Re: [kvm-unit-tests PATCH v3 04/11] arm/arm64: gic: Remove unnecessary synchronization with stats_reset()

[Auger Eric]

Hi,

On 1/29/21 5:36 PM, Alexandru Elisei wrote:
> The GICv3 driver executes a DSB barrier before sending an IPI, which
> ensures that memory accesses have completed. This removes the need to
> enforce ordering with respect to stats_reset() in the IPI handler.
> 
> For GICv2, the same barrier is executed by readl() after the MMIO read.
> Together with the wmb() barrier from writel() when triggering the IPI,
> this ensures that the expected memory ordering is respected.
> 
> Signed-off-by: Alexandru Elisei 
Reviewed-by: Eric Auger 

Eric

> ---
>  arm/gic.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/arm/gic.c b/arm/gic.c
> index 8bb804abf34d..db1417ae1ca1 100644
> --- a/arm/gic.c
> +++ b/arm/gic.c
> @@ -59,7 +59,6 @@ static void stats_reset(void)
>   bad_sender[i] = -1;
>   bad_irq[i] = -1;
>   }
> - smp_wmb();
>  }
>  
>  static void check_acked(const char *testname, cpumask_t *mask)
> @@ -149,7 +148,6 @@ static void ipi_handler(struct pt_regs *regs __unused)
>  
>   if (irqnr != GICC_INT_SPURIOUS) {
>   gic_write_eoir(irqstat);
> - smp_rmb(); /* pairs with wmb in stats_reset */
>   ++acked[smp_processor_id()];
>   check_ipi_sender(irqstat);
>   check_irqnr(irqnr);
> 

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[kvm-unit-tests PATCH v3 04/11] arm/arm64: gic: Remove unnecessary synchronization with stats_reset()

[Alexandru Elisei]

The GICv3 driver executes a DSB barrier before sending an IPI, which
ensures that memory accesses have completed. This removes the need to
enforce ordering with respect to stats_reset() in the IPI handler.

For GICv2, the same barrier is executed by readl() after the MMIO read.
Together with the wmb() barrier from writel() when triggering the IPI,
this ensures that the expected memory ordering is respected.

Signed-off-by: Alexandru Elisei 
---
 arm/gic.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arm/gic.c b/arm/gic.c
index 8bb804abf34d..db1417ae1ca1 100644
--- a/arm/gic.c
+++ b/arm/gic.c
@@ -59,7 +59,6 @@ static void stats_reset(void)
bad_sender[i] = -1;
bad_irq[i] = -1;
}
-   smp_wmb();
 }
 
 static void check_acked(const char *testname, cpumask_t *mask)
@@ -149,7 +148,6 @@ static void ipi_handler(struct pt_regs *regs __unused)
 
if (irqnr != GICC_INT_SPURIOUS) {
gic_write_eoir(irqstat);
-   smp_rmb(); /* pairs with wmb in stats_reset */
++acked[smp_processor_id()];
check_ipi_sender(irqstat);
check_irqnr(irqnr);
-- 
2.30.0

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