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KVM: VMX: Re-enter guest in fastpath for "spurious" preemption timer exits

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Re-enter the guest in the fast path if VMX preeemption timer VM-Exit was
"spurious", i.e. if KVM "soft disabled" the timer by writing -1u and by
some miracle the timer expired before any other VM-Exit occurred.  This is
just an intermediate step to cleaning up the preemption timer handling,
optimizing these types of spurious VM-Exits is not interesting as they are
extremely rare/infrequent.

Link: https://lore.kernel.org/r/20240110012705.506918-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2024-01-09 17:27:01 -08:00
parent 9c9025ea00
commit e6b5d16bbd
1 changed files with 9 additions and 2 deletions
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11
arch/x86/kvm/vmx/vmx.c
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@ -5992,8 +5992,15 @@ static fastpath_t handle_fastpath_preemption_timer(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
if (!vmx->req_immediate_exit &&
!unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled)) {
/*
* In the *extremely* unlikely scenario that this is a spurious VM-Exit
* due to the timer expiring while it was "soft" disabled, just eat the
* exit and re-enter the guest.
*/
if (unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled))
return EXIT_FASTPATH_REENTER_GUEST;
if (!vmx->req_immediate_exit) {
kvm_lapic_expired_hv_timer(vcpu);
return EXIT_FASTPATH_REENTER_GUEST;
}