linux-kernel - Re: [PATCH] KVM: arm64: Don't hypercall before EL2 init

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Message-ID: <YoIqdiOoCf0A1hcV@google.com>
Date:   Mon, 16 May 2022 10:41:58 +0000
From:   Quentin Perret <qperret@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH] KVM: arm64: Don't hypercall before EL2 init

On Sunday 15 May 2022 at 12:10:20 (+0100), Marc Zyngier wrote:
> Can we simplify the condition? ARM64_SPECTRE_V3A is only set when
> !VHE, and we already bail in kvm_patch_vector_branch() if we see
> VHE+V3A, because the combination makes no sense at all. I think this
> can be rewritten as:
> 
> 	if (kvm_system_needs_idmapped_vectors() &&
> 	    !is_protected_lvm_enabled())
> 
> Thoughts?

Yup I think this works as both CPUs that are vulnerable to V3A aren't
VHE-capable. But if we ever get a VHE-capable CPU that's vulnerable I
think the next call to create_hyp_exec_mappings() will BUG(). Perhaps
the alternative would be to have has_spectre_v3a() say no in VHE to be
on the safe side? That is, prevent the cap from being set to begin with.

Cheers,
Quentin