Commit beb8d93b authored Apr 19, 2019 by Sean Christopherson Committed by Paolo Bonzini Jun 18, 2019

KVM: VMX: Fix handling of #MC that occurs during VM-Entry



A previous fix to prevent KVM from consuming stale VMCS state after a
failed VM-Entry inadvertantly blocked KVM's handling of machine checks
that occur during VM-Entry.

Per Intel's SDM, a #MC during VM-Entry is handled in one of three ways,
depending on when the #MC is recognoized.  As it pertains to this bug
fix, the third case explicitly states EXIT_REASON_MCE_DURING_VMENTRY
is handled like any other VM-Exit during VM-Entry, i.e. sets bit 31 to
indicate the VM-Entry failed.

If a machine-check event occurs during a VM entry, one of the following occurs:
 - The machine-check event is handled as if it occurred before the VM entry:
        ...
 - The machine-check event is handled after VM entry completes:
        ...
 - A VM-entry failure occurs as described in Section 26.7. The basic
   exit reason is 41, for "VM-entry failure due to machine-check event".

Explicitly handle EXIT_REASON_MCE_DURING_VMENTRY as a one-off case in
vmx_vcpu_run() instead of binning it into vmx_complete_atomic_exit().
Doing so allows vmx_vcpu_run() to handle VMX_EXIT_REASONS_FAILED_VMENTRY
in a sane fashion and also simplifies vmx_complete_atomic_exit() since
VMCS.VM_EXIT_INTR_INFO is guaranteed to be fresh.

Fixes: b060ca3b ("kvm: vmx: Handle VMLAUNCH/VMRESUME failure properly")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 73f624f4

arch/x86/kvm/vmx/vmx.c

+8 −12

Original line number	Diff line number	Diff line
		@@ -6107,28 +6107,21 @@ static void vmx_apicv_post_state_restore(struct kvm_vcpu *vcpu)

		static void vmx_complete_atomic_exit(struct vcpu_vmx *vmx)
		{
		u32 exit_intr_info = 0;
		u16 basic_exit_reason = (u16)vmx->exit_reason;

		if (!(basic_exit_reason == EXIT_REASON_MCE_DURING_VMENTRY
		\|\| basic_exit_reason == EXIT_REASON_EXCEPTION_NMI))
		if (vmx->exit_reason != EXIT_REASON_EXCEPTION_NMI)
		return;

		if (!(vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
		exit_intr_info = vmcs_read32(VM_EXIT_INTR_INFO);
		vmx->exit_intr_info = exit_intr_info;
		vmx->exit_intr_info = vmcs_read32(VM_EXIT_INTR_INFO);

		/* if exit due to PF check for async PF */
		if (is_page_fault(exit_intr_info))
		if (is_page_fault(vmx->exit_intr_info))
		vmx->vcpu.arch.apf.host_apf_reason = kvm_read_and_reset_pf_reason();

		/* Handle machine checks before interrupts are enabled */
		if (basic_exit_reason == EXIT_REASON_MCE_DURING_VMENTRY \|\|
		is_machine_check(exit_intr_info))
		if (is_machine_check(vmx->exit_intr_info))
		kvm_machine_check();

		/* We need to handle NMIs before interrupts are enabled */
		if (is_nmi(exit_intr_info)) {
		if (is_nmi(vmx->exit_intr_info)) {
		kvm_before_interrupt(&vmx->vcpu);
		asm("int $2");
		kvm_after_interrupt(&vmx->vcpu);
		@@ -6535,6 +6528,9 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
		vmx->idt_vectoring_info = 0;

		vmx->exit_reason = vmx->fail ? 0xdead : vmcs_read32(VM_EXIT_REASON);
		if ((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY)
		kvm_machine_check();

		if (vmx->fail \|\| (vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
		return;

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