On Mon, Nov 02, 2009 at 02:56:46PM +0200, Avi Kivity wrote:
> 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.
>
This is addressed later in the patch series.
> 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@xxxxxxxxxx>
> >---
> > 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.
>
OK, Will move generic part to virt.
> >+static void async_pf_execute(struct slow_work *work)
> >+{
> >+ struct page *page[1];
>
> No need to make it an array, just pass its address.
>
OK
> >+ 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.
>
OK. But the code is removed by following patches anyway.
> >+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.
>
Will fix.
--
Gleb.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
