linux-kernel - [PATCH 2/3] KVM: VMX: return early if msr

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Date: Fri, 16 Feb 2024 17:45:12 -0800
From: Dongli Zhang <dongli.zhang@...cle.com>
To: kvm@...r.kernel.org
Cc: seanjc@...gle.com, pbonzini@...hat.com, linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] KVM: VMX: return early if msr_bitmap is not supported

The vmx_msr_filter_changed() may directly/indirectly calls only
vmx_enable_intercept_for_msr() or vmx_disable_intercept_for_msr(). Those
two functions may exit immediately if !cpu_has_vmx_msr_bitmap().

vmx_msr_filter_changed()
-> vmx_disable_intercept_for_msr()
-> pt_update_intercept_for_msr()
   -> vmx_set_intercept_for_msr()
      -> vmx_enable_intercept_for_msr()
      -> vmx_disable_intercept_for_msr()

Therefore, we exit early if !cpu_has_vmx_msr_bitmap().

Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>
---
 arch/x86/kvm/vmx/vmx.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 05319b74bd3d..5a866d3c2bc8 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4127,6 +4127,9 @@ static void vmx_msr_filter_changed(struct kvm_vcpu *vcpu)
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	u32 i;
 
+	if (!cpu_has_vmx_msr_bitmap())
+		return;
+
 	/*
 	 * Redo intercept permissions for MSRs that KVM is passing through to
 	 * the guest.  Disabling interception will check the new MSR filter and
-- 
2.34.1