x86/kernel/cpu/mce/core.c | 9 +--- drivers/acpi/apei/ghes.c | 84 +++++++++++++++++++++------------- include/acpi/ghes.h | 3 -- mm/memory-failure.c | 17 ++----- 4 files changed, 56 insertions(+), 57 deletions(-)
...
diff --git a/mm/memory-failure.c b/mm/memory-failure.c index 4d6e43c88489..80e1ea1cc56d 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -2163,7 +2163,9 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
- Return: 0 for successfully handled the memory error,
-EOPNOTSUPP for hwpoison_filter() filtered the error event,
< 0(except -EOPNOTSUPP) on failure.
-EHWPOISON for already sent SIGBUS to the current process with
the proper error info,
The meaning of this comment is understood, but the sentence seems to be a little too long. Could you sort this out with bullet points (like below)?
* Return values: * 0 - success * -EOPNOTSUPP - hwpoison_filter() filtered the error event. * -EHWPOISON - sent SIGBUS to the current process with the proper * error info by kill_accessing_process(). * other negative values - failure
*/
other negative error code on failure.int memory_failure(unsigned long pfn, int flags) { @@ -2445,19 +2447,6 @@ static void memory_failure_work_func(struct work_struct *work) } } -/*
- Process memory_failure work queued on the specified CPU.
- Used to avoid return-to-userspace racing with the memory_failure workqueue.
- */
-void memory_failure_queue_kick(int cpu) -{
- struct memory_failure_cpu *mf_cpu;
- mf_cpu = &per_cpu(memory_failure_cpu, cpu);
- cancel_work_sync(&mf_cpu->work);
- memory_failure_work_func(&mf_cpu->work);
-}
The declaration of memory_failure_queue_kick() still remains in include/linux/mm.h, so you can remove it together.
Thanks, Naoya Horiguchi