linux-kernel - [PATCH v3 09/10] KVM: TDX: Save and restore IA32

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Message-ID: <20250307212053.2948340-10-pbonzini@redhat.com>
Date: Fri,  7 Mar 2025 16:20:51 -0500
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc: xiaoyao.li@...el.com,
	adrian.hunter@...el.com,
	seanjc@...gle.com,
	rick.p.edgecombe@...el.com
Subject: [PATCH v3 09/10] KVM: TDX: Save and restore IA32_DEBUGCTL

From: Adrian Hunter <adrian.hunter@...el.com>

Save the IA32_DEBUGCTL MSR before entering a TDX VCPU and restore it
afterwards.  The TDX Module preserves bits 1, 12, and 14, so if no
other bits are set, no restore is done.

Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
Message-ID: <20250129095902.16391-12-adrian.hunter@...el.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/vmx/tdx.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 5625b0801ce8..25972e12504b 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -683,6 +683,8 @@ void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 	else
 		vt->msr_host_kernel_gs_base = read_msr(MSR_KERNEL_GS_BASE);
 
+	vt->host_debugctlmsr = get_debugctlmsr();
+
 	vt->guest_state_loaded = true;
 }
 
@@ -826,11 +828,15 @@ static void tdx_load_host_xsave_state(struct kvm_vcpu *vcpu)
 	if (kvm_host.xss != (kvm_tdx->xfam & kvm_caps.supported_xss))
 		wrmsrl(MSR_IA32_XSS, kvm_host.xss);
 }
-EXPORT_SYMBOL_GPL(kvm_load_host_xsave_state);
+
+#define TDX_DEBUGCTL_PRESERVED (DEBUGCTLMSR_BTF | \
+				DEBUGCTLMSR_FREEZE_PERFMON_ON_PMI | \
+				DEBUGCTLMSR_FREEZE_IN_SMM)
 
 fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 {
 	struct vcpu_tdx *tdx = to_tdx(vcpu);
+	struct vcpu_vt *vt = to_vt(vcpu);
 
 	/*
 	 * force_immediate_exit requires vCPU entering for events injection with
@@ -846,6 +852,9 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 
 	tdx_vcpu_enter_exit(vcpu);
 
+	if (vt->host_debugctlmsr & ~TDX_DEBUGCTL_PRESERVED)
+		update_debugctlmsr(vt->host_debugctlmsr);
+
 	tdx_load_host_xsave_state(vcpu);
 	tdx->guest_entered = true;
 
-- 
2.43.5