KVM: SVM: Provide support for SEV-ES vCPU loading

An SEV-ES vCPU requires additional VMCB vCPU load/put requirements. SEV-ES
hardware will restore certain registers on VMEXIT, but not save them on
VMRUN (see Table B-3 and Table B-4 of the AMD64 APM Volume 2), so make the
following changes:

General vCPU load changes:
  - During vCPU loading, perform a VMSAVE to the per-CPU SVM save area and
    save the current values of XCR0, XSS and PKRU to the per-CPU SVM save
    area as these registers will be restored on VMEXIT.

General vCPU put changes:
  - Do not attempt to restore registers that SEV-ES hardware has already
    restored on VMEXIT.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <019390e9cb5e93cd73014fa5a040c17d42588733.1607620209.git.thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/svm.h

@@ -234,7 +234,8 @@ struct vmcb_save_area {
 	u8 cpl;
 	u8 reserved_2[4];
 	u64 efer;
-	u8 reserved_3[112];
+	u8 reserved_3[104];
+	u64 xss;		/* Valid for SEV-ES only */
 	u64 cr4;
 	u64 cr3;
 	u64 cr0;
@@ -265,9 +266,12 @@ struct vmcb_save_area {
 
 	/*
 	 * The following part of the save area is valid only for
-	 * SEV-ES guests when referenced through the GHCB.
+	 * SEV-ES guests when referenced through the GHCB or for
+	 * saving to the host save area.
 	 */
-	u8 reserved_7[104];
+	u8 reserved_7[80];
+	u32 pkru;
+	u8 reserved_7a[20];
 	u64 reserved_8;		/* rax already available at 0x01f8 */
 	u64 rcx;
 	u64 rdx;

arch/x86/kvm/svm/sev.c

@@ -16,12 +16,15 @@
 #include <linux/swap.h>
 #include <linux/processor.h>
 #include <linux/trace_events.h>
+#include <asm/fpu/internal.h>
 
 #include "x86.h"
 #include "svm.h"
 #include "cpuid.h"
 #include "trace.h"
 
+#define __ex(x) __kvm_handle_fault_on_reboot(x)
+
 static u8 sev_enc_bit;
 static int sev_flush_asids(void);
 static DECLARE_RWSEM(sev_deactivate_lock);
@@ -1852,3 +1855,54 @@ void sev_es_create_vcpu(struct vcpu_svm *svm)
 					    GHCB_VERSION_MIN,
 					    sev_enc_bit));
 }
+
+void sev_es_vcpu_load(struct vcpu_svm *svm, int cpu)
+{
+	struct svm_cpu_data *sd = per_cpu(svm_data, cpu);
+	struct vmcb_save_area *hostsa;
+	unsigned int i;
+
+	/*
+	 * As an SEV-ES guest, hardware will restore the host state on VMEXIT,
+	 * of which one step is to perform a VMLOAD. Since hardware does not
+	 * perform a VMSAVE on VMRUN, the host savearea must be updated.
+	 */
+	asm volatile(__ex("vmsave") : : "a" (__sme_page_pa(sd->save_area)) : "memory");
+
+	/*
+	 * Certain MSRs are restored on VMEXIT, only save ones that aren't
+	 * restored.
+	 */
+	for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++) {
+		if (host_save_user_msrs[i].sev_es_restored)
+			continue;
+
+		rdmsrl(host_save_user_msrs[i].index, svm->host_user_msrs[i]);
+	}
+
+	/* XCR0 is restored on VMEXIT, save the current host value */
+	hostsa = (struct vmcb_save_area *)(page_address(sd->save_area) + 0x400);
+	hostsa->xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
+
+	/* PKRU is restored on VMEXIT, save the curent host value */
+	hostsa->pkru = read_pkru();
+
+	/* MSR_IA32_XSS is restored on VMEXIT, save the currnet host value */
+	hostsa->xss = host_xss;
+}
+
+void sev_es_vcpu_put(struct vcpu_svm *svm)
+{
+	unsigned int i;
+
+	/*
+	 * Certain MSRs are restored on VMEXIT and were saved with vmsave in
+	 * sev_es_vcpu_load() above. Only restore ones that weren't.
+	 */
+	for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++) {
+		if (host_save_user_msrs[i].sev_es_restored)
+			continue;
+
+		wrmsrl(host_save_user_msrs[i].index, svm->host_user_msrs[i]);
+	}
+}

arch/x86/kvm/svm/svm.c

@@ -1417,15 +1417,20 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 		vmcb_mark_all_dirty(svm->vmcb);
 	}
 
+	if (sev_es_guest(svm->vcpu.kvm)) {
+		sev_es_vcpu_load(svm, cpu);
+	} else {
 #ifdef CONFIG_X86_64
-	rdmsrl(MSR_GS_BASE, to_svm(vcpu)->host.gs_base);
+		rdmsrl(MSR_GS_BASE, to_svm(vcpu)->host.gs_base);
 #endif
-	savesegment(fs, svm->host.fs);
-	savesegment(gs, svm->host.gs);
-	svm->host.ldt = kvm_read_ldt();
+		savesegment(fs, svm->host.fs);
+		savesegment(gs, svm->host.gs);
+		svm->host.ldt = kvm_read_ldt();
 
-	for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++)
-		rdmsrl(host_save_user_msrs[i], svm->host_user_msrs[i]);
+		for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++)
+			rdmsrl(host_save_user_msrs[i].index,
+			       svm->host_user_msrs[i]);
+	}
 
 	if (static_cpu_has(X86_FEATURE_TSCRATEMSR)) {
 		u64 tsc_ratio = vcpu->arch.tsc_scaling_ratio;
@@ -1453,19 +1458,24 @@ static void svm_vcpu_put(struct kvm_vcpu *vcpu)
 	avic_vcpu_put(vcpu);
 
 	++vcpu->stat.host_state_reload;
-	kvm_load_ldt(svm->host.ldt);
+	if (sev_es_guest(svm->vcpu.kvm)) {
+		sev_es_vcpu_put(svm);
+	} else {
+		kvm_load_ldt(svm->host.ldt);
 #ifdef CONFIG_X86_64
-	loadsegment(fs, svm->host.fs);
-	wrmsrl(MSR_KERNEL_GS_BASE, current->thread.gsbase);
-	load_gs_index(svm->host.gs);
+		loadsegment(fs, svm->host.fs);
+		wrmsrl(MSR_KERNEL_GS_BASE, current->thread.gsbase);
+		load_gs_index(svm->host.gs);
 #else
 #ifdef CONFIG_X86_32_LAZY_GS
-	loadsegment(gs, svm->host.gs);
+		loadsegment(gs, svm->host.gs);
 #endif
 #endif
 
-	for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++)
-		wrmsrl(host_save_user_msrs[i], svm->host_user_msrs[i]);
+		for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++)
+			wrmsrl(host_save_user_msrs[i].index,
+			       svm->host_user_msrs[i]);
+	}
 }
 
 static unsigned long svm_get_rflags(struct kvm_vcpu *vcpu)

arch/x86/kvm/svm/svm.h

@@ -23,15 +23,23 @@
 
 #define __sme_page_pa(x) __sme_set(page_to_pfn(x) << PAGE_SHIFT)
 
-static const u32 host_save_user_msrs[] = {
+static const struct svm_host_save_msrs {
+	u32 index;		/* Index of the MSR */
+	bool sev_es_restored;	/* True if MSR is restored on SEV-ES VMEXIT */
+} host_save_user_msrs[] = {
 #ifdef CONFIG_X86_64
-	MSR_STAR, MSR_LSTAR, MSR_CSTAR, MSR_SYSCALL_MASK, MSR_KERNEL_GS_BASE,
-	MSR_FS_BASE,
+	{ .index = MSR_STAR,			.sev_es_restored = true },
+	{ .index = MSR_LSTAR,			.sev_es_restored = true },
+	{ .index = MSR_CSTAR,			.sev_es_restored = true },
+	{ .index = MSR_SYSCALL_MASK,		.sev_es_restored = true },
+	{ .index = MSR_KERNEL_GS_BASE,		.sev_es_restored = true },
+	{ .index = MSR_FS_BASE,			.sev_es_restored = true },
 #endif
-	MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
-	MSR_TSC_AUX,
+	{ .index = MSR_IA32_SYSENTER_CS,	.sev_es_restored = true },
+	{ .index = MSR_IA32_SYSENTER_ESP,	.sev_es_restored = true },
+	{ .index = MSR_IA32_SYSENTER_EIP,	.sev_es_restored = true },
+	{ .index = MSR_TSC_AUX,			.sev_es_restored = false },
 };
-
 #define NR_HOST_SAVE_USER_MSRS ARRAY_SIZE(host_save_user_msrs)
 
 #define MAX_DIRECT_ACCESS_MSRS	18
@@ -580,5 +588,7 @@ int sev_handle_vmgexit(struct vcpu_svm *svm);
 int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in);
 void sev_es_init_vmcb(struct vcpu_svm *svm);
 void sev_es_create_vcpu(struct vcpu_svm *svm);
+void sev_es_vcpu_load(struct vcpu_svm *svm, int cpu);
+void sev_es_vcpu_put(struct vcpu_svm *svm);
 
 #endif

arch/x86/kvm/x86.c

@@ -197,7 +197,8 @@ EXPORT_SYMBOL_GPL(host_efer);
 bool __read_mostly allow_smaller_maxphyaddr = 0;
 EXPORT_SYMBOL_GPL(allow_smaller_maxphyaddr);
 
-static u64 __read_mostly host_xss;
+u64 __read_mostly host_xss;
+EXPORT_SYMBOL_GPL(host_xss);
 u64 __read_mostly supported_xss;
 EXPORT_SYMBOL_GPL(supported_xss);
 

arch/x86/kvm/x86.h

@@ -279,6 +279,7 @@ fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu);
 
 extern u64 host_xcr0;
 extern u64 supported_xcr0;
+extern u64 host_xss;
 extern u64 supported_xss;
 
 static inline bool kvm_mpx_supported(void)