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@xxxxxxxxxx>
---
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
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