From 770d6aa2e416fd26f0356e258c77a37574ad9b8c Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 18 Oct 2023 12:36:17 -0700 Subject: [PATCH] KVM: SVM: Explicitly require FLUSHBYASID to enable SEV support Add a sanity check that FLUSHBYASID is available if SEV is supported in hardware, as SEV (and beyond) guests are bound to a single ASID, i.e. KVM can't "flush" by assigning a new, fresh ASID to the guest. If FLUSHBYASID isn't supported for some bizarre reason, KVM would completely fail to do TLB flushes for SEV+ guests (see pre_svm_run() and pre_sev_run()). Cc: Tom Lendacky Link: https://lore.kernel.org/r/20231018193617.1895752-1-seanjc@google.com Signed-off-by: Sean Christopherson --- arch/x86/kvm/svm/sev.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 4900c078045ac..d0c580607f009 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -2191,10 +2191,13 @@ void __init sev_hardware_setup(void) /* * SEV must obviously be supported in hardware. Sanity check that the * CPU supports decode assists, which is mandatory for SEV guests to - * support instruction emulation. + * support instruction emulation. Ditto for flushing by ASID, as SEV + * guests are bound to a single ASID, i.e. KVM can't rotate to a new + * ASID to effect a TLB flush. */ if (!boot_cpu_has(X86_FEATURE_SEV) || - WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_DECODEASSISTS))) + WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_DECODEASSISTS)) || + WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_FLUSHBYASID))) goto out; /* Retrieve SEV CPUID information */ -- 2.30.2