From: Mark Rutland <mark.rutland@arm.com>
To: Marc Zyngier <maz@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
kvmarm@lists.cs.columbia.edu, James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
Eric Auger <eric.auger@redhat.com>,
Hector Martin <marcan@marcan.st>,
kernel-team@android.com
Subject: Re: [PATCH v3 3/9] KVM: arm64: vgic: Be tolerant to the lack of maintenance interrupt
Date: Mon, 10 May 2021 17:19:07 +0100 [thread overview]
Message-ID: <20210510161907.GD92897@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20210510134824.1910399-4-maz@kernel.org>
On Mon, May 10, 2021 at 02:48:18PM +0100, Marc Zyngier wrote:
> As it turns out, not all the interrupt controllers are able to
> expose a vGIC maintenance interrupt as a distrete signal.
> And to be fair, it doesn't really matter as all we require is
> for *something* to kick us out of guest mode out way or another.
>
> On systems that do not expose a maintenance interrupt as such,
> there are two outcomes:
>
> - either the virtual CPUIF does generate an interrupt, and
> by the time we are back to the host the interrupt will have long
> been disabled (as we set ICH_HCR_EL2.EN to 0 on exit). In this case,
> interrupt latency is as good as it gets.
>
> - or some other event (physical timer) will take us out of the guest
> anyway, and the only drawback is a bad interrupt latency.
IIRC we won't have a a guaranteed schedular tick for NO_HZ_FULL, so in
that case we'll either need to set a period software maintenance
interrupt, or reject this combination at runtime (either when trying to
isolate the dynticks CPUs, or when trying to create a VM).
Otherwise, it's very likely that something will take us out of the guest
from time to time, but we won't have a strict guarantee (e.g. if all
guest memory is pinned).
Thanks,
Mark.
>
> So let's be tolerant to the lack of maintenance interrupt, and just let
> the user know that their mileage may vary...
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/kvm/vgic/vgic-init.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
> index 2fdb65529594..9fd23f32aa54 100644
> --- a/arch/arm64/kvm/vgic/vgic-init.c
> +++ b/arch/arm64/kvm/vgic/vgic-init.c
> @@ -524,11 +524,6 @@ int kvm_vgic_hyp_init(void)
> if (!gic_kvm_info)
> return -ENODEV;
>
> - if (!gic_kvm_info->maint_irq) {
> - kvm_err("No vgic maintenance irq\n");
> - return -ENXIO;
> - }
> -
> switch (gic_kvm_info->type) {
> case GIC_V2:
> ret = vgic_v2_probe(gic_kvm_info);
> @@ -552,6 +547,11 @@ int kvm_vgic_hyp_init(void)
> if (ret)
> return ret;
>
> + if (!kvm_vgic_global_state.maint_irq) {
> + kvm_err("No maintenance interrupt available, fingers crossed...\n");
> + return 0;
> + }
> +
> ret = request_percpu_irq(kvm_vgic_global_state.maint_irq,
> vgic_maintenance_handler,
> "vgic", kvm_get_running_vcpus());
> --
> 2.29.2
>
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next prev parent reply other threads:[~2021-05-10 16:21 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-10 13:48 [PATCH v3 0/9] KVM: arm64: Initial host support for the Apple M1 Marc Zyngier
2021-05-10 13:48 ` [PATCH v3 1/9] irqchip/gic: Split vGIC probing information from the GIC code Marc Zyngier
2021-05-18 16:51 ` Alexandru Elisei
2021-05-10 13:48 ` [PATCH v3 2/9] KVM: arm64: Handle physical FIQ as an IRQ while running a guest Marc Zyngier
2021-05-20 17:46 ` Alexandru Elisei
2021-05-10 13:48 ` [PATCH v3 3/9] KVM: arm64: vgic: Be tolerant to the lack of maintenance interrupt Marc Zyngier
2021-05-10 16:19 ` Mark Rutland [this message]
2021-05-10 17:44 ` Marc Zyngier
2021-05-11 11:13 ` Mark Rutland
2021-05-10 13:48 ` [PATCH v3 4/9] KVM: arm64: vgic: Let an interrupt controller advertise lack of HW deactivation Marc Zyngier
2021-05-21 17:01 ` Alexandru Elisei
2021-05-24 17:17 ` Marc Zyngier
2021-05-10 13:48 ` [PATCH v3 5/9] KVM: arm64: vgic: move irq->get_input_level into an ops structure Marc Zyngier
2021-05-10 13:48 ` [PATCH v3 6/9] KVM: arm64: vgic: Implement SW-driven deactivation Marc Zyngier
2021-05-24 16:53 ` Alexandru Elisei
2021-05-24 17:43 ` Marc Zyngier
2021-05-10 13:48 ` [PATCH v3 7/9] KVM: arm64: timer: Refactor IRQ configuration Marc Zyngier
2021-05-14 12:46 ` Zenghui Yu
2021-05-24 17:48 ` Marc Zyngier
2021-05-10 13:48 ` [PATCH v3 8/9] KVM: arm64: timer: Add support for SW-based deactivation Marc Zyngier
2021-05-10 13:48 ` [PATCH v3 9/9] irqchip/apple-aic: Advertise some level of vGICv3 compatibility Marc Zyngier
2021-05-12 16:22 ` [PATCH v3 0/9] KVM: arm64: Initial host support for the Apple M1 Alexandru Elisei
2021-05-12 16:33 ` Marc Zyngier
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