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Subject[RFC PATCH 33/35] KVM: SVM: Provide support for SEV-ES vCPU loading
Date
From: Tom Lendacky <thomas.lendacky@amd.com>

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
VMRUM (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 value of XCR0 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>
---
arch/x86/kvm/svm/sev.c | 48 ++++++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/svm/svm.c | 36 +++++++++++++++++++------------
arch/x86/kvm/svm/svm.h | 22 +++++++++++++------
3 files changed, 87 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 7ed88f2e8d93..50018436863b 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -17,11 +17,14 @@
#include <linux/trace_events.h>

#include <asm/trapnr.h>
+#include <asm/fpu/internal.h>

#include "x86.h"
#include "svm.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);
@@ -1599,3 +1602,48 @@ 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
+ * saved via the vmsave above.
+ */
+ 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);
+}
+
+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]);
+ }
+}
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index cb9b1d281adb..efefe8ba9759 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1340,15 +1340,20 @@ 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;
@@ -1376,19 +1381,24 @@ 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)
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 465e14a7146f..0812d70085d7 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/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 MSRPM_OFFSETS 16
@@ -573,6 +581,8 @@ int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in);
void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector);
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);

/* VMSA Accessor functions */

--
2.28.0
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