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Date: Mon, 11 May 2020 18:47:49 +0200
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: kvm@...r.kernel.org, x86@...nel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Andy Lutomirski <luto@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
Wanpeng Li <wanpengli@...cent.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Jim Mattson <jmattson@...gle.com>,
Vivek Goyal <vgoyal@...hat.com>, Gavin Shan <gshan@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
linux-kernel@...r.kernel.org
Subject: [PATCH 5/8] KVM: x86: acknowledgment mechanism for async pf page ready notifications
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 type 2 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@...hat.com>
---
Documentation/virt/kvm/msr.rst | 18 +++++++++++++++---
arch/s390/include/asm/kvm_host.h | 2 ++
arch/x86/include/asm/kvm_host.h | 3 +++
arch/x86/include/uapi/asm/kvm_para.h | 1 +
arch/x86/kvm/x86.c | 26 ++++++++++++++++++++++----
virt/kvm/async_pf.c | 10 ++++++++++
6 files changed, 53 insertions(+), 7 deletions(-)
diff --git a/Documentation/virt/kvm/msr.rst b/Documentation/virt/kvm/msr.rst
index f988a36f226a..3c7afbcd243f 100644
--- a/Documentation/virt/kvm/msr.rst
+++ b/Documentation/virt/kvm/msr.rst
@@ -230,9 +230,10 @@ data:
The content of these bytes is a token which was previously delivered as
type 1 event. The event indicates the page in now available. Guest is
supposed to write '0' to the location when it is done handling type 2
- event so the next one can be delivered. MSR_KVM_ASYNC_PF_INT MSR
- specifying the interrupt vector for type 2 APF delivery needs to be
- written to before enabling APF mechanism in MSR_KVM_ASYNC_PF_EN.
+ event so the next one can be delivered. It is also supposed to write
+ '1' to MSR_KVM_ASYNC_PF_ACK every time after clearing the location,
+ this forces KVM to re-scan its queue and deliver next pending
+ notification.
Note, previously, type 2 (page present) events were delivered via the
same #PF exception as type 1 (page not present) events but this is
@@ -352,3 +353,14 @@ data:
Interrupt vector for asynchnonous page ready notifications delivery.
The vector has to be set up before asynchronous page fault mechanism
is enabled in MSR_KVM_ASYNC_PF_EN.
+
+MSR_KVM_ASYNC_PF_ACK:
+ 0x4b564d07
+
+data:
+ Asynchronous page fault (APF) acknowledgment.
+
+ When the guest is done processing type 2 APF event and 'pageready_token'
+ field in 'struct kvm_vcpu_pv_apf_data' is cleared it is supposed to
+ write '1' to bit 0 of the MSR, this caused the host to re-scan its queue
+ and check if there are more notifications pending.
diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index d6bcd34f3ec3..c9c5b8b71175 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -982,6 +982,8 @@ void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
struct kvm_async_pf *work);
+static inline void kvm_arch_async_page_present_queued(struct kvm_vcpu *vcpu) {}
+
void kvm_arch_crypto_clear_masks(struct kvm *kvm);
void kvm_arch_crypto_set_masks(struct kvm *kvm, unsigned long *apm,
unsigned long *aqm, unsigned long *adm);
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4a72ba26a532..0eeeb98ed02a 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -83,6 +83,7 @@
#define KVM_REQ_GET_VMCS12_PAGES KVM_ARCH_REQ(24)
#define KVM_REQ_APICV_UPDATE \
KVM_ARCH_REQ_FLAGS(25, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_APF_READY KVM_ARCH_REQ(26)
#define CR0_RESERVED_BITS \
(~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \
@@ -771,6 +772,7 @@ struct kvm_vcpu_arch {
u32 host_apf_reason;
unsigned long nested_apf_token;
bool delivery_as_pf_vmexit;
+ bool pageready_pending;
} apf;
/* OSVW MSRs (AMD only) */
@@ -1643,6 +1645,7 @@ 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_inject_async_page_present(struct kvm_vcpu *vcpu);
extern bool kvm_find_async_pf_gfn(struct kvm_vcpu *vcpu, gfn_t gfn);
diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
index c55ffa2c40b6..941fdf4569a4 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -51,6 +51,7 @@
#define MSR_KVM_PV_EOI_EN 0x4b564d04
#define MSR_KVM_POLL_CONTROL 0x4b564d05
#define MSR_KVM_ASYNC_PF_INT 0x4b564d06
+#define MSR_KVM_ASYNC_PF_ACK 0x4b564d07
struct kvm_steal_time {
__u64 steal;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d1e9b072d279..d21adc23a99f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1243,7 +1243,7 @@ static const u32 emulated_msrs_all[] = {
HV_X64_MSR_TSC_EMULATION_STATUS,
MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
- MSR_KVM_PV_EOI_EN, MSR_KVM_ASYNC_PF_INT,
+ MSR_KVM_PV_EOI_EN, MSR_KVM_ASYNC_PF_INT, MSR_KVM_ASYNC_PF_ACK,
MSR_IA32_TSC_ADJUST,
MSR_IA32_TSCDEADLINE,
@@ -2912,6 +2912,12 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
if (kvm_pv_enable_async_pf_int(vcpu, data))
return 1;
break;
+ case MSR_KVM_ASYNC_PF_ACK:
+ if (data & 0x1) {
+ vcpu->arch.apf.pageready_pending = false;
+ kvm_check_async_pf_completion(vcpu);
+ }
+ break;
case MSR_KVM_STEAL_TIME:
if (unlikely(!sched_info_on()))
@@ -3191,6 +3197,9 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
case MSR_KVM_ASYNC_PF_INT:
msr_info->data = vcpu->arch.apf.msr_int_val;
break;
+ case MSR_KVM_ASYNC_PF_ACK:
+ msr_info->data = 0;
+ break;
case MSR_KVM_STEAL_TIME:
msr_info->data = vcpu->arch.st.msr_val;
break;
@@ -8336,6 +8345,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
kvm_hv_process_stimers(vcpu);
if (kvm_check_request(KVM_REQ_APICV_UPDATE, vcpu))
kvm_vcpu_update_apicv(vcpu);
+ if (kvm_check_request(KVM_REQ_APF_READY, vcpu))
+ kvm_check_async_pf_completion(vcpu);
}
if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
@@ -8610,8 +8621,6 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
break;
}
- kvm_check_async_pf_completion(vcpu);
-
if (signal_pending(current)) {
r = -EINTR;
vcpu->run->exit_reason = KVM_EXIT_INTR;
@@ -10489,13 +10498,22 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
trace_kvm_async_pf_ready(work->arch.token, work->cr2_or_gpa);
if (kvm_pv_async_pf_enabled(vcpu) &&
- !apf_put_user_ready(vcpu, work->arch.token))
+ !apf_put_user_ready(vcpu, work->arch.token)) {
+ vcpu->arch.apf.pageready_pending = true;
kvm_apic_set_irq(vcpu, &irq, NULL);
+ }
vcpu->arch.apf.halted = false;
vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
}
+void kvm_arch_async_page_present_queued(struct kvm_vcpu *vcpu)
+{
+ kvm_make_request(KVM_REQ_APF_READY, vcpu);
+ if (!vcpu->arch.apf.pageready_pending)
+ kvm_vcpu_kick(vcpu);
+}
+
bool kvm_arch_can_inject_async_page_present(struct kvm_vcpu *vcpu)
{
if (!kvm_pv_async_pf_enabled(vcpu))
diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 15e5b037f92d..746d95cf98ad 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -51,6 +51,7 @@ static void async_pf_execute(struct work_struct *work)
unsigned long addr = apf->addr;
gpa_t cr2_or_gpa = apf->cr2_or_gpa;
int locked = 1;
+ bool first;
might_sleep();
@@ -69,10 +70,14 @@ 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);
list_add_tail(&apf->link, &vcpu->async_pf.done);
apf->vcpu = NULL;
spin_unlock(&vcpu->async_pf.lock);
+ if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first)
+ kvm_arch_async_page_present_queued(vcpu);
+
/*
* apf may be freed by kvm_check_async_pf_completion() after
* this point
@@ -202,6 +207,7 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
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))
return 0;
@@ -214,9 +220,13 @@ 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);
list_add_tail(&work->link, &vcpu->async_pf.done);
spin_unlock(&vcpu->async_pf.lock);
+ if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first)
+ kvm_arch_async_page_present_queued(vcpu);
+
vcpu->async_pf.queued++;
return 0;
}
--
2.25.4
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