[PATCH 4.19 154/190] KVM: VMX: Fix handling of #MC that occurs during VM-Entry

Greg Kroah-Hartman
2019-09-13T13:18:45Z

[ Upstream commit beb8d93b3e423043e079ef3dda19dad7b28467a8 ]

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: b060ca3b2e9e7 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/kvm/vmx.c | 20 ++++++++------------
1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index e4bba840a0708..82253d31842a2 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -10438,28 +10438,21 @@ 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);
@@ -10980,6 +10973,9 @@ static void __noclone 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;

--
2.20.1