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KVM: x86: acknowledgment mechanism for async pf page ready notifications

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If two page ready notifications happen back to back the second one is not
delivered and the only mechanism we currently have is
kvm_check_async_pf_completion() check in vcpu_run() loop. The check will
only be performed with the next vmexit when it happens and in some cases
it may take a while. With interrupt based page ready notification delivery
the situation is even worse: unlike exceptions, interrupts are not handled
immediately so we must check if the slot is empty. This is slow and
unnecessary. Introduce dedicated MSR_KVM_ASYNC_PF_ACK MSR to communicate
the fact that the slot is free and host should check its notification
queue. Mandate using it for interrupt based 'page ready' APF event
delivery.

As kvm_check_async_pf_completion() is going away from vcpu_run() we need
a way to communicate the fact that vcpu->async_pf.done queue has
transitioned from empty to non-empty state. Introduce
kvm_arch_async_page_present_queued() and KVM_REQ_APF_READY to do the job.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20200525144125.143875-7-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Vitaly Kuznetsov
2020-05-25 16:41:21 +02:00
committed by Paolo Bonzini
parent 2635b5c4a0
commit 557a961abb
6 changed files with 52 additions and 5 deletions
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3
arch/x86/include/asm/kvm_host.h
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@@ -86,6 +86,7 @@
#define KVM_REQ_TLB_FLUSH_CURRENT KVM_ARCH_REQ(26)
#define KVM_REQ_HV_TLB_FLUSH \
KVM_ARCH_REQ_FLAGS(27, KVM_REQUEST_NO_WAKEUP)
#define KVM_REQ_APF_READY KVM_ARCH_REQ(28)
#define CR0_RESERVED_BITS \
(~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \
@@ -775,6 +776,7 @@ struct kvm_vcpu_arch {
u32 host_apf_flags;
unsigned long nested_apf_token;
bool delivery_as_pf_vmexit;
bool pageready_pending;
} apf;
/* OSVW MSRs (AMD only) */
@@ -1662,6 +1664,7 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
struct kvm_async_pf *work);
void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu,
struct kvm_async_pf *work);
void kvm_arch_async_page_present_queued(struct kvm_vcpu *vcpu);
bool kvm_arch_can_dequeue_async_page_present(struct kvm_vcpu *vcpu);
extern bool kvm_find_async_pf_gfn(struct kvm_vcpu *vcpu, gfn_t gfn);