Re: [PATCH] KVM: x86: accept userspace interrupt only if no event is injected

From: stsp
Date: Fri Jul 16 2021 - 03:32:28 EST

15.07.2021 00:38, Paolo Bonzini пишет:
Once an exception has been injected, any side effects related to
the exception (such as setting CR2 or DR6) have been taked

"taken"? Probably a typo.

Therefore, once KVM sets the VM-entry interruption information
field or the AMD EVENTINJ field, the next VM-entry must deliver that

Pending interrupts are processed after injected exceptions, so
in theory it would not be a problem to use KVM_INTERRUPT when
an injected exception is present. However, DOSBox

dosemu2 to be precise.

is using
run->ready_for_interrupt_injection to detect interrupt windows
and then using KVM_SET_SREGS/KVM_SET_REGS to inject the
interrupt manually. For this to work, the interrupt window
must be delayed after the completion of the previous event

Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Stas Sergeev <stsp2@xxxxxxxxx>
Tested-by: Stas Sergeev <stsp2@xxxxxxxxx>
Fixes: 71cc849b7093 ("KVM: x86: Fix split-irqchip vs interrupt injection window request")
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
arch/x86/kvm/x86.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fe3aaf195292..7fbab29b3569 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4342,6 +4342,9 @@ static int kvm_vcpu_ioctl_set_lapic(struct kvm_vcpu *vcpu,
static int kvm_cpu_accept_dm_intr(struct kvm_vcpu *vcpu)
+ if (kvm_event_needs_reinjection(vcpu))
+ return false;

kvm_event_needs_reinjection() seems
to miss exception.pending check.
Don't we need it too?

Also perhaps a comment would be good
to have to avoid it from disappearing again,
as obviously kvm devs tend to overlook
the possibility of injecting interrupts by hands.