Re: [PATCH v6 07/18] arm64: KVM/mm: Move SEA handling behind a single 'claim' interface

Borislav Petkov
2018-10-12T10:02:15Z

On Fri, Sep 21, 2018 at 11:16:54PM +0100, James Morse wrote:
> To split up APEIs in_nmi() path, we need the nmi-like callers to always
> be in_nmi(). Add a helper to do the work and claim the notification.
>
> When KVM or the arch code takes an exception that might be a RAS
> notification, it asks the APEI firmware-first code whether it wants
> to claim the exception. We can then go on to see if (a future)
> kernel-first mechanism wants to claim the notification, before
> falling through to the existing default behaviour.
>
> The NOTIFY_SEA code was merged before we had multiple, possibly
> interacting, NMI-like notifications and the need to consider kernel
> first in the future. Make the 'claiming' behaviour explicit.
>
> As we're restructuring the APEI code to allow multiple NMI-like
> notifications, any notification that might interrupt interrupts-masked
> code must always be wrapped in nmi_enter()/nmi_exit(). This allows APEI
> to use in_nmi() to use the right fixmap entries.
>
> We mask SError over this window to prevent an asynchronous RAS error
> arriving and tripping 'nmi_enter()'s BUG_ON(in_nmi()).
>
> Signed-off-by: James Morse <james.morse@arm.com>
> Acked-by: Marc Zyngier <marc.zyngier@arm.com>
> Tested-by: Tyler Baicar <tbaicar@codeaurora.org>

...

> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> index ed46dc188b22..a9b8bba014b5 100644
> --- a/arch/arm64/kernel/acpi.c
> +++ b/arch/arm64/kernel/acpi.c
> @@ -28,8 +28,10 @@
> #include <linux/smp.h>
> #include <linux/serial_core.h>
>
> +#include <acpi/ghes.h>
> #include <asm/cputype.h>
> #include <asm/cpu_ops.h>
> +#include <asm/daifflags.h>
> #include <asm/pgtable.h>
> #include <asm/smp_plat.h>
>
> @@ -257,3 +259,30 @@ pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
> return __pgprot(PROT_NORMAL_NC);
> return __pgprot(PROT_DEVICE_nGnRnE);
> }
> +
> +/*
> + * Claim Synchronous External Aborts as a firmware first notification.
> + *
> + * Used by KVM and the arch do_sea handler.
> + * @regs may be NULL when called from process context.
> + */
> +int apei_claim_sea(struct pt_regs *regs)
> +{
> + int err = -ENOENT;
> + unsigned long current_flags = arch_local_save_flags();
> +
> + if (!IS_ENABLED(CONFIG_ACPI_APEI_SEA))
> + return err;

I don't know what side effects arch_local_save_flags() has on ARM but if
we return here, it looks to me like useless work.

--
Regards/Gruss,
Boris.

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