[PATCH v7 23/25] arm64: acpi: Make apei_claim_sea() synchronise with APEI's irq work

James Morse
2018-12-03T18:08:01Z

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>
Reviewed-by: Punit Agrawal <punit.agrawal@arm.com>
Tested-by: Tyler Baicar <tbaicar@codeaurora.org>
CC: Xie XiuQi <xiexiuqi@huawei.com>
CC: gengdongjiu <gengdongjiu@huawei.com>
---
Changes since v6:
* Added pr_warn() for the EINPROGRESS case so panic-tracebacks show
'APEI was here'.
* Tinkered with the commit message

Changes since v2:
* Removed IS_ENABLED() check, done by the caller unless we have a dummy
definition.
---
arch/arm64/kernel/acpi.c | 22 +++++++++++++++++++++-
arch/arm64/mm/fault.c | 9 ++++-----
2 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index 803f0494dd3e..421331157e8f 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c
@@ -22,6 +22,7 @@
#include <linux/init.h>
#include <linux/irq.h>
#include <linux/irqdomain.h>
+#include <linux/irq_work.h>
#include <linux/memblock.h>
#include <linux/of_fdt.h>
#include <linux/smp.h>
@@ -268,13 +269,17 @@ pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
int apei_claim_sea(struct pt_regs *regs)
{
int err = -ENOENT;
- unsigned long current_flags;
+ unsigned long current_flags, interrupted_flags;

if (!IS_ENABLED(CONFIG_ACPI_APEI_GHES))
return err;

current_flags = arch_local_save_flags();

+ interrupted_flags = current_flags;
+ if (regs)
+ interrupted_flags = regs->pstate;
+
/*
* SEA can interrupt SError, mask it and describe this as an NMI so
* that APEI defers the handling.
@@ -283,6 +288,21 @@ int apei_claim_sea(struct pt_regs *regs)
nmi_enter();
err = ghes_notify_sea();
nmi_exit();
+
+ /*
+ * APEI NMI-like notifications are deferred to irq_work. Unless
+ * we interrupted irqs-masked code, we can do that now.
+ */
+ if (!err) {
+ if (!arch_irqs_disabled_flags(interrupted_flags)) {
+ local_daif_restore(DAIF_PROCCTX_NOIRQ);
+ irq_work_run();
+ } else {
+ pr_warn("APEI work queued but not completed");
+ err = -EINPROGRESS;
+ }
+ }
+
local_daif_restore(current_flags);

return err;
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 956afc7d932a..c26ee1f1cc36 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -629,11 +629,10 @@ 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 (apei_claim_sea(regs) == 0) {
+ /* APEI claimed this as a firmware-first notification */
+ return 0;
+ }

if (esr & ESR_ELx_FnV)
siaddr = NULL;
--
2.19.2