Messages in this thread |  | | | Date | Mon, 02 Nov 2009 14:56:46 +0200 | | From | Avi Kivity <> | | Subject | Re: [PATCH 06/11] Inject asynchronous page fault into a guest if page is swapped out. |
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On 11/01/2009 01:56 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. >
That loses us page cache accesses, which may be the majority of accesses in some workloads.
If we allow the guest to ignore a fault, and ensure that a second access to an apf page from the same vcpu doesn't trigger another apf, we can simply ignore the apf in a guest when we can't schedule.
Probably best done with an enable bit for kernel-mode apfs.
> Signed-off-by: Gleb Natapov<gleb@redhat.com> > --- > arch/x86/include/asm/kvm_host.h | 20 +++ > arch/x86/kvm/mmu.c | 243 ++++++++++++++++++++++++++++++++++++++- > arch/x86/kvm/mmutrace.h | 60 ++++++++++ > arch/x86/kvm/paging_tmpl.h | 16 +++- > arch/x86/kvm/x86.c | 22 +++- >
Much of the code is generic, please move it to virt/kvm.
> +static void async_pf_execute(struct slow_work *work) > +{ > + struct page *page[1]; >
No need to make it an array, just pass its address.
> + struct kvm_mmu_async_pf *apf = > + container_of(work, struct kvm_mmu_async_pf, work); > + wait_queue_head_t *q =&apf->vcpu->wq; > + > + might_sleep(); > + > + down_read(&apf->mm->mmap_sem); > + get_user_pages(current, apf->mm, apf->addr, 1, 1, 0, page, NULL); > + up_read(&apf->mm->mmap_sem); > + > + spin_lock(&apf->vcpu->arch.mmu_async_pf_lock); > + list_add_tail(&apf->link,&apf->vcpu->arch.mmu_async_pf_done); > + apf->page = page[0]; > + spin_unlock(&apf->vcpu->arch.mmu_async_pf_lock); > + > + trace_kvm_mmu_async_pf_executed(apf->addr, apf->page, apf->token, > + apf->gva); >
_completed, but maybe better placed in vcpu context.
> + > +static bool can_do_async_pf(struct kvm_vcpu *vcpu) > +{ > + struct kvm_segment kvm_seg; > + > + if (!vcpu->arch.pv_shm || > + !(vcpu->arch.pv_shm->features& KVM_PV_SHM_FEATURES_ASYNC_PF) || > + kvm_event_needs_reinjection(vcpu)) > + return false; > + > + kvm_get_segment(vcpu,&kvm_seg, VCPU_SREG_CS); > + > + /* is userspace code? TODO check VM86 mode */ > + return !!(kvm_seg.selector& 3); >
There's a ->get_cpl() which is slightly faster. Note vm86 is perfectly fine for async pf.
> +static int setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn) > +{ > + struct kvm_mmu_async_pf *work; > + > + /* setup slow work */ > + > + /* do alloc atomic since if we are going to sleep anyway we > + may as well sleep faulting in page */ > + work = kmem_cache_zalloc(mmu_async_pf_cache, GFP_ATOMIC); > + 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->token = (vcpu->arch.async_pf_id++<< 12) | vcpu->vcpu_id; >
The shift truncates async_pf_id.
-- error compiling committee.c: too many arguments to function
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