Messages in this thread | | | Subject | Re: [PATCH v4 02/15] KVM: async_pf: Add helper function to check completion queue | From | Gavin Shan <> | Date | Thu, 13 Jan 2022 15:38:43 +0800 |
| |
Hi Eric,
On 11/10/21 11:37 PM, Eric Auger wrote: > On 8/15/21 2:59 AM, Gavin Shan wrote: >> This adds inline helper kvm_check_async_pf_completion_queue() to >> check if there are pending completion in the queue. The empty stub >> is also added on !CONFIG_KVM_ASYNC_PF so that the caller needn't >> consider if CONFIG_KVM_ASYNC_PF is enabled. >> >> All checks on the completion queue is done by the newly added inline >> function since list_empty() and list_empty_careful() are interchangeable. > why is it interchangeable? >
I think the commit log is misleading. list_empty_careful() is more strict than list_empty(). In this patch, we replace list_empty() with list_empty_careful(). I will correct the commit log in next respin like below:
All checks on the completion queue is done by the newly added inline function where list_empty_careful() instead of list_empty() is used.
>> >> Signed-off-by: Gavin Shan <gshan@redhat.com> >> --- >> arch/x86/kvm/x86.c | 2 +- >> include/linux/kvm_host.h | 10 ++++++++++ >> virt/kvm/async_pf.c | 10 +++++----- >> virt/kvm/kvm_main.c | 4 +--- >> 4 files changed, 17 insertions(+), 9 deletions(-) >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index e5d5c5ed7dd4..7f35d9324b99 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -11591,7 +11591,7 @@ static inline bool kvm_guest_apic_has_interrupt(struct kvm_vcpu *vcpu) >> >> static inline bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu) >> { >> - if (!list_empty_careful(&vcpu->async_pf.done)) >> + if (kvm_check_async_pf_completion_queue(vcpu)) >> return true; >> >> if (kvm_apic_has_events(vcpu)) >> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h >> index 85b61a456f1c..a5f990f6dc35 100644 >> --- a/include/linux/kvm_host.h >> +++ b/include/linux/kvm_host.h >> @@ -339,12 +339,22 @@ struct kvm_async_pf { >> bool notpresent_injected; >> }; >> >> +static inline bool kvm_check_async_pf_completion_queue(struct kvm_vcpu *vcpu) >> +{ >> + return !list_empty_careful(&vcpu->async_pf.done); >> +} >> + >> void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu); >> void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu); >> bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, >> unsigned long hva, struct kvm_arch_async_pf *arch); >> int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu); >> #else >> +static inline bool kvm_check_async_pf_completion_queue(struct kvm_vcpu *vcpu) >> +{ >> + return false; >> +} >> + >> static inline void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu) { } >> #endif >> >> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c >> index dd777688d14a..d145a61a046a 100644 >> --- a/virt/kvm/async_pf.c >> +++ b/virt/kvm/async_pf.c >> @@ -70,7 +70,7 @@ static void async_pf_execute(struct work_struct *work) >> kvm_arch_async_page_present(vcpu, apf); >> >> spin_lock(&vcpu->async_pf.lock); >> - first = list_empty(&vcpu->async_pf.done); >> + first = !kvm_check_async_pf_completion_queue(vcpu); >> list_add_tail(&apf->link, &vcpu->async_pf.done); >> apf->vcpu = NULL; >> spin_unlock(&vcpu->async_pf.lock); >> @@ -122,7 +122,7 @@ void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu) >> spin_lock(&vcpu->async_pf.lock); >> } >> >> - while (!list_empty(&vcpu->async_pf.done)) { >> + while (kvm_check_async_pf_completion_queue(vcpu)) { > this is replaced by a stronger check. Please can you explain why is it > equivalent?
Access to the completion queue is protected by spinlock. So the additional check in list_empty_careful() to verify the head's prev/next are modified on the fly shouldn't happen. It means they're same in our case.
>> struct kvm_async_pf *work = >> list_first_entry(&vcpu->async_pf.done, >> typeof(*work), link); >> @@ -138,7 +138,7 @@ void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu) >> { >> struct kvm_async_pf *work; >> >> - while (!list_empty_careful(&vcpu->async_pf.done) && >> + while (kvm_check_async_pf_completion_queue(vcpu) && >> kvm_arch_can_dequeue_async_page_present(vcpu)) { >> spin_lock(&vcpu->async_pf.lock); >> work = list_first_entry(&vcpu->async_pf.done, typeof(*work), >> @@ -205,7 +205,7 @@ int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu) >> struct kvm_async_pf *work; >> bool first; >> >> - if (!list_empty_careful(&vcpu->async_pf.done)) >> + if (kvm_check_async_pf_completion_queue(vcpu)) >> return 0; >> >> work = kmem_cache_zalloc(async_pf_cache, GFP_ATOMIC); >> @@ -216,7 +216,7 @@ int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu) >> INIT_LIST_HEAD(&work->queue); /* for list_del to work */ >> >> spin_lock(&vcpu->async_pf.lock); >> - first = list_empty(&vcpu->async_pf.done); >> + first = !kvm_check_async_pf_completion_queue(vcpu); >> list_add_tail(&work->link, &vcpu->async_pf.done); >> spin_unlock(&vcpu->async_pf.lock); >> >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >> index b50dbe269f4b..8795503651b1 100644 >> --- a/virt/kvm/kvm_main.c >> +++ b/virt/kvm/kvm_main.c >> @@ -3282,10 +3282,8 @@ static bool vcpu_dy_runnable(struct kvm_vcpu *vcpu) >> if (kvm_arch_dy_runnable(vcpu)) >> return true; >> >> -#ifdef CONFIG_KVM_ASYNC_PF >> - if (!list_empty_careful(&vcpu->async_pf.done)) >> + if (kvm_check_async_pf_completion_queue(vcpu)) >> return true; >> -#endif >> >> return false; >> } >>
Thanks, Gavin
| |