From: Sean Christopherson <seanjc@google.com>
Date: Tue, 10 Jun 2025 22:57:17 +0000 (-0700)
Subject: KVM: nSVM: Don't initialize vmcb02 MSRPM with vmcb01's "always passthrough"
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4879dc9469e6d54d1199b3c53f7c16c891d9004f;p=thirdparty%2Flinux.git

KVM: nSVM: Don't initialize vmcb02 MSRPM with vmcb01's "always passthrough"

Don't initialize vmcb02's MSRPM with KVM's set of "always passthrough"
MSRs, as KVM always needs to consult L1's intercepts, i.e. needs to merge
vmcb01 with vmcb12 and write the result to vmcb02.  This will eventually
allow for the removal of svm_vcpu_init_msrpm().

Note, the bitmaps are truly initialized by svm_vcpu_alloc_msrpm() (default
to intercepting all MSRs), e.g. if there is a bug lurking elsewhere, the
worst case scenario from dropping the call to svm_vcpu_init_msrpm() should
be that KVM would fail to passthrough MSRs to L2.

Link: https://lore.kernel.org/r/20250610225737.156318-13-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
---

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 360dbd80a7288..cf148f7db8876 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1285,7 +1285,6 @@ int svm_allocate_nested(struct vcpu_svm *svm)
 	svm->nested.msrpm = svm_vcpu_alloc_msrpm();
 	if (!svm->nested.msrpm)
 		goto err_free_vmcb02;
-	svm_vcpu_init_msrpm(&svm->vcpu, svm->nested.msrpm);
 
 	svm->nested.initialized = true;
 	return 0;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index d8b67bedf183a..290862b27aedb 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -883,8 +883,9 @@ u32 *svm_vcpu_alloc_msrpm(void)
 	return msrpm;
 }
 
-void svm_vcpu_init_msrpm(struct kvm_vcpu *vcpu, u32 *msrpm)
+static void svm_vcpu_init_msrpm(struct kvm_vcpu *vcpu)
 {
+	u32 *msrpm = to_svm(vcpu)->msrpm;
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(direct_access_msrs); i++) {
@@ -1396,7 +1397,7 @@ static void __svm_vcpu_reset(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
-	svm_vcpu_init_msrpm(vcpu, svm->msrpm);
+	svm_vcpu_init_msrpm(vcpu);
 
 	svm_init_osvw(vcpu);
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 9f750b2399e92..bce66afafa112 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -633,7 +633,6 @@ extern bool dump_invalid_vmcb;
 
 u32 svm_msrpm_offset(u32 msr);
 u32 *svm_vcpu_alloc_msrpm(void);
-void svm_vcpu_init_msrpm(struct kvm_vcpu *vcpu, u32 *msrpm);
 void svm_vcpu_free_msrpm(u32 *msrpm);
 void svm_copy_lbrs(struct vmcb *to_vmcb, struct vmcb *from_vmcb);
 void svm_enable_lbrv(struct kvm_vcpu *vcpu);