Commit f8d808ed authored by Sean Christopherson's avatar Sean Christopherson
Browse files

KVM: SVM: Rewrite sev_es_prepare_switch_to_guest()'s comment about swap types 



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: default avatarAlexey Kardashevskiy <aik@amd.com>
Link: https://lore.kernel.org/r/20230615063757.3039121-4-aik@amd.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 29de732c

arch/x86/kvm/svm/sev.c

+15 −10
Original line number Diff line number Diff line
@@ -3023,19 +3023,24 @@ 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;

}