On Mon, Feb 27, 2023 at 01:03:15PM +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:
>
> - task work for synchronous errors.
> - and workqueue for asynchronous errors.
>
> Then for 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@xxxxxxxxxxxxxxxxx>
...
>
> /*
> - * 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 mce_task_work - for synchronous RAS event
This seems to handle synchronous memory errors, not limited to MCE?
So naming this struct as such (more generally) might be better.
> + *
> + * @twork: callback_head for task work
> + * @pfn: page frame number of corrupted page
> + * @flags: fine tune action taken
> + *
> + * Structure to pass task work to be handled before
> + * ret_to_user via task_work_add().
> */
...
> }
>
> -static bool ghes_do_memory_failure(u64 physical_addr, int flags)
> +static void ghes_do_memory_failure(u64 physical_addr, int flags)
> {
> unsigned long pfn;
> + struct mce_task_work *twcb;
>
> if (!IS_ENABLED(CONFIG_ACPI_APEI_MEMORY_FAILURE))
> - return false;
> + return;
>
> pfn = PHYS_PFN(physical_addr);
> if (!pfn_valid(pfn) && !arch_is_platform_page(physical_addr)) {
> pr_warn_ratelimited(FW_WARN GHES_PFX
> "Invalid address in generic error data: %#llx\n",
> physical_addr);
> - return false;
> + return;
> + }
> +
> + if (flags == MF_ACTION_REQUIRED && current->mm) {
> + twcb = kmalloc(sizeof(*twcb), GFP_ATOMIC);
> + if (!twcb)
> + return;
When this kmalloc() fails, the error event might be silently dropped?
If so, some warning messages could be helpful.
Thanks,
Naoya Horiguchi
> +
> + twcb->pfn = pfn;
> + twcb->flags = flags;
> + init_task_work(&twcb->twork, memory_failure_cb);
> + task_work_add(current, &twcb->twork, TWA_RESUME);
> + return;
> }
>
> memory_failure_queue(pfn, flags);
