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Message-ID: <20231018193617.1895752-1-seanjc@google.com>
Date: Wed, 18 Oct 2023 12:36:17 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
Tom Lendacky <thomas.lendacky@....com>
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 <thomas.lendacky@....com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
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 4900c078045a..d0c580607f00 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 */
base-commit: 437bba5ad2bba00c2056c896753a32edf80860cc
--
2.42.0.655.g421f12c284-goog
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