linux-kernel - [PATCH v12 05/24] KVM: x86: Zero XSTATE components on INIT by iterating over supported features

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Message-ID: <20250812025606.74625-6-chao.gao@intel.com>
Date: Mon, 11 Aug 2025 19:55:13 -0700
From: Chao Gao <chao.gao@...el.com>
To: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: mlevitsk@...hat.com,
	rick.p.edgecombe@...el.com,
	weijiang.yang@...el.com,
	xin@...or.com,
	Chao Gao <chao.gao@...el.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Mathias Krause <minipli@...ecurity.net>,
	John Allen <john.allen@....com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	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,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH v12 05/24] KVM: x86: Zero XSTATE components on INIT by iterating over supported features

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

No functional change intended.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Tested-by: Mathias Krause <minipli@...ecurity.net>
Tested-by: John Allen <john.allen@....com>
Signed-off-by: Chao Gao <chao.gao@...el.com>
---
 arch/x86/kvm/x86.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6cf0d15a7a64..0010aa45bf9f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12392,6 +12392,8 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
 static void kvm_xstate_reset(struct kvm_vcpu *vcpu, bool init_event)
 {
 	struct fpstate *fpstate = vcpu->arch.guest_fpu.fpstate;
+	u64 xfeatures_mask;
+	int i;
 
 	/*
 	 * Guest FPU state is zero allocated and so doesn't need to be manually
@@ -12405,16 +12407,20 @@ static void kvm_xstate_reset(struct kvm_vcpu *vcpu, bool init_event)
 	 * are unchanged.  Currently, the only components that are zeroed and
 	 * supported by KVM are MPX related.
 	 */
-	if (!kvm_mpx_supported())
+	xfeatures_mask = (kvm_caps.supported_xcr0 | kvm_caps.supported_xss) &
+			 (XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR);
+	if (!xfeatures_mask)
 		return;
 
+	BUILD_BUG_ON(sizeof(xfeatures_mask) * BITS_PER_BYTE <= XFEATURE_MAX);
+
 	/*
 	 * All paths that lead to INIT are required to load the guest's FPU
 	 * state (because most paths are buried in KVM_RUN).
 	 */
 	kvm_put_guest_fpu(vcpu);
-	fpstate_clear_xstate_component(fpstate, XFEATURE_BNDREGS);
-	fpstate_clear_xstate_component(fpstate, XFEATURE_BNDCSR);
+	for_each_set_bit(i, (unsigned long *)&xfeatures_mask, XFEATURE_MAX)
+		fpstate_clear_xstate_component(fpstate, i);
 	kvm_load_guest_fpu(vcpu);
 }
 
-- 
2.47.1