From: Will Deacon <will@kernel.org>
To: Marc Zyngier <maz@kernel.org>
Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
kvm@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Oliver Upton <oliver.upton@linux.dev>,
Zenghui Yu <yuzenghui@huawei.com>
Subject: Re: [PATCH 1/2] KVM: arm64: Disable KVM on systems with a VPIPT i-cache
Date: Fri, 20 Jan 2023 10:14:16 +0000 [thread overview]
Message-ID: <20230120101415.GA21784@willie-the-truck> (raw)
In-Reply-To: <20230113172523.2063867-2-maz@kernel.org>
On Fri, Jan 13, 2023 at 05:25:22PM +0000, Marc Zyngier wrote:
> Systems with a VMID-tagged PIPT i-cache have been supported for
> a while by Linux and KVM. However, these systems never appeared
> on our side of the multiverse.
>
> Refuse to initialise KVM on such a machine, should then ever appear.
> Following changes will drop the support from the hypervisor.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/kvm/arm.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 9c5573bc4614..508deed213a2 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -2195,6 +2195,11 @@ int kvm_arch_init(void *opaque)
> int err;
> bool in_hyp_mode;
>
> + if (icache_is_vpipt()) {
> + kvm_info("Incompatible VPIPT I-Cache policy\n");
> + return -ENODEV;
> + }
Hmm, does this work properly with late CPU onlining? For example, if my set
of boot CPUs are all friendly PIPT and KVM initialises happily, but then I
late online a CPU with a horrible VPIPT policy, I worry that we'll quietly
do the wrong thing wrt maintenance.
If that's the case, then arguably we already have a bug in the cases where
we trap and emulate accesses to CTR_EL0 from userspace because I _think_
we'll change the L1Ip field at runtime after userspace could've already read
it.
Is there something that stops us from ended up in this situation?
Will
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next prev parent reply other threads:[~2023-01-20 10:17 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-13 17:25 [PATCH 0/2] KVM: arm64: Drop support for VPIPT i-cache policy Marc Zyngier
2023-01-13 17:25 ` [PATCH 1/2] KVM: arm64: Disable KVM on systems with a VPIPT i-cache Marc Zyngier
2023-01-20 10:14 ` Will Deacon [this message]
2023-01-20 11:49 ` Marc Zyngier
2023-01-13 17:25 ` [PATCH 2/2] KVM: arm64: Remove VPIPT I-cache handling Marc Zyngier
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