linux-kernel - [PATCH 4/7] KVM: TDX: restore host xsave state when exit from the guest TD

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Message-ID: <20241121201448.36170-5-adrian.hunter@intel.com>
Date: Thu, 21 Nov 2024 22:14:43 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com,
	kvm@...r.kernel.org,
	dave.hansen@...ux.intel.com
Cc: rick.p.edgecombe@...el.com,
	kai.huang@...el.com,
	adrian.hunter@...el.com,
	reinette.chatre@...el.com,
	xiaoyao.li@...el.com,
	tony.lindgren@...ux.intel.com,
	binbin.wu@...ux.intel.com,
	dmatlack@...gle.com,
	isaku.yamahata@...el.com,
	nik.borisov@...e.com,
	linux-kernel@...r.kernel.org,
	x86@...nel.org,
	yan.y.zhao@...el.com,
	chao.gao@...el.com,
	weijiang.yang@...el.com
Subject: [PATCH 4/7] KVM: TDX: restore host xsave state when exit from the guest TD

From: Isaku Yamahata <isaku.yamahata@...el.com>

On exiting from the guest TD, xsave state is clobbered.  Restore xsave
state on TD exit.

Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
TD vcpu enter/exit v1:
- Remove noinstr on tdx_vcpu_enter_exit() (Sean)
- Switch to kvm_host struct for xcr0 and xss

v19:
- Add EXPORT_SYMBOL_GPL(host_xcr0)

v15 -> v16:
- Added CET flag mask
---
 arch/x86/kvm/vmx/tdx.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 6e4ea2d420bc..00fdd2932205 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -2,6 +2,8 @@
 #include <linux/cleanup.h>
 #include <linux/cpu.h>
 #include <linux/mmu_context.h>
+
+#include <asm/fpu/xcr.h>
 #include <asm/tdx.h>
 #include "capabilities.h"
 #include "mmu.h"
@@ -709,6 +711,24 @@ void tdx_vcpu_free(struct kvm_vcpu *vcpu)
 }
 
 
+static void tdx_restore_host_xsave_state(struct kvm_vcpu *vcpu)
+{
+	struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
+
+	if (static_cpu_has(X86_FEATURE_XSAVE) &&
+	    kvm_host.xcr0 != (kvm_tdx->xfam & kvm_caps.supported_xcr0))
+		xsetbv(XCR_XFEATURE_ENABLED_MASK, kvm_host.xcr0);
+	if (static_cpu_has(X86_FEATURE_XSAVES) &&
+	    /* PT can be exposed to TD guest regardless of KVM's XSS support */
+	    kvm_host.xss != (kvm_tdx->xfam &
+			 (kvm_caps.supported_xss | XFEATURE_MASK_PT |
+			  XFEATURE_MASK_CET_USER | XFEATURE_MASK_CET_KERNEL)))
+		wrmsrl(MSR_IA32_XSS, kvm_host.xss);
+	if (static_cpu_has(X86_FEATURE_PKU) &&
+	    (kvm_tdx->xfam & XFEATURE_MASK_PKRU))
+		write_pkru(vcpu->arch.host_pkru);
+}
+
 static void tdx_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_tdx *tdx = to_tdx(vcpu);
@@ -776,6 +796,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 
 	tdx_vcpu_enter_exit(vcpu);
 
+	tdx_restore_host_xsave_state(vcpu);
 	tdx->host_state_need_restore = true;
 
 	vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
-- 
2.43.0