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SubjectRe: [PATCH v5 2/2] ACPI: APEI: handle synchronous exceptions in task work
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On 2023/4/11 18:48, 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>
> ---
> drivers/acpi/apei/ghes.c | 91 +++++++++++++++++++++++++++-------------
> include/acpi/ghes.h | 3 --
> mm/memory-failure.c | 13 ------
> 3 files changed, 61 insertions(+), 46 deletions(-)
>
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index c479b85899f5..4b70955e25f9 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -452,28 +452,51 @@ 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 sync_task_work - for synchronous RAS event
> + *
> + * @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 void ghes_kick_task_work(struct callback_head *head)
> +struct sync_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;
> + int ret;
> + struct sync_task_work *twcb =
> + container_of(twork, struct sync_task_work, twork);
>
> - 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);
> + kfree(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)
> + return;
> +
> + /*
> + * -EHWPOISON from memory_failure() means that it already sent SIGBUS
> + * to the current process with the proper error info,

This should be part of the comments of function memory_failure(),

> + * -EOPNOTSUPP means hwpoison_filter() filtered the error event,
> + *
and this part is already there
> + * In both cases, no further processing is required.
> + */
so, after that, I think we could drop this comment, also the same
comment in x86's kill_me_maybe().

> + if (ret == -EHWPOISON || ret == -EOPNOTSUPP)
> + return;
> +
> + pr_err("Memory error not recovered");
> + force_sig(SIGBUS);
> }
>
> static bool ghes_do_memory_failure(u64 physical_addr, int flags)
> {
> unsigned long pfn;
> + struct sync_task_work *twcb;
>
> if (!IS_ENABLED(CONFIG_ACPI_APEI_MEMORY_FAILURE))
> return false;
> @@ -486,6 +509,18 @@ static bool ghes_do_memory_failure(u64 physical_addr, int flags)
> return false;
> }
>
> + if (flags == MF_ACTION_REQUIRED && current->mm) {
> + twcb = kmalloc(sizeof(*twcb), GFP_ATOMIC);
> + if (!twcb)
> + return false;
> +
> + twcb->pfn = pfn;
> + twcb->flags = flags;
> + init_task_work(&twcb->twork, memory_failure_cb);
> + task_work_add(current, &twcb->twork, TWA_RESUME);
> + return true;
> + }
> +
> memory_failure_queue(pfn, flags);
> return true;
> }
> @@ -1000,9 +1035,8 @@ static void ghes_proc_in_irq(struct irq_work *irq_work)
> struct ghes_estatus_node *estatus_node;
> struct acpi_hest_generic *generic;
> struct acpi_hest_generic_status *estatus;
> - bool task_work_pending;
> + bool queued, sync;
> u32 len, node_len;
> - int ret;
>
> llnode = llist_del_all(&ghes_estatus_llist);
> /*
> @@ -1015,27 +1049,25 @@ static void ghes_proc_in_irq(struct irq_work *irq_work)
> estatus_node = llist_entry(llnode, struct ghes_estatus_node,
> llnode);
> estatus = GHES_ESTATUS_FROM_NODE(estatus_node);
> + sync = is_hest_sync_notify(estatus_node->ghes);
> len = cper_estatus_len(estatus);
> node_len = GHES_ESTATUS_NODE_LEN(len);
> - task_work_pending = ghes_do_proc(estatus_node->ghes, estatus);
> +
> + queued = ghes_do_proc(estatus_node->ghes, estatus) > + /*
> + * If no memory failure work is queued for abnormal synchronous
> + * errors, do a force kill.
> + */
> + if (sync && !queued)
> + force_sig(SIGBUS);

It's better to move this part into function ghes_do_proc(), because
there is already an is_hest_sync_notify(), and no need return value,
so make ghes_do_proc() a void function, Apart from this,

Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>

> +
> if (!ghes_estatus_cached(estatus)) {
> generic = estatus_node->generic;
> if (ghes_print_estatus(NULL, generic, estatus))
> ghes_estatus_cache_add(generic, estatus);
> }
> -
> - if (task_work_pending && current->mm) {
> - estatus_node->task_work.func = ghes_kick_task_work;
> - estatus_node->task_work_cpu = smp_processor_id();
> - ret = task_work_add(current, &estatus_node->task_work,
> - TWA_RESUME);
> - if (ret)
> - estatus_node->task_work.func = NULL;
> - }
> -
> - if (!estatus_node->task_work.func)
> - gen_pool_free(ghes_estatus_pool,
> - (unsigned long)estatus_node, node_len);
> + gen_pool_free(ghes_estatus_pool, (unsigned long)estatus_node,
> + node_len);
>
> llnode = next;
> }
> @@ -1096,7 +1128,6 @@ static int ghes_in_nmi_queue_one_entry(struct ghes *ghes,
>
> estatus_node->ghes = ghes;
> estatus_node->generic = ghes->generic;
> - estatus_node->task_work.func = NULL;
> estatus = GHES_ESTATUS_FROM_NODE(estatus_node);
>
> if (__ghes_read_estatus(estatus, buf_paddr, fixmap_idx, len)) {
> diff --git a/include/acpi/ghes.h b/include/acpi/ghes.h
> index 3c8bba9f1114..e5e0c308d27f 100644
> --- a/include/acpi/ghes.h
> +++ b/include/acpi/ghes.h
> @@ -35,9 +35,6 @@ struct ghes_estatus_node {
> struct llist_node llnode;
> struct acpi_hest_generic *generic;
> struct ghes *ghes;
> -
> - int task_work_cpu;
> - struct callback_head task_work;
> };
>
> struct ghes_estatus_cache {
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index fae9baf3be16..6ea8c325acb3 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2355,19 +2355,6 @@ 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);
> -}
> -
> static int __init memory_failure_init(void)
> {
> struct memory_failure_cpu *mf_cpu;

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