* Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> KVM PV EOI optimization overrides eoi_write apic op with its own
> version. Add an API for this to avoid meddling with core x86 apic driver
> data structures directly.
>
> For KVM use, we don't need any guarantees about when the switch to the
> new op will take place, so it could in theory use this API after SMP init,
> but it currently doesn't, and restricting callers to early init makes it
> clear that it's safe as it won't race with actual APIC driver use.
>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> arch/x86/include/asm/apic.h | 3 +++
> arch/x86/kernel/apic/apic.c | 17 +++++++++++++++++
> 2 files changed, 20 insertions(+)
>
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index aa5b2ee..ff8dff6 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -469,6 +469,8 @@ static inline u32 safe_apic_wait_icr_idle(void)
> return apic->safe_wait_icr_idle();
> }
>
> +extern void __init apic_set_eoi_write(void (*eoi_write)(u32 reg, u32 v));
> +
> #else /* CONFIG_X86_LOCAL_APIC */
>
> static inline u32 apic_read(u32 reg) { return 0; }
> @@ -478,6 +480,7 @@ static inline u64 apic_icr_read(void) { return 0; }
> static inline void apic_icr_write(u32 low, u32 high) { }
> static inline void apic_wait_icr_idle(void) { }
> static inline u32 safe_apic_wait_icr_idle(void) { return 0; }
> +static inline void apic_set_eoi_write(void (*eoi_write)(u32 reg, u32 v)) {}
>
> #endif /* CONFIG_X86_LOCAL_APIC */
>
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 39a222e..c7520b6 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -2124,6 +2124,23 @@ void default_init_apic_ldr(void)
> }
>
> /*
> + * Override the generic EOI implementation with an optimized version.
> + * Only called during early boot when only one CPU is active and with
> + * interrupts disabled, so we know this does not race with actual APIC driver
> + * use.
> + */
> +void __init apic_set_eoi_write(void (*eoi_write)(u32 reg, u32 v))
> +{
> + struct apic **drv;
> +
> + for (drv = __apicdrivers; drv < __apicdrivers_end; drv++) {
> + /* Should happen once for each apic */
> + WARN_ON((*drv)->eoi_write == eoi_write);
> + (*drv)->eoi_write = eoi_write;
> + }
> +}
> +
ok, it's better this way.
Acked-by: Ingo Molnar <mingo@xxxxxxxxxx>
Thanks,
Ingo
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