[PATCH v12 3/3] ACPI: APEI: handle synchronous exceptions in task work

Shuai Xue
2024-09-02T03:00:54Z

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:

# 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 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.

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

After this patch set:

# 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 due to memory_failure() failed

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 it, if memory_failure() failed, perform a force kill to current process.

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>
---
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 b0b20ee533d9..b956e9ed020f 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 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 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 task_work *twcb = container_of(twork, struct task_work, twork);
+ unsigned long pfn = twcb->pfn;
+ 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("%#lx: Sending SIGBUS to %s:%d due to hardware memory corruption\n",
+ pfn, current->comm, task_pid_nr(current));
+ force_sig(SIGBUS);
}

static bool ghes_do_memory_failure(u64 physical_addr, int flags)
{
unsigned long pfn;
+ struct task_work *twcb;

if (!IS_ENABLED(CONFIG_ACPI_APEI_MEMORY_FAILURE))
return false;
@@ -501,6 +515,18 @@ static bool ghes_do_memory_failure(u64 physical_addr, int flags)
return false;
}

+ if (flags == MF_ACTION_REQUIRED && current->mm) {
+ twcb = (void *)gen_pool_alloc(ghes_estatus_pool, sizeof(*twcb));
+ 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;
}
@@ -745,7 +771,7 @@ int cxl_cper_kfifo_get(struct cxl_cper_work_data *wd)
}
EXPORT_SYMBOL_NS_GPL(cxl_cper_kfifo_get, CXL);

-static bool ghes_do_proc(struct ghes *ghes,
+static void ghes_do_proc(struct ghes *ghes,
const struct acpi_hest_generic_status *estatus)
{
int sev, sec_sev;
@@ -810,8 +836,6 @@ static bool ghes_do_proc(struct ghes *ghes,
current->comm, task_pid_nr(current));
force_sig(SIGBUS);
}
-
- return queued;
}

static void __ghes_print_estatus(const char *pfx,
@@ -1113,9 +1137,7 @@ 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;
u32 len, node_len;
- int ret;

llnode = llist_del_all(&ghes_estatus_llist);
/*
@@ -1130,25 +1152,16 @@ static void ghes_proc_in_irq(struct irq_work *irq_work)
estatus = GHES_ESTATUS_FROM_NODE(estatus_node);
len = cper_estatus_len(estatus);
node_len = GHES_ESTATUS_NODE_LEN(len);
- task_work_pending = ghes_do_proc(estatus_node->ghes, estatus);
+
+ ghes_do_proc(estatus_node->ghes, estatus);
+
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;
}
@@ -1209,7 +1222,6 @@ 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 be1dd4c1a917..ebd21b05fe6e 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/include/linux/mm.h b/include/linux/mm.h
index 6549d0979b28..f5f1d6a8a07d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3981,7 +3981,6 @@ enum mf_flags {
int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
unsigned long count, int mf_flags);
extern int memory_failure(unsigned long pfn, int flags);
-extern void memory_failure_queue_kick(int cpu);
extern int unpoison_memory(unsigned long pfn);
extern atomic_long_t num_poisoned_pages __read_mostly;
extern int soft_offline_page(unsigned long pfn, int flags);
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index df26e2ff5e06..e369aae2da1f 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2486,19 +2486,6 @@ 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;
--
2.39.3