[PATCH v19 080/130] KVM: TDX: restore host xsave state when exit from the guest TD

[isaku.yamahata@xxxxxxxxx]

From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

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

Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
---
v19:
- Add EXPORT_SYMBOL_GPL(host_xcr0)

v15 -> v16:
- Added CET flag mask

Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
---
 arch/x86/kvm/vmx/tdx.c | 19 +++++++++++++++++++
 arch/x86/kvm/x86.c     |  1 +
 2 files changed, 20 insertions(+)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 9616b1aab6ce..199226c6cf55 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -2,6 +2,7 @@
 #include <linux/cpu.h>
 #include <linux/mmu_context.h>
 
+#include <asm/fpu/xcr.h>
 #include <asm/tdx.h>
 
 #include "capabilities.h"
@@ -534,6 +535,23 @@ void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	 */
 }
 
+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) &&
+	    host_xcr0 != (kvm_tdx->xfam & kvm_caps.supported_xcr0))
+		xsetbv(XCR_XFEATURE_ENABLED_MASK, host_xcr0);
+	if (static_cpu_has(X86_FEATURE_XSAVES) &&
+	    /* PT can be exposed to TD guest regardless of KVM's XSS support */
+	    host_xss != (kvm_tdx->xfam &
+			 (kvm_caps.supported_xss | XFEATURE_MASK_PT | TDX_TD_XFAM_CET)))
+		wrmsrl(MSR_IA32_XSS, host_xss);
+	if (static_cpu_has(X86_FEATURE_PKU) &&
+	    (kvm_tdx->xfam & XFEATURE_MASK_PKRU))
+		write_pkru(vcpu->arch.host_pkru);
+}
+
 static noinstr void tdx_vcpu_enter_exit(struct vcpu_tdx *tdx)
 {
 	struct tdx_module_args args;
@@ -609,6 +627,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
 
 	tdx_vcpu_enter_exit(tdx);
 
+	tdx_restore_host_xsave_state(vcpu);
 	tdx->host_state_need_restore = true;
 
 	vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 23ece956c816..b361d948140f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -315,6 +315,7 @@ const struct kvm_stats_header kvm_vcpu_stats_header = {
 };
 
 u64 __read_mostly host_xcr0;
+EXPORT_SYMBOL_GPL(host_xcr0);
 
 static struct kmem_cache *x86_emulator_cache;
 
-- 
2.25.1