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Message-ID: <20230721201859.2307736-20-seanjc@google.com>
Date: Fri, 21 Jul 2023 13:18:59 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
Andrew Cooper <Andrew.Cooper3@...rix.com>,
Kai Huang <kai.huang@...el.com>, Chao Gao <chao.gao@...el.com>
Subject: [PATCH v4 19/19] KVM: VMX: Skip VMCLEAR logic during emergency
reboots if CR4.VMXE=0
Bail from vmx_emergency_disable() without processing the list of loaded
VMCSes if CR4.VMXE=0, i.e. if the CPU can't be post-VMXON. It should be
impossible for the list to have entries if VMX is already disabled, and
even if that invariant doesn't hold, VMCLEAR will #UD anyways, i.e.
processing the list is pointless even if it somehow isn't empty.
Assuming no existing KVM bugs, this should be a glorified nop. The
primary motivation for the change is to avoid having code that looks like
it does VMCLEAR, but then skips VMXON, which is nonsensical.
Suggested-by: Kai Huang <kai.huang@...el.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
arch/x86/kvm/vmx/vmx.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 5d21931842a5..0ef5ede9cb7c 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -773,12 +773,20 @@ static void vmx_emergency_disable(void)
kvm_rebooting = true;
+ /*
+ * Note, CR4.VMXE can be _cleared_ in NMI context, but it can only be
+ * set in task context. If this races with VMX is disabled by an NMI,
+ * VMCLEAR and VMXOFF may #UD, but KVM will eat those faults due to
+ * kvm_rebooting set.
+ */
+ if (!(__read_cr4() & X86_CR4_VMXE))
+ return;
+
list_for_each_entry(v, &per_cpu(loaded_vmcss_on_cpu, cpu),
loaded_vmcss_on_cpu_link)
vmcs_clear(v->vmcs);
- if (__read_cr4() & X86_CR4_VMXE)
- kvm_cpu_vmxoff();
+ kvm_cpu_vmxoff();
}
static void __loaded_vmcs_clear(void *arg)
--
2.41.0.487.g6d72f3e995-goog
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