Re: [PATCH v2 09/13] KVM: SVM: include CR3 in initial VMSA state for SEV-ES guests

Paolo Bonzini <pbonzini@xxxxxxxxxx> · Wed, 22 Dec 2021 15:25:32 +0100

On 12/16/21 18:13, Michael Roth wrote:
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@xxxxxxx>
Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
---
  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);
  


I'm going to apply this one now, just with a small change to avoid 
vmx_post_set_cr3 and a remark about why kvm_set_cr3 is not calling the 
new hook.

diff --git a/arch/x86/include/asm/kvm-x86-ops.h 
b/arch/x86/include/asm/kvm-x86-ops.h
index 8803773539a0..37624a9e3e40 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -35,7 +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_NULL(post_set_cr3)
 KVM_X86_OP(is_valid_cr4)
 KVM_X86_OP(set_cr4)
 KVM_X86_OP(set_efer)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index a39da103e33c..fe06b02994e6 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3135,10 +3135,6 @@ static void vmx_load_mmu_pgd(struct kvm_vcpu 
*vcpu, hpa_t root_hpa,
 }


-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)
 {
 	/*
@@ -7608,7 +7604,6 @@ 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 db118066c653..c194a8cbd25f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1179,6 +1179,7 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned 
long cr3)

 	vcpu->arch.cr3 = cr3;
 	kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3);
+	/* Do not call post_set_cr3, we do not get here for confidential 
guests.  */

 handle_tlb_flush:
 	/*
@@ -10636,7 +10637,7 @@ 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);
+	static_call_cond(kvm_x86_post_set_cr3)(vcpu, sregs->cr3);

 	kvm_set_cr8(vcpu, sregs->cr8);

Paolo







