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Subject[RFC PATCH 35/35] KVM: SVM: Provide support to launch and run an SEV-ES guest
Date
From: Tom Lendacky <thomas.lendacky@amd.com>

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@amd.com>
---
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
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