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Subject[PATCH v2 09/13] KVM: SVM: include CR3 in initial VMSA state for SEV-ES guests
Date
Normally guests will set up CR3 themselves, but some guests, such as
kselftests, and potentially CONFIG_PVH guests, rely on being booted
with paging enabled and CR3 initialized to a pre-allocated page table.

Currently CR3 updates via KVM_SET_SREGS* are not loaded into the guest
VMCB until just prior to entering the guest. For SEV-ES/SEV-SNP, this
is too late, since it will have switched over to using the VMSA page
prior to that point, with the VMSA CR3 copied from the VMCB initial
CR3 value: 0.

Address this by sync'ing the CR3 value into the VMCB save area
immediately when KVM_SET_SREGS* is issued so it will find it's way into
the initial VMSA.

Suggested-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
arch/x86/include/asm/kvm-x86-ops.h | 1 +
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/svm/svm.c | 19 +++++++++++++++++++
arch/x86/kvm/vmx/vmx.c | 6 ++++++
arch/x86/kvm/x86.c | 1 +
5 files changed, 28 insertions(+)

diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index cefe1d81e2e8..a3172bd59690 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -35,6 +35,7 @@ KVM_X86_OP(get_cpl)
KVM_X86_OP(set_segment)
KVM_X86_OP_NULL(get_cs_db_l_bits)
KVM_X86_OP(set_cr0)
+KVM_X86_OP(post_set_cr3)
KVM_X86_OP(is_valid_cr4)
KVM_X86_OP(set_cr4)
KVM_X86_OP(set_efer)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d5fede05eb5f..22f384320ed1 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1342,6 +1342,7 @@ struct kvm_x86_ops {
struct kvm_segment *var, int seg);
void (*get_cs_db_l_bits)(struct kvm_vcpu *vcpu, int *db, int *l);
void (*set_cr0)(struct kvm_vcpu *vcpu, unsigned long cr0);
+ void (*post_set_cr3)(struct kvm_vcpu *vcpu, unsigned long cr3);
bool (*is_valid_cr4)(struct kvm_vcpu *vcpu, unsigned long cr0);
void (*set_cr4)(struct kvm_vcpu *vcpu, unsigned long cr4);
int (*set_efer)(struct kvm_vcpu *vcpu, u64 efer);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 208566f63bce..76e906d83a84 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1792,6 +1792,24 @@ static void svm_set_gdt(struct kvm_vcpu *vcpu, struct desc_ptr *dt)
vmcb_mark_dirty(svm->vmcb, VMCB_DT);
}

+static void svm_post_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+
+ /*
+ * For guests that don't set guest_state_protected, the cr3 update is
+ * handled via kvm_mmu_load() while entering the guest. For guests
+ * that do (SEV-ES/SEV-SNP), the cr3 update needs to be written to
+ * VMCB save area now, since the save area will become the initial
+ * contents of the VMSA, and future VMCB save area updates won't be
+ * seen.
+ */
+ if (sev_es_guest(vcpu->kvm)) {
+ svm->vmcb->save.cr3 = cr3;
+ vmcb_mark_dirty(svm->vmcb, VMCB_CR);
+ }
+}
+
void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
{
struct vcpu_svm *svm = to_svm(vcpu);
@@ -4622,6 +4640,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
.get_cpl = svm_get_cpl,
.get_cs_db_l_bits = kvm_get_cs_db_l_bits,
.set_cr0 = svm_set_cr0,
+ .post_set_cr3 = svm_post_set_cr3,
.is_valid_cr4 = svm_is_valid_cr4,
.set_cr4 = svm_set_cr4,
.set_efer = svm_set_efer,
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 63615d242bdf..075107c1b3f5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3124,6 +3124,11 @@ static void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa,
vmcs_writel(GUEST_CR3, guest_cr3);
}

+
+void vmx_post_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
+{
+}
+
static bool vmx_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
{
/*
@@ -7597,6 +7602,7 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
.get_cpl = vmx_get_cpl,
.get_cs_db_l_bits = vmx_get_cs_db_l_bits,
.set_cr0 = vmx_set_cr0,
+ .post_set_cr3 = vmx_post_set_cr3,
.is_valid_cr4 = vmx_is_valid_cr4,
.set_cr4 = vmx_set_cr4,
.set_efer = vmx_set_efer,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 26cb3a4cd0e9..c0d84a4c8049 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10609,6 +10609,7 @@ static int __set_sregs_common(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs,
*mmu_reset_needed |= kvm_read_cr3(vcpu) != sregs->cr3;
vcpu->arch.cr3 = sregs->cr3;
kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3);
+ static_call(kvm_x86_post_set_cr3)(vcpu, sregs->cr3);

kvm_set_cr8(vcpu, sregs->cr8);

--
2.25.1
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