From: Auger Eric <eric.auger@redhat.com>
To: Alexandru Elisei <alexandru.elisei@arm.com>,
kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu,
drjones@redhat.com
Cc: andre.przywara@arm.com
Subject: Re: [kvm-unit-tests PATCH 07/10] arm/arm64: gic: Wait for writes to acked or spurious to complete
Date: Thu, 3 Dec 2020 14:21:29 +0100 [thread overview]
Message-ID: <179b4f5f-8bdf-1922-f79a-930bde2ed103@redhat.com> (raw)
In-Reply-To: <20201125155113.192079-8-alexandru.elisei@arm.com>
Hi Alexandru,
On 11/25/20 4:51 PM, Alexandru Elisei wrote:
> The IPI test has two parts: in the first part, it tests that the sender CPU
> can send an IPI to itself (ipi_test_self()), and in the second part it
> sends interrupts to even-numbered CPUs (ipi_test_smp()). When acknowledging
> an interrupt, if we read back a spurious interrupt ID (1023), the handler
> increments the index in the static array spurious corresponding to the CPU
> ID that the handler is running on; if we get the expected interrupt ID, we
> increment the same index in the acked array.
>
> Reads of the spurious and acked arrays are synchronized with writes
> performed before sending the IPI. The synchronization is done either in the
> IPI sender function (GICv3), either by creating a data dependency (GICv2).
>
> At the end of the test, the sender CPU reads from the acked and spurious
> arrays to check against the expected behaviour. We need to make sure the
> that writes in ipi_handler() are observable by the sender CPU. Use a DSB
> ISHST to make sure that the writes have completed.
>
> One might rightfully argue that there are no guarantees regarding when the
> DSB instruction completes, just like there are no guarantees regarding when
> the value is observed by the other CPUs. However, let's do our best and
> instruct the CPU to complete the memory access when we know that it will be
> needed.
>
> We still need to follow the message passing pattern for the acked,
> respectively bad_irq and bad_sender, because DSB guarantees that all memory
> accesses that come before the barrier have completed, not that they have
> completed in program order.
I guess the removal of the smp_rmb in check_spurious should belong to
that patch?
>
> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Besides, AFAIU
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Thanks
Eric
> ---
> arm/gic.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arm/gic.c b/arm/gic.c
> index 5727d72a0ef3..544c283f5f47 100644
> --- a/arm/gic.c
> +++ b/arm/gic.c
> @@ -161,8 +161,10 @@ static void ipi_handler(struct pt_regs *regs __unused)
> ++acked[smp_processor_id()];
> } else {
> ++spurious[smp_processor_id()];
> - smp_wmb();
> }
> +
> + /* Wait for writes to acked/spurious to complete */
> + dsb(ishst);
> }
>
> static void setup_irq(irq_handler_fn handler)
>
next prev parent reply other threads:[~2020-12-03 13:23 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-25 15:51 [kvm-unit-tests PATCH 00/10] GIC fixes and improvements Alexandru Elisei
2020-11-25 15:51 ` [kvm-unit-tests PATCH 01/10] lib: arm/arm64: gicv3: Add missing barrier when sending IPIs Alexandru Elisei
2020-12-01 16:37 ` Auger Eric
2020-12-01 17:37 ` Alexandru Elisei
2020-11-25 15:51 ` [kvm-unit-tests PATCH 02/10] lib: arm/arm64: gicv2: " Alexandru Elisei
2020-12-01 16:37 ` Auger Eric
2020-11-25 15:51 ` [kvm-unit-tests PATCH 03/10] arm/arm64: gic: Remove memory synchronization from ipi_clear_active_handler() Alexandru Elisei
2020-12-01 16:37 ` Auger Eric
2020-12-02 14:02 ` Alexandru Elisei
2020-12-02 14:14 ` Alexandru Elisei
2020-12-03 9:41 ` Auger Eric
2020-11-25 15:51 ` [kvm-unit-tests PATCH 04/10] arm/arm64: gic: Remove unnecessary synchronization with stats_reset() Alexandru Elisei
2020-12-01 16:48 ` Auger Eric
2020-12-02 14:06 ` Alexandru Elisei
2020-12-03 13:10 ` Auger Eric
2020-11-25 15:51 ` [kvm-unit-tests PATCH 05/10] arm/arm64: gic: Use correct memory ordering for the IPI test Alexandru Elisei
2020-12-03 13:10 ` Auger Eric
2020-12-03 13:21 ` Alexandru Elisei
2020-11-25 15:51 ` [kvm-unit-tests PATCH 06/10] arm/arm64: gic: Check spurious and bad_sender in the active test Alexandru Elisei
2020-12-03 13:10 ` Auger Eric
2020-11-25 15:51 ` [kvm-unit-tests PATCH 07/10] arm/arm64: gic: Wait for writes to acked or spurious to complete Alexandru Elisei
2020-12-03 13:21 ` Auger Eric [this message]
2020-11-25 15:51 ` [kvm-unit-tests PATCH 08/10] arm/arm64: gic: Split check_acked() into two functions Alexandru Elisei
2020-12-03 13:39 ` Auger Eric
2020-12-10 14:45 ` Alexandru Elisei
2020-12-15 13:58 ` Auger Eric
2020-12-16 11:40 ` Alexandru Elisei
2020-12-16 12:37 ` Auger Eric
2020-11-25 15:51 ` [kvm-unit-tests PATCH 09/10] arm/arm64: gic: Make check_acked() more generic Alexandru Elisei
2020-12-03 14:59 ` Auger Eric
2020-11-25 15:51 ` [kvm-unit-tests PATCH 10/10] arm64: gic: Use IPI test checking for the LPI tests Alexandru Elisei
2020-11-26 9:30 ` Zenghui Yu
2020-11-27 14:50 ` Alexandru Elisei
2020-11-30 13:59 ` Zenghui Yu
2020-11-30 14:19 ` Alexandru Elisei
2020-12-01 15:09 ` Alexandru Elisei
2020-11-30 17:48 ` Auger Eric
2020-12-03 14:59 ` Auger Eric
2020-12-09 10:29 ` Alexandru Elisei
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