From: Marc Zyngier <maz@kernel.org>
To: "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc: Barry Song <21cnbao@gmail.com>,
tglx@linutronix.de, will@kernel.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linuxarm@huawei.com,
Barry Song <song.bao.hua@hisilicon.com>
Subject: Re: [PATCH] irqchip/gic-v3: use dsb(ishst) to synchronize data to smp before issuing ipi
Date: Sun, 20 Feb 2022 15:21:15 +0000 [thread overview]
Message-ID: <c10d6044786fdf78ef4bc7fac2544096@kernel.org> (raw)
In-Reply-To: <YhJYct7aW0kGXNXp@shell.armlinux.org.uk>
On 2022-02-20 15:04, Russell King (Oracle) wrote:
> On Sat, Feb 19, 2022 at 05:55:49AM +0800, Barry Song wrote:
>> dsb(ishst) should be enough here as we only need to guarantee the
>> visibility of data to other CPUs in smp inner domain before we
>> send the ipi.
>>
>> Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
>> ---
>> drivers/irqchip/irq-gic-v3.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3.c
>> b/drivers/irqchip/irq-gic-v3.c
>> index 5e935d97207d..0efe1a9a9f3b 100644
>> --- a/drivers/irqchip/irq-gic-v3.c
>> +++ b/drivers/irqchip/irq-gic-v3.c
>> @@ -1211,7 +1211,7 @@ static void gic_ipi_send_mask(struct irq_data
>> *d, const struct cpumask *mask)
>> * Ensure that stores to Normal memory are visible to the
>> * other CPUs before issuing the IPI.
>> */
>> - wmb();
>> + dsb(ishst);
>
> On ARM, wmb() is a dsb(st) followed by other operations which may
> include a sync operation at the L2 cache, and SoC specific barriers
> for the bus. Hopefully, nothing will break if the sledge hammer is
> replaced by the tack hammer.
The saving grace is that ARMv8 forbids (as per D4.4.11) these
SW-visible,
non architected caches (something like PL310 simply isn't allowed).
Given
that GICv3 requires ARMv8 the first place, we should be OK.
As for SoC-specific bus barriers, I don't know of any that would affect
an ARMv8 based SoC. But I'm always prepared to be badly surprised...
M.
--
Jazz is not dead. It just smells funny...
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next prev parent reply other threads:[~2022-02-20 15:22 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-18 21:55 [PATCH] irqchip/gic-v3: use dsb(ishst) to synchronize data to smp before issuing ipi Barry Song
2022-02-19 9:56 ` Marc Zyngier
2022-02-19 23:46 ` Barry Song
2022-02-20 1:33 ` Barry Song
2022-02-20 13:30 ` Ard Biesheuvel
2022-02-20 15:04 ` Marc Zyngier
2022-02-20 15:05 ` Russell King (Oracle)
2022-02-20 20:09 ` Barry Song
2022-02-20 15:04 ` Russell King (Oracle)
2022-02-20 15:21 ` Marc Zyngier [this message]
2022-02-20 20:20 ` Barry Song
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