linux-kernel - [PATCH 10/28] KVM: nSVM: Don't initialize vmcb02 MSRPM with vmcb01's "always passthrough"

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Message-ID: <20250529234013.3826933-11-seanjc@google.com>
Date: Thu, 29 May 2025 16:39:55 -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, 
	Borislav Petkov <bp@...en8.de>, Xin Li <xin@...or.com>, Chao Gao <chao.gao@...el.com>, 
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: [PATCH 10/28] 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.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/nested.c | 1 -
 arch/x86/kvm/svm/svm.c    | 5 +++--
 arch/x86/kvm/svm/svm.h    | 1 -
 3 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index e4a079ea4b27..0026d2adb809 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1275,7 +1275,6 @@ 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 84dd1f220986..d97711bdbfc9 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -893,8 +893,9 @@ 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++) {
@@ -1403,7 +1404,7 @@ 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 0a8041d70994..47a36a9a7fe5 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -637,7 +637,6 @@ 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);
-- 
2.49.0.1204.g71687c7c1d-goog