From: Sean Christopherson seanjc@google.com

commit 98c25ead5eda5e9d41abe57839ad3e8caf19500c upstream.

Handle the switch to/from the hypervisor/software timer when a vCPU is blocking in common x86 instead of in VMX. Even though VMX is the only user of a hypervisor timer, the logic and all functions involved are generic x86 (unless future CPUs do something completely different and implement a hypervisor timer that runs regardless of mode).

Handling the switch in common x86 will allow for the elimination of the pre/post_blocks hooks, and also lets KVM switch back to the hypervisor timer if and only if it was in use (without additional params). Add a comment explaining why the switch cannot be deferred to kvm_sched_out() or kvm_vcpu_block().

Signed-off-by: Sean Christopherson seanjc@google.com Reviewed-by: Maxim Levitsky mlevitsk@redhat.com Message-Id: 20211208015236.1616697-8-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com [ta: Fix conflicts in vmx_pre_block and vmx_post_block as per Paolo's suggestion. Add Reported-by and Link tags.] Reported-by: syzbot+b6a74be92b5063a0f1ff@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?id=489beb3d76ef14cc6cd18125782dc6f86051a60... Tested-by: Tudor Ambarus tudor.ambarus@linaro.org Signed-off-by: Tudor Ambarus tudor.ambarus@linaro.org --- arch/x86/kvm/vmx/vmx.c | 6 ------ arch/x86/kvm/x86.c | 21 +++++++++++++++++++++ 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 9ce45554d637..c95c3675e8d5 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -7597,17 +7597,11 @@ static int vmx_pre_block(struct kvm_vcpu *vcpu) if (pi_pre_block(vcpu)) return 1;

- if (kvm_lapic_hv_timer_in_use(vcpu)) - kvm_lapic_switch_to_sw_timer(vcpu); - return 0; }

static void vmx_post_block(struct kvm_vcpu *vcpu) { - if (kvm_x86_ops.set_hv_timer) - kvm_lapic_switch_to_hv_timer(vcpu); - pi_post_block(vcpu); }

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 0622256cd768..5cb4af42ba64 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -10043,12 +10043,28 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)

static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu) { + bool hv_timer; + if (!kvm_arch_vcpu_runnable(vcpu) && (!kvm_x86_ops.pre_block || static_call(kvm_x86_pre_block)(vcpu) == 0)) { + /* + * Switch to the software timer before halt-polling/blocking as + * the guest's timer may be a break event for the vCPU, and the + * hypervisor timer runs only when the CPU is in guest mode. + * Switch before halt-polling so that KVM recognizes an expired + * timer before blocking. + */ + hv_timer = kvm_lapic_hv_timer_in_use(vcpu); + if (hv_timer) + kvm_lapic_switch_to_sw_timer(vcpu); + srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx); kvm_vcpu_block(vcpu); vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);

+ if (hv_timer) + kvm_lapic_switch_to_hv_timer(vcpu); + if (kvm_x86_ops.post_block) static_call(kvm_x86_post_block)(vcpu);

@@ -10287,6 +10303,11 @@ 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. + */ + WARN_ON_ONCE(kvm_lapic_hv_timer_in_use(vcpu)); kvm_vcpu_block(vcpu); if (kvm_apic_accept_events(vcpu) < 0) { r = 0;