From: Sean Christopherson <seanjc@xxxxxxxxxx>
Rewrite the comment(s) in sev_es_prepare_switch_to_guest() to explain the
swap types employed by the CPU for SEV-ES guests, i.e. to explain why KVM
needs to save a seemingly random subset of host state, and to provide a
decoder for the APM's Type-A/B/C terminology.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxx>
---
Changes:
v6:
* new to the series
---
arch/x86/kvm/svm/sev.c | 25 ++++++++++++--------
1 file changed, 15 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index c03bd063aecf..36fe2fcb4698 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3020,19 +3020,24 @@ void sev_es_vcpu_reset(struct vcpu_svm *svm)
void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa)
{
/*
- * As an SEV-ES guest, hardware will restore the host state on VMEXIT,
- * of which one step is to perform a VMLOAD. KVM performs the
- * corresponding VMSAVE in svm_prepare_guest_switch for both
- * traditional and SEV-ES guests.
+ * All host state for SEV-ES guests is categorized into three swap types
+ * based on how it is handled by hardware during a world switch:
+ *
+ * A: VMRUN: Host state saved in host save area
+ * VMEXIT: Host state loaded from host save area
+ *
+ * B: VMRUN: Host state _NOT_ saved in host save area
+ * VMEXIT: Host state loaded from host save area
+ *
+ * C: VMRUN: Host state _NOT_ saved in host save area
+ * VMEXIT: Host state initialized to default(reset) values
+ *
+ * Manually save type-B state, i.e. state that is loaded by VMEXIT but
+ * isn't saved by VMRUN, that isn't already saved by VMSAVE (performed
+ * by common SVM code).
*/
-
- /* XCR0 is restored on VMEXIT, save the current host value */
hostsa->xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
-
- /* PKRU is restored on VMEXIT, save the current host value */
hostsa->pkru = read_pkru();
-
- /* MSR_IA32_XSS is restored on VMEXIT, save the currnet host value */
hostsa->xss = host_xss;
}
--
2.40.1
