Re: [PATCH v1 0/2] KVM: arm: Refuse to enable KVM on systems with SME but not FGT
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2022-10-30 17:46:00
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kvmarm
On Sat, Oct 29, 2022 at 12:46:43PM +0100, Marc Zyngier wrote:
On Thu, 27 Oct 2022 21:52:44 +0100, Mark Brown [off-list ref] wrote:quoted
The architecture requires that any system which implements SME also has fine grained traps since SME is a v9.2 feature, meaning that v8.7 must be implemented, and FGT is mandatory from v8.6. SME relies on fine grained traps to control access to SMPRI_EL1 and in nVHE mode to TPIDR2_EL0, without traps SMPRI_EL1.Priority and TPIDR2_EL0 can be used as side channels. This series adds support for detecting FGT and refuses to allow KVM to be used in architecturally invalid configurations which have SME but not FGT, without detection the issue presents as faults due to EL2 attempting to access the FGT registers which isn't obvious to users. Currently fine grained traps are only used in nVHE but but a series "arm64/sme: Fix SMPRI_EL1 traps for KVM guests" sent along with this will add usage for VHE mode too making the issue more pressing.I think this goes the wrong way around. SME without FGT is invalid, and yet you keep SME around and device to kill virtualisation support. I'd rather it is SME that gets disabled when the kernel boots at EL2.
I agree, I rather we did it the other way around. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel