Re: [PATCH v8 24/26] arm64: acpi: Make apei_claim_sea() synchronise with APEI's irq work

[Julien Thierry <julien.thierry@arm.com>]

Hi James,

On 29/01/2019 18:49, James Morse wrote:
> 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>
> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
> CC: Xie XiuQi <xiexiuqi@huawei.com>
> CC: gengdongjiu <gengdongjiu@huawei.com>
> 
> ---
> Changes since v7:
>  * Added Catalin's ack, then:
>  * Added __irq_enter()/exit() calls so if we interrupted preemptible code, the
>    preempt count matches what other irq-work expects.
>  * Changed the 'if (!arch_irqs_disabled_flags(interrupted_flags))' test to be
>    safe before/after Julien's PMR series.
> 
> 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 | 23 +++++++++++++++++++++++
>  arch/arm64/mm/fault.c    |  9 ++++-----
>  2 files changed, 27 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> index 803f0494dd3e..8288ae0c8f3b 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>
> @@ -268,12 +269,17 @@ pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
>  int apei_claim_sea(struct pt_regs *regs)
>  {
>  	int err = -ENOENT;
> +	bool return_to_irqs_enabled;
>  	unsigned long current_flags;
>  
>  	if (!IS_ENABLED(CONFIG_ACPI_APEI_GHES))
>  		return err;
>  
>  	current_flags = arch_local_save_flags();
> +	return_to_irqs_enabled = !irqs_disabled_flags(current_flags);
> +
> +	if (regs)
> +		return_to_irqs_enabled = interrupts_enabled(regs);
>  
>  	/*
>  	 * SEA can interrupt SError, mask it and describe this as an NMI so
> @@ -283,6 +289,23 @@ 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 (return_to_irqs_enabled) {
> +			local_daif_restore(DAIF_PROCCTX_NOIRQ);
> +			__irq_enter();
> +			irq_work_run();
> +			__irq_exit();
> +		} else {
> +			pr_warn("APEI work queued but not completed");
> +			err = -EINPROGRESS;
> +		}
> +	}
> +

Reviewed-by: Julien Thierry <julien.thierry@arm.com>

Cheers,

-- 
Julien Thierry

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel