Commit ebd1a336 authored by Sean Christopherson's avatar Sean Christopherson
Browse files

KVM: SVM: Handle #MCs in guest outside of fastpath 



Handle Machine Checks (#MC) that happen in the guest (by forwarding them
to the host) outside of KVM's fastpath so that as much host state as
possible is re-loaded before invoking the kernel's #MC handler.  The only
requirement is that KVM invokes the #MC handler before enabling IRQs (and
even that could _probably_ be relaxed to handling #MCs before enabling
preemption).

Waiting to handle #MCs until "more" host state is loaded hardens KVM
against flaws in the #MC handler, which has historically been quite
brittle. E.g. prior to commit 5567d11c ("x86/mce: Send #MC singal from
task work"), the #MC code could trigger a schedule() with IRQs and
preemption disabled.  That led to a KVM hack-a-fix in commit 1811d979
("x86/kvm: move kvm_load/put_guest_xcr0 into atomic context").

Note, except for #MCs on VM-Enter, VMX already handles #MCs outside of the
fastpath.

Reviewed-by: default avatarRick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: default avatarJon Kohler <jon@nutanix.com>
Link: https://patch.msgid.link/20251118222328.2265758-2-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 38ee66cb

arch/x86/kvm/svm/svm.c

+9 −9
Original line number Diff line number Diff line
@@ -4325,14 +4325,6 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags) 


	vcpu->arch.regs_avail &= ~SVM_REGS_LAZY_LOAD_SET;



	/*

	 * We need to handle MC intercepts here before the vcpu has a chance to

	 * change the physical cpu

	 */

	if (unlikely(svm->vmcb->control.exit_code ==

		     SVM_EXIT_EXCP_BASE + MC_VECTOR))

		svm_handle_mce(vcpu);



	trace_kvm_exit(vcpu, KVM_ISA_SVM);



	svm_complete_interrupts(vcpu);
@@ -4621,8 +4613,16 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu, 


static void svm_handle_exit_irqoff(struct kvm_vcpu *vcpu)

{

	if (to_svm(vcpu)->vmcb->control.exit_code == SVM_EXIT_INTR)

	switch (to_svm(vcpu)->vmcb->control.exit_code) {

	case SVM_EXIT_EXCP_BASE + MC_VECTOR:

		svm_handle_mce(vcpu);

		break;

	case SVM_EXIT_INTR:

		vcpu->arch.at_instruction_boundary = true;

		break;

	default:

		break;

	}

}



static void svm_setup_mce(struct kvm_vcpu *vcpu)