[RFC PATCH 35/35] KVM: SVM: Provide support to launch and run an SEV-ES guest

[Tom Lendacky]

From: Tom Lendacky <thomas.lendacky@xxxxxxx>

An SEV-ES guest requires some additional steps to be launched as compared
to an SEV guest:
  - Implement additional VMCB initialization requirements for SEV-ES.
  - Update MSR_VM_HSAVE_PA to include the encryption bit if SME is active.
  - Add additional MSRs to the list of direct access MSRs so that the
    intercepts can be disabled.
  - Measure all vCPUs using the LAUNCH_UPDATE_VMSA SEV command after all
    calls to LAUNCH_UPDATE_DATA have been performed but before the call
    to LAUNCH_MEASURE has been performed.
  - Use VMSAVE to save host information that is not saved on VMRUN but is
    restored on VMEXIT.
  - Modify the VMRUN path to eliminate guest register state restoring and
    saving.

At this point the guest can be run. However, the run sequence is different
for an SEV-ES guest compared to a normal or even an SEV guest. Because the
guest register state is encrypted, it is all saved as part of VMRUN/VMEXIT
and does not require restoring before or saving after a VMRUN instruction.
As a result, all that is required to perform a VMRUN is to save the RBP
and RAX registers, issue the VMRUN and then restore RAX and RBP.

Additionally, certain state is automatically saved and restored with an
SEV-ES VMRUN. As a result certain register states are not required to be
restored upon VMEXIT (e.g. FS, GS, etc.), so only do that if the guest is
not an SEV-ES guest.

Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
 arch/x86/kvm/svm/sev.c | 60 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 50018436863b..eaa669c16345 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -201,6 +201,16 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	return ret;
 }
 
+static int sev_es_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
+{
+	if (!sev_es)
+		return -ENOTTY;
+
+	to_kvm_svm(kvm)->sev_info.es_active = true;
+
+	return sev_guest_init(kvm, argp);
+}
+
 static int sev_bind_asid(struct kvm *kvm, unsigned int handle, int *error)
 {
 	struct sev_data_activate *data;
@@ -501,6 +511,50 @@ static int sev_launch_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	return ret;
 }
 
+static int sev_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
+{
+	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+	struct sev_data_launch_update_vmsa *vmsa;
+	int i, ret;
+
+	if (!sev_es_guest(kvm))
+		return -ENOTTY;
+
+	vmsa = kzalloc(sizeof(*vmsa), GFP_KERNEL);
+	if (!vmsa)
+		return -ENOMEM;
+
+	for (i = 0; i < kvm->created_vcpus; i++) {
+		struct vcpu_svm *svm = to_svm(kvm->vcpus[i]);
+		struct vmcb_save_area *save = get_vmsa(svm);
+
+		/* Set XCR0 before encrypting */
+		save->xcr0 = svm->vcpu.arch.xcr0;
+
+		/*
+		 * The LAUNCH_UPDATE_VMSA command will perform in-place
+		 * encryption of the VMSA memory content (i.e it will write
+		 * the same memory region with the guest's key), so invalidate
+		 * it first.
+		 */
+		clflush_cache_range(svm->vmsa, PAGE_SIZE);
+
+		vmsa->handle = sev->handle;
+		vmsa->address = __sme_pa(svm->vmsa);
+		vmsa->len = PAGE_SIZE;
+		ret = sev_issue_cmd(kvm, SEV_CMD_LAUNCH_UPDATE_VMSA, vmsa,
+				    &argp->error);
+		if (ret)
+			goto e_free;
+
+		svm->vcpu.arch.vmsa_encrypted = true;
+	}
+
+e_free:
+	kfree(vmsa);
+	return ret;
+}
+
 static int sev_launch_measure(struct kvm *kvm, struct kvm_sev_cmd *argp)
 {
 	void __user *measure = (void __user *)(uintptr_t)argp->data;
@@ -948,12 +1002,18 @@ int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
 	case KVM_SEV_INIT:
 		r = sev_guest_init(kvm, &sev_cmd);
 		break;
+	case KVM_SEV_ES_INIT:
+		r = sev_es_guest_init(kvm, &sev_cmd);
+		break;
 	case KVM_SEV_LAUNCH_START:
 		r = sev_launch_start(kvm, &sev_cmd);
 		break;
 	case KVM_SEV_LAUNCH_UPDATE_DATA:
 		r = sev_launch_update_data(kvm, &sev_cmd);
 		break;
+	case KVM_SEV_LAUNCH_UPDATE_VMSA:
+		r = sev_launch_update_vmsa(kvm, &sev_cmd);
+		break;
 	case KVM_SEV_LAUNCH_MEASURE:
 		r = sev_launch_measure(kvm, &sev_cmd);
 		break;
-- 
2.28.0