linux-kernel - [PATCH v8 10/26] KVM: x86: Refine xsave-managed guest register/MSR reset handling

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Message-Id: <20231221140239.4349-11-weijiang.yang@intel.com>
Date: Thu, 21 Dec 2023 09:02:23 -0500
From: Yang Weijiang <weijiang.yang@...el.com>
To: seanjc@...gle.com,
	pbonzini@...hat.com,
	dave.hansen@...el.com,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: peterz@...radead.org,
	chao.gao@...el.com,
	rick.p.edgecombe@...el.com,
	mlevitsk@...hat.com,
	john.allen@....com,
	weijiang.yang@...el.com
Subject: [PATCH v8 10/26] KVM: x86: Refine xsave-managed guest register/MSR reset handling

Tweak the code a bit to facilitate resetting more xstate components in
the future, e.g., adding CET's xstate-managed MSRs.

No functional change intended.

Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/x86.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0e7dc3398293..3671f4868d1b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12205,6 +12205,11 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
 		static_branch_dec(&kvm_has_noapic_vcpu);
 }
 
+static inline bool is_xstate_reset_needed(void)
+{
+	return kvm_cpu_cap_has(X86_FEATURE_MPX);
+}
+
 void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 {
 	struct kvm_cpuid_entry2 *cpuid_0x1;
@@ -12262,7 +12267,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	kvm_async_pf_hash_reset(vcpu);
 	vcpu->arch.apf.halted = false;
 
-	if (vcpu->arch.guest_fpu.fpstate && kvm_mpx_supported()) {
+	if (vcpu->arch.guest_fpu.fpstate && is_xstate_reset_needed()) {
 		struct fpstate *fpstate = vcpu->arch.guest_fpu.fpstate;
 
 		/*
@@ -12272,8 +12277,12 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 		if (init_event)
 			kvm_put_guest_fpu(vcpu);
 
-		fpstate_clear_xstate_component(fpstate, XFEATURE_BNDREGS);
-		fpstate_clear_xstate_component(fpstate, XFEATURE_BNDCSR);
+		if (kvm_cpu_cap_has(X86_FEATURE_MPX)) {
+			fpstate_clear_xstate_component(fpstate,
+						       XFEATURE_BNDREGS);
+			fpstate_clear_xstate_component(fpstate,
+						       XFEATURE_BNDCSR);
+		}
 
 		if (init_event)
 			kvm_load_guest_fpu(vcpu);
-- 
2.39.3