arm64: acpi: Make apei_claim_sea() synchronise with APEI's irq work

APEI is unable to do all of its error handling work in nmi-context, so
it defers non-fatal work onto the irq_work queue. arch_irq_work_raise()
sends an IPI to the calling cpu, but this is not guaranteed to be taken
before returning to user-space.

Unless the exception interrupted a context with irqs-masked,
irq_work_run() can run immediately. Otherwise return -EINPROGRESS to
indicate ghes_notify_sea() found some work to do, but it hasn't
finished yet.

With this apei_claim_sea() returning '0' means this external-abort was
also notification of a firmware-first RAS error, and that APEI has
processed the CPER records.

Signed-off-by: James Morse <james.morse@arm.com>
Tested-by: Tyler Baicar <baicar@os.amperecomputing.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index c9cedc0432d2..dff2d72b0883 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -635,11 +635,13 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
 
 	inf = esr_to_fault_info(esr);
 
-	/*
-	 * Return value ignored as we rely on signal merging.
-	 * Future patches will make this more robust.
-	 */
-	apei_claim_sea(regs);
+	if (user_mode(regs) && apei_claim_sea(regs) == 0) {
+		/*
+		 * APEI claimed this as a firmware-first notification.
+		 * Some processing deferred to task_work before ret_to_user().
+		 */
+		return 0;
+	}
 
 	if (esr & ESR_ELx_FnV)
 		siaddr = NULL;