Re: [PATCH v5 08/12] Inject asynchronous page fault into a guestif page is swapped out.
From: Avi Kivity
Date: Mon Aug 23 2010 - 12:18:17 EST
On 07/19/2010 06:30 PM, Gleb Natapov wrote:
If guest access swapped out memory do not swap it in from vcpu thread
context. Setup slow work to do swapping and send async page fault to
a guest.
Allow async page fault injection only when guest is in user mode since
otherwise guest may be in non-sleepable context and will not be able to
reschedule.
struct kvm_arch {
@@ -444,6 +446,8 @@ struct kvm_vcpu_stat {
u32 hypercalls;
u32 irq_injections;
u32 nmi_injections;
+ u32 apf_not_present;
+ u32 apf_present;
};
Please don't add more stats, instead add tracepoints which can be
converted to stats by userspace.
Would be good to have both guest and host tracepoints.
@@ -2345,6 +2346,21 @@ static int nonpaging_page_fault(struct kvm_vcpu *vcpu, gva_t gva,
error_code& PFERR_WRITE_MASK, gfn);
}
+int kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn)
+{
+ struct kvm_arch_async_pf arch;
+ arch.token = (vcpu->arch.async_pf_id++<< 12) | vcpu->vcpu_id;
+ return kvm_setup_async_pf(vcpu, gva, gfn,&arch);
+}
Ok. so token is globally unique. We're limited to 4096 vcpus, I guess
that's fine. Wraparound at 1M faults/vcpu, what's the impact? failure
if we have 1M faulting processes on one vcpu?
I guess that's fine too.
+
+static bool can_do_async_pf(struct kvm_vcpu *vcpu)
+{
+ if (!vcpu->arch.apf_data || kvm_event_needs_reinjection(vcpu))
+ return false;
+
+ return !!kvm_x86_ops->get_cpl(vcpu);
!! !needed, bool autoconverts. But > 0 is more readable.
+}
+
static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa,
u32 error_code)
{
@@ -2353,6 +2369,7 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa,
int level;
gfn_t gfn = gpa>> PAGE_SHIFT;
unsigned long mmu_seq;
+ bool async;
ASSERT(vcpu);
ASSERT(VALID_PAGE(vcpu->arch.mmu.root_hpa));
@@ -2367,7 +2384,23 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa,
mmu_seq = vcpu->kvm->mmu_notifier_seq;
smp_rmb();
- pfn = gfn_to_pfn(vcpu->kvm, gfn);
+
+ if (can_do_async_pf(vcpu)) {
+ pfn = gfn_to_pfn_async(vcpu->kvm, gfn,&async);
+ trace_kvm_try_async_get_page(async, pfn);
+ } else {
+do_sync:
+ async = false;
+ pfn = gfn_to_pfn(vcpu->kvm, gfn);
+ }
+
+ if (async) {
+ if (!kvm_arch_setup_async_pf(vcpu, gpa, gfn))
+ goto do_sync;
+ return 0;
+ }
+
This goto is pretty ugly. How about:
async = false;
if (can_do_async_pf(&async)) {
}
if (async && !setup())
async = false;
if (async)
...
or something.
@@ -459,7 +460,21 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
mmu_seq = vcpu->kvm->mmu_notifier_seq;
smp_rmb();
- pfn = gfn_to_pfn(vcpu->kvm, walker.gfn);
+
+ if (can_do_async_pf(vcpu)) {
+ pfn = gfn_to_pfn_async(vcpu->kvm, walker.gfn,&async);
+ trace_kvm_try_async_get_page(async, pfn);
+ } else {
+do_sync:
+ async = false;
+ pfn = gfn_to_pfn(vcpu->kvm, walker.gfn);
+ }
+
+ if (async) {
+ if (!kvm_arch_setup_async_pf(vcpu, addr, walker.gfn))
+ goto do_sync;
+ return 0;
+ }
This repetition is ugly too.
+static int apf_put_user(struct kvm_vcpu *vcpu, u32 val)
+{
+ if (unlikely(vcpu->arch.apf_memslot_ver !=
+ vcpu->kvm->memslot_version)) {
+ u64 gpa = vcpu->arch.apf_msr_val& ~0x3f;
+ unsigned long addr;
+ int offset = offset_in_page(gpa);
+
+ addr = gfn_to_hva(vcpu->kvm, gpa>> PAGE_SHIFT);
+ vcpu->arch.apf_data = (u32 __user *)(addr + offset);
+ if (kvm_is_error_hva(addr)) {
+ vcpu->arch.apf_data = NULL;
+ return -EFAULT;
+ }
+ }
+
+ return put_user(val, vcpu->arch.apf_data);
+}
This nice cache needs to be outside apf to reduce complexity for
reviewers and since it is useful for others.
Would be good to have memslot-cached kvm_put_guest() and kvm_get_guest().
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 292514c..f56e8ac 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -78,6 +78,11 @@ static atomic_t hardware_enable_failed;
struct kmem_cache *kvm_vcpu_cache;
EXPORT_SYMBOL_GPL(kvm_vcpu_cache);
+#ifdef CONFIG_KVM_ASYNC_PF
+#define ASYNC_PF_PER_VCPU 100
+static struct kmem_cache *async_pf_cache;
+#endif
All those #ifdefs can be eliminated with virt/kvm/apf.[ch].
+
static __read_mostly struct preempt_ops kvm_preempt_ops;
struct dentry *kvm_debugfs_dir;
@@ -186,6 +191,11 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
vcpu->kvm = kvm;
vcpu->vcpu_id = id;
init_waitqueue_head(&vcpu->wq);
+#ifdef CONFIG_KVM_ASYNC_PF
+ INIT_LIST_HEAD(&vcpu->async_pf_done);
+ INIT_LIST_HEAD(&vcpu->async_pf_queue);
+ spin_lock_init(&vcpu->async_pf_lock);
+#endif
kvm_apf_init() etc.
+ struct kvm_arch_async_pf *arch)
+{
+ struct kvm_async_pf *work;
+
+ if (vcpu->async_pf_queued>= ASYNC_PF_PER_VCPU)
+ return 0;
100 == too high. At 16 vcpus, this allows 1600 kernel threads to wait
for I/O.
Would have been best if we could ask for a page to be paged in
asynchronously.
+
+ /* setup slow work */
+
+ /* do alloc nowait since if we are going to sleep anyway we
+ may as well sleep faulting in page */
+ work = kmem_cache_zalloc(async_pf_cache, GFP_NOWAIT);
+ if (!work)
+ return 0;
+
+ atomic_set(&work->used, 1);
+ work->page = NULL;
+ work->vcpu = vcpu;
+ work->gva = gva;
+ work->addr = gfn_to_hva(vcpu->kvm, gfn);
+ work->arch = *arch;
+ work->mm = current->mm;
+ atomic_inc(&work->mm->mm_count);
+ kvm_get_kvm(work->vcpu->kvm);
+
+ /* this can't really happen otherwise gfn_to_pfn_async
+ would succeed */
+ if (unlikely(kvm_is_error_hva(work->addr)))
+ goto retry_sync;
+
+ slow_work_init(&work->work,&async_pf_ops);
+ if (slow_work_enqueue(&work->work) != 0)
+ goto retry_sync;
+
+ vcpu->async_pf_work = work;
+ list_add_tail(&work->queue,&vcpu->async_pf_queue);
+ vcpu->async_pf_queued++;
+ return 1;
+retry_sync:
+ kvm_put_kvm(work->vcpu->kvm);
+ mmdrop(work->mm);
+ kmem_cache_free(async_pf_cache, work);
+ return 0;
+}
+
+
--
error compiling committee.c: too many arguments to function
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