From: Sean Christopherson Date: Tue, 8 Aug 2023 23:20:57 +0000 (-0700) Subject: KVM: x86: Remove WARN sanity check on hypervisor timer vs. UNINITIALIZED vCPU X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=7b0151caf73a656b75b550e361648430233455a0;p=linux.git KVM: x86: Remove WARN sanity check on hypervisor timer vs. UNINITIALIZED vCPU Drop the WARN in KVM_RUN that asserts that KVM isn't using the hypervisor timer, a.k.a. the VMX preemption timer, for a vCPU that is in the UNINITIALIZIED activity state. The intent of the WARN is to sanity check that KVM won't drop a timer interrupt due to an unexpected transition to UNINITIALIZED, but unfortunately userspace can use various ioctl()s to force the unexpected state. Drop the sanity check instead of switching from the hypervisor timer to a software based timer, as the only reason to switch to a software timer when a vCPU is blocking is to ensure the timer interrupt wakes the vCPU, but said interrupt isn't a valid wake event for vCPUs in UNINITIALIZED state *and* the interrupt will be dropped in the end. Reported-by: Yikebaer Aizezi Closes: https://lore.kernel.org/all/CALcu4rbFrU4go8sBHk3FreP+qjgtZCGcYNpSiEXOLm==qFv7iQ@mail.gmail.com Reviewed-by: Paolo Bonzini Link: https://lore.kernel.org/r/20230808232057.2498287-1-seanjc@google.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 5ff77a70b3820..d293adc051459 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11084,12 +11084,17 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) r = -EINTR; goto out; } + /* - * It should be impossible for the hypervisor timer to be in - * use before KVM has ever run the vCPU. + * Don't bother switching APIC timer emulation from the + * hypervisor timer to the software timer, the only way for the + * APIC timer to be active is if userspace stuffed vCPU state, + * i.e. put the vCPU into a nonsensical state. Only an INIT + * will transition the vCPU out of UNINITIALIZED (without more + * state stuffing from userspace), which will reset the local + * APIC and thus cancel the timer or drop the IRQ (if the timer + * already expired). */ - WARN_ON_ONCE(kvm_lapic_hv_timer_in_use(vcpu)); - kvm_vcpu_srcu_read_unlock(vcpu); kvm_vcpu_block(vcpu); kvm_vcpu_srcu_read_lock(vcpu);