KVM: x86: Return "unsupported" instead of "invalid" on access to unsupported PV MSR

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[ Upstream commit 5bb9ac1865 ]

Return KVM_MSR_RET_UNSUPPORTED instead of '1' (which for all intents and
purposes means "invalid") when rejecting accesses to KVM PV MSRs to adhere
to KVM's ABI of allowing host reads and writes of '0' to MSRs that are
advertised to userspace via KVM_GET_MSR_INDEX_LIST, even if the vCPU model
doesn't support the MSR.

E.g. running a QEMU VM with

  -cpu host,-kvmclock,kvm-pv-enforce-cpuid

yields:

  qemu: error: failed to set MSR 0x12 to 0x0
  qemu: target/i386/kvm/kvm.c:3301: kvm_buf_set_msrs:
        Assertion `ret == cpu->kvm_msr_buf->nmsrs' failed.

Fixes: 66570e966d ("kvm: x86: only provide PV features if enabled in guest's CPUID")
Cc: stable@vger.kernel.org
Reviewed-by: Jim Mattson <jmattson@google.com>
Link: https://patch.msgid.link/20251230205948.4094097-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

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Sean Christopherson 2025-12-30 12:59:48 -08:00 • committed by Sasha Levin

parent b61843503d

commit c481d4edf0

1 changed files with 20 additions and 20 deletions

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arch/x86/kvm/x86.c

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