Re: [PATCH v17 3/3] ACPI: APEI: handle synchronous exceptions in task work
From: Yazen Ghannam <yazen.ghannam@amd.com>
Date: 2024-12-18 16:53:47
Also in:
linux-acpi, linux-edac, linux-mm, lkml
On Mon, Dec 02, 2024 at 11:05:27AM +0800, Shuai Xue wrote:
quoted hunk ↗ jump to hunk
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 exception 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() to exectute in a 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, memory_failure(): - 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 the 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 a BUS_MCEERR_AR error as we expected. Issue 2: a synchronous error infinite loop If a user-space process, e.g. devmem, accesses a poisoned page for which the HWPoison flag is set, kill_accessing_process() is called to send SIGBUS to current processs with error info. Because the memory_failure() is executed in the kworker context, it will just do nothing but return EFAULT. So, devmem will access the posioned page and trigger an exception again, resulting in a synchronous error infinite loop. Such exception 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@linux.alibaba.com> Tested-by: Ma Wupeng <redacted> Reviewed-by: Kefeng Wang <redacted> Reviewed-by: Xiaofei Tan <redacted> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> --- drivers/acpi/apei/ghes.c | 77 +++++++++++++++++++++++----------------- include/acpi/ghes.h | 3 -- include/linux/mm.h | 1 - mm/memory-failure.c | 13 ------- 4 files changed, 44 insertions(+), 50 deletions(-)diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c index 106486bdfefc..70f2ee3ad1a8 100644 --- a/drivers/acpi/apei/ghes.c +++ b/drivers/acpi/apei/ghes.c@@ -467,28 +467,41 @@ static void ghes_clear_estatus(struct ghes *ghes, } /*
The "kernel-doc" format needs an opening "/**".
- * 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().
*/
-static void ghes_kick_task_work(struct callback_head *head)
+struct ghes_task_work {
+ struct callback_head twork;
+ u64 pfn;
+ int flags;
+};
+
+static void memory_failure_cb(struct callback_head *twork)
{
- struct acpi_hest_generic_status *estatus;
- struct ghes_estatus_node *estatus_node;
- u32 node_len;
+ struct ghes_task_work *twcb = container_of(twork, struct ghes_task_work, twork);
+ int ret;
- estatus_node = container_of(head, struct ghes_estatus_node, task_work);
- if (IS_ENABLED(CONFIG_ACPI_APEI_MEMORY_FAILURE))
- memory_failure_queue_kick(estatus_node->task_work_cpu);
+ ret = memory_failure(twcb->pfn, twcb->flags);
+ gen_pool_free(ghes_estatus_pool, (unsigned long)twcb, sizeof(*twcb));
- estatus = GHES_ESTATUS_FROM_NODE(estatus_node);
- node_len = GHES_ESTATUS_NODE_LEN(cper_estatus_len(estatus));
- gen_pool_free(ghes_estatus_pool, (unsigned long)estatus_node, node_len);
+ if (!ret || ret == -EHWPOISON || ret == -EOPNOTSUPP)
+ return;
+
+ pr_err("%#llx: Sending SIGBUS to %s:%d due to hardware memory corruption\n",
+ twcb->pfn, current->comm, task_pid_nr(current));This is basically the same as the message in kill_proc(). Was there any consideration to have a shared function? Maybe this could be a future patch.
+ force_sig(SIGBUS);
}
static bool ghes_do_memory_failure(u64 physical_addr, int flags)
{
unsigned long pfn;
+ struct ghes_task_work *twcb;Minor nit: A common preference I've seen is to order variable declarations from longest->shortest line length. But overall, looks okay to me. Reviewed-by: Yazen Ghannam <yazen.ghannam@amd.com> Thanks, Yazen