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Date: Mon, 10 Jun 2013 20:11:11 +0300
From: Gleb Natapov <gleb@...hat.com>
To: Dominik Dingel <dingel@...ux.vnet.ibm.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
kvm@...r.kernel.org, linux-s390@...r.kernel.org,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] PF: Additional flag for direct page fault inject
On Mon, Jun 10, 2013 at 02:03:47PM +0200, Dominik Dingel wrote:
> On some architectures, as on s390x we may want to be able to directly inject
> notifications to the guest in case of a swapped in page. Also on s390x
> there is no need to go from gfn to hva as by calling gmap_fault we already
> have the needed address.
>
> Due to a possible race, we now always have to insert the page to the queue.
> So if we are not able to schedule the async page, we have to remove it from
> the list again. As this is only when we also have to page in synchronously,
> the overhead is not really important.
>
> Signed-off-by: Dominik Dingel <dingel@...ux.vnet.ibm.com>
> ---
> arch/x86/kvm/mmu.c | 2 +-
> include/linux/kvm_host.h | 3 ++-
> virt/kvm/async_pf.c | 33 +++++++++++++++++++++++++++------
> 3 files changed, 30 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 956ca35..02a49a9 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3223,7 +3223,7 @@ static int kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn)
> arch.direct_map = vcpu->arch.mmu.direct_map;
> arch.cr3 = vcpu->arch.mmu.get_cr3(vcpu);
>
> - return kvm_setup_async_pf(vcpu, gva, gfn, &arch);
> + return kvm_setup_async_pf(vcpu, gva, gfn, &arch, false);
> }
>
> static bool can_do_async_pf(struct kvm_vcpu *vcpu)
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 9bd29ef..a798deb 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -165,12 +165,13 @@ struct kvm_async_pf {
> struct kvm_arch_async_pf arch;
> struct page *page;
> bool done;
> + bool direct_inject;
This will be true or false for all apfs for a given arch, so it is
better to do it as compile time switch.
> };
>
> void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu);
> void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu);
> int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn,
> - struct kvm_arch_async_pf *arch);
> + struct kvm_arch_async_pf *arch, bool is_direct);
> int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
> #endif
>
> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
> index ea475cd..a4a6483 100644
> --- a/virt/kvm/async_pf.c
> +++ b/virt/kvm/async_pf.c
> @@ -73,9 +73,17 @@ static void async_pf_execute(struct work_struct *work)
> unuse_mm(mm);
>
> spin_lock(&vcpu->async_pf.lock);
> - list_add_tail(&apf->link, &vcpu->async_pf.done);
> apf->page = page;
> apf->done = true;
> + if (apf->direct_inject) {
> + kvm_arch_async_page_present(vcpu, apf);
> + list_del(&apf->queue);
> + vcpu->async_pf.queued--;
> + kvm_release_page_clean(apf->page);
> + kmem_cache_free(async_pf_cache, apf);
kvm_clear_async_pf_completion_queue() walks async_pf.queue without
holding vcpu->async_pf.lock and I do not think we can take it there
either since cancel_work_sync() will probably deadlock.
> + } else {
> + list_add_tail(&apf->link, &vcpu->async_pf.done);
> + }
> spin_unlock(&vcpu->async_pf.lock);
>
> /*
> @@ -145,7 +153,7 @@ void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
> }
>
> int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn,
> - struct kvm_arch_async_pf *arch)
> + struct kvm_arch_async_pf *arch, bool is_direct)
> {
> struct kvm_async_pf *work;
>
> @@ -165,13 +173,24 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn,
> work->page = NULL;
> work->done = false;
> work->vcpu = vcpu;
> - work->gva = gva;
> - work->addr = gfn_to_hva(vcpu->kvm, gfn);
> + if (gfn == -1) {
Just change kvm_setup_async_pf() to receive addr as a parameter and do
gfn_to_hva() in the caller if needed.
> + work->gva = -1;
> + work->addr = gva;
> + } else {
> + work->gva = gva;
> + work->addr = gfn_to_hva(vcpu->kvm, gfn);
> + }
> + work->direct_inject = is_direct;
> work->arch = *arch;
> work->mm = current->mm;
> atomic_inc(&work->mm->mm_count);
> kvm_get_kvm(work->vcpu->kvm);
>
> + spin_lock(&vcpu->async_pf.lock);
> + list_add_tail(&work->queue, &vcpu->async_pf.queue);
> + vcpu->async_pf.queued++;
> + spin_unlock(&vcpu->async_pf.lock);
> +
> /* this can't really happen otherwise gfn_to_pfn_async
> would succeed */
> if (unlikely(kvm_is_error_hva(work->addr)))
> @@ -181,11 +200,13 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn,
> if (!schedule_work(&work->work))
> goto retry_sync;
>
> - list_add_tail(&work->queue, &vcpu->async_pf.queue);
> - vcpu->async_pf.queued++;
> kvm_arch_async_page_not_present(vcpu, work);
> return 1;
> retry_sync:
> + spin_lock(&vcpu->async_pf.lock);
> + list_del(&work->queue);
> + vcpu->async_pf.queued--;
> + spin_unlock(&vcpu->async_pf.lock);
> kvm_put_kvm(work->vcpu->kvm);
> mmdrop(work->mm);
> kmem_cache_free(async_pf_cache, work);
> --
> 1.8.1.6
--
Gleb.
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