Re: [PATCH v14 3/3] ACPI: APEI: handle synchronous exceptions in task work

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在 2024/10/25 22:40, Jarkko Sakkinen 写道:
On Tue Oct 22, 2024 at 4:11 AM EEST, Shuai Xue wrote:
Hi, Jarkko,


在 2024/10/14 16:42, Shuai Xue 写道:
The memory uncorrected error could be signaled by asynchronous interrupt
(specifically, SPI in arm64 platform), e.g. when an error is detected by
a background scrubber, or signaled by synchronous exception
(specifically, data abort excepction in arm64 platform), e.g. when a CPU
tries to access a poisoned cache line. Currently, both synchronous and
asynchronous error use memory_failure_queue() to schedule
memory_failure() exectute in kworker context.

As a result, when a user-space process is accessing a poisoned data, a
data abort is taken and the memory_failure() is executed in the kworker
context:

    - will send wrong si_code by SIGBUS signal in early_kill mode, and
    - can not kill the user-space in some cases resulting a synchronous
      error infinite loop

Issue 1: send wrong si_code in early_kill mode

Since commit a70297d22132 ("ACPI: APEI: set memory failure flags as
MF_ACTION_REQUIRED on synchronous events")', the flag MF_ACTION_REQUIRED
could be used to determine whether a synchronous exception occurs on
ARM64 platform.  When a synchronous exception is detected, the kernel is
expected to terminate the current process which has accessed poisoned
page. This is done by sending a SIGBUS signal with an error code
BUS_MCEERR_AR, indicating an action-required machine check error on
read.

However, when kill_proc() is called to terminate the processes who have
the poisoned page mapped, it sends the incorrect SIGBUS error code
BUS_MCEERR_AO because the context in which it operates is not the one
where the error was triggered.

To reproduce this problem:

    #sysctl -w vm.memory_failure_early_kill=1
    vm.memory_failure_early_kill = 1

    # STEP2: inject an UCE error and consume it to trigger a synchronous error
    #einj_mem_uc single
    0: single   vaddr = 0xffffb0d75400 paddr = 4092d55b400
    injecting ...
    triggering ...
    signal 7 code 5 addr 0xffffb0d75000
    page not present
    Test passed

The si_code (code 5) from einj_mem_uc indicates that it is BUS_MCEERR_AO
error and it is not fact.

After this patch:

    # STEP1: enable early kill mode
    #sysctl -w vm.memory_failure_early_kill=1
    vm.memory_failure_early_kill = 1
    # STEP2: inject an UCE error and consume it to trigger a synchronous error
    #einj_mem_uc single
    0: single   vaddr = 0xffffb0d75400 paddr = 4092d55b400
    injecting ...
    triggering ...
    signal 7 code 4 addr 0xffffb0d75000
    page not present
    Test passed

The si_code (code 4) from einj_mem_uc indicates that it is BUS_MCEERR_AR
error as we expected.

Issue 2: a synchronous error infinite loop

If a user-space process, e.g. devmem, a poisoned page which has been set
HWPosion flag, kill_accessing_process() is called to send SIGBUS to the
current processs with error info. Because the memory_failure() is
executed in the kworker contex, it will just do nothing but return
EFAULT. So, devmem will access the posioned page and trigger an
excepction again, resulting in a synchronous error infinite loop. Such
loop may cause platform firmware to exceed some threshold and reboot
when Linux could have recovered from this error.

To reproduce this problem:

    # STEP 1: inject an UCE error, and kernel will set HWPosion flag for related page
    #einj_mem_uc single
    0: single   vaddr = 0xffffb0d75400 paddr = 4092d55b400
    injecting ...
    triggering ...
    signal 7 code 4 addr 0xffffb0d75000
    page not present
    Test passed

    # STEP 2: access the same page and it will trigger a synchronous error infinite loop
    devmem 0x4092d55b400

To fix above two issues, queue memory_failure() as a task_work so that it runs in
the context of the process that is actually consuming the poisoned data.

Signed-off-by: Shuai Xue <xueshuai@xxxxxxxxxxxxxxxxx>
Tested-by: Ma Wupeng <mawupeng1@xxxxxxxxxx>
Reviewed-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Reviewed-by: Xiaofei Tan <tanxiaofei@xxxxxxxxxx>
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
   drivers/acpi/apei/ghes.c | 78 +++++++++++++++++++++++-----------------
   include/acpi/ghes.h      |  3 --
   include/linux/mm.h       |  1 -
   mm/memory-failure.c      | 13 -------
   4 files changed, 45 insertions(+), 50 deletions(-)

diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
index f2ee28c44d7a..95e9520eb803 100644
--- a/drivers/acpi/apei/ghes.c
+++ b/drivers/acpi/apei/ghes.c
@@ -467,28 +467,42 @@ static void ghes_clear_estatus(struct ghes *ghes,
   }
/*
- * Called as task_work before returning to user-space.
- * Ensure any queued work has been done before we return to the context that
- * triggered the notification.
+ * struct ghes_task_work - for synchronous RAS event
+ *
+ * @twork:                callback_head for task work
+ * @pfn:                  page frame number of corrupted page
+ * @flags:                work control flags
+ *
+ * Structure to pass task work to be handled before
+ * returning to user-space via task_work_add().
    */


Do you have any futer comments about this patch? Any comments are
welcomed. If not, are you happy to explictly give the reveiwed-by tag?

Sorry I've been busy switching to a new job.

I read this now through and both commit messages and the code changes
look sane to me so I guess I don't have any problem with that:

Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>


Best Regard,
Shuai

BR, Jarkko


Thank you.

BR. Shuai





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