[PATCH v7 22/25] ACPI / APEI: Kick the memory_failure() queue for synchronous errors

[James Morse <james.morse@arm.com>]

memory_failure() offlines or repairs pages of memory that have been
discovered to be corrupt. These may be detected by an external
component, (e.g. the memory controller), and notified via an IRQ.
In this case the work is queued as not all of memory_failure()s work
can happen in IRQ context.

If the error was detected as a result of user-space accessing a
corrupt memory location the CPU may take an abort instead. On arm64
this is a 'synchronous external abort', and on a firmware first
system it is replayed using NOTIFY_SEA.

This notification has NMI like properties, (it can interrupt
IRQ-masked code), so the memory_failure() work is queued. If we
return to user-space before the queued memory_failure() work is
processed, we will take the fault again. This loop may cause platform
firmware to exceed some threshold and reboot when Linux could have
recovered from this error.

If a ghes notification type indicates that it may be triggered again
when we return to user-space, use the task-work and notify-resume
hooks to kick the relevant memory_failure() queue before returning
to user-space.

Signed-off-by: James Morse <james.morse@arm.com>

---
current->mm == &init_mm ? I couldn't find a helper for this.
The intent is not to set TIF flags on kernel threads. What happens
if a kernel-thread takes on of these? Its just one of the many
not-handled-very-well cases we have already, as memory_failure()
puts it: "try to be lucky".

I assume that if NOTIFY_NMI is coming from SMM it must suffer from
this problem too.
---
 drivers/acpi/apei/ghes.c | 65 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 60 insertions(+), 5 deletions(-)

diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
index 6cbf9471b2a2..3e7da9243153 100644
--- a/drivers/acpi/apei/ghes.c
+++ b/drivers/acpi/apei/ghes.c
@@ -47,6 +47,7 @@
 #include <linux/sched/clock.h>
 #include <linux/uuid.h>
 #include <linux/ras.h>
+#include <linux/task_work.h>
 
 #include <acpi/actbl1.h>
 #include <acpi/ghes.h>
@@ -136,6 +137,26 @@ static atomic_t ghes_estatus_cache_alloced;
 
 static int ghes_panic_timeout __read_mostly = 30;
 
+static bool ghes_is_synchronous(struct ghes *ghes)
+{
+	switch (ghes->generic->notify.type) {
+	case ACPI_HEST_NOTIFY_NMI:	/* fall through */
+	case ACPI_HEST_NOTIFY_SEA:
+		/*
+		 * These notifications could be repeated if the interrupted
+		 * instruction is run again. e.g. a read of bad-memory causing
+		 * a trap to platform firmware.
+		 */
+		return true;
+	default:
+		/*
+		 * Other notifications are asynchronous, and not related to the
+		 * interrupted instruction. e.g. an IRQ.
+		 */
+		return false;
+	}
+}
+
 static void __iomem *ghes_map(u64 pfn, int fixmap_idx)
 {
 	phys_addr_t paddr;
@@ -379,14 +400,33 @@ static void ghes_clear_estatus(struct acpi_hest_generic_status *estatus,
 				      fixmap_idx);
 }
 
-static void ghes_handle_memory_failure(struct acpi_hest_generic_data *gdata, int sev)
+struct ghes_memory_failure_work {
+	int cpu;
+	struct callback_head work;
+};
+
+static void ghes_kick_memory_failure(struct callback_head *head)
+{
+	struct ghes_memory_failure_work *callback;
+
+	callback = container_of(head, struct ghes_memory_failure_work, work);
+	memory_failure_queue_kick(callback->cpu);
+	kfree(callback);
+}
+
+static void ghes_handle_memory_failure(struct ghes *ghes,
+				       struct acpi_hest_generic_data *gdata,
+				       int sev)
 {
-#ifdef CONFIG_ACPI_APEI_MEMORY_FAILURE
 	unsigned long pfn;
-	int flags = -1;
+	int flags = -1, ret;
+	struct ghes_memory_failure_work	*callback;
 	int sec_sev = ghes_severity(gdata->error_severity);
 	struct cper_sec_mem_err *mem_err = acpi_hest_get_payload(gdata);
 
+	if (!IS_ENABLED(CONFIG_ACPI_APEI_MEMORY_FAILURE))
+		return;
+
 	if (!(mem_err->validation_bits & CPER_MEM_VALID_PA))
 		return;
 
@@ -407,7 +447,22 @@ static void ghes_handle_memory_failure(struct acpi_hest_generic_data *gdata, int
 
 	if (flags != -1)
 		memory_failure_queue(pfn, flags);
-#endif
+
+	/*
+	 * If the notification indicates that it was the interrupted
+	 * instruction that caused the error, try to kick the
+	 * memory_failure() queue before returning to user-space.
+	 */
+	if (ghes_is_synchronous(ghes) && current->mm != &init_mm) {
+		callback = kzalloc(sizeof(*callback), GFP_ATOMIC);
+		if (!callback)
+			return;
+		callback->work.func = ghes_kick_memory_failure;
+		callback->cpu = smp_processor_id();
+		ret = task_work_add(current, &callback->work, true);
+		if (ret)
+			kfree(callback);
+	}
 }
 
 /*
@@ -480,7 +535,7 @@ static void ghes_do_proc(struct ghes *ghes,
 			ghes_edac_report_mem_error(sev, mem_err);
 
 			arch_apei_report_mem_error(sev, mem_err);
-			ghes_handle_memory_failure(gdata, sev);
+			ghes_handle_memory_failure(ghes, gdata, sev);
 		}
 		else if (guid_equal(sec_type, &CPER_SEC_PCIE)) {
 			ghes_handle_aer(gdata);
-- 
2.19.2


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