Re: [RFC][PATCH] Drop FOLL_GET in GUP when doing async_pf in kvm
From: chai wen
Date: Fri Oct 11 2013 - 06:09:31 EST
On 10/10/2013 11:15 PM, Gleb Natapov wrote:
> On Thu, Oct 10, 2013 at 09:20:15PM +0800, chai wen wrote:
>> Hi Gleb
>>
>> Thanks for you explanation about async_pf in kvm.
>> Page pinning is not mandatory in kvm async_pf processing and probably should
>> be dropped later.this patch drops the FOLL_GET flag when doing GUP in async_pf
>> and uses a bool (marking result of GUP) to replace the *page in kvm_async_pf
>> structure to simplify some following async_pf check/clear processing.
> Thanks, but the patch need to be on top of
> git://git.kernel.org/pub/scm/virt/kvm/kvm.git queue branch.
>
> Some more comment bellow.
>
>> Thanks.
>>
>> Suggested-by: gleb@xxxxxxxxxx
>> Signed-off-by: chai wen <chaiw.fnst@xxxxxxxxxxxxxx>
>> ---
>> arch/x86/kvm/x86.c | 5 ++---
>> include/linux/kvm_host.h | 2 +-
>> virt/kvm/async_pf.c | 16 ++++++----------
>> 3 files changed, 9 insertions(+), 14 deletions(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index e5ca72a..0ff7d02 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -7282,8 +7282,7 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
>> {
>> int r;
>>
>> - if ((vcpu->arch.mmu.direct_map != work->arch.direct_map) ||
>> - is_error_page(work->page))
>> + if ((vcpu->arch.mmu.direct_map != work->arch.direct_map))
>> return;
>>
>> r = kvm_mmu_reload(vcpu);
>> @@ -7393,7 +7392,7 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
>> struct x86_exception fault;
>>
>> trace_kvm_async_pf_ready(work->arch.token, work->gva);
>> - if (is_error_page(work->page))
>> + if (!work->got_page)
>> work->arch.token = ~0; /* broadcast wakeup */
>> else
>> kvm_del_async_pf_gfn(vcpu, work->arch.gfn);
>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>> index 0fbbc7a..232a7d0 100644
>> --- a/include/linux/kvm_host.h
>> +++ b/include/linux/kvm_host.h
>> @@ -189,7 +189,7 @@ struct kvm_async_pf {
>> gva_t gva;
>> unsigned long addr;
>> struct kvm_arch_async_pf arch;
>> - struct page *page;
>> + bool got_page;
> I would call it wakeup_all.
>
>> bool done;
>> };
>>
>> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
>> index 8a39dda..0cafdc7 100644
>> --- a/virt/kvm/async_pf.c
>> +++ b/virt/kvm/async_pf.c
>> @@ -56,7 +56,7 @@ void kvm_async_pf_vcpu_init(struct kvm_vcpu *vcpu)
>>
>> static void async_pf_execute(struct work_struct *work)
>> {
>> - struct page *page = NULL;
>> + long nrpages = 0;
>> struct kvm_async_pf *apf =
>> container_of(work, struct kvm_async_pf, work);
>> struct mm_struct *mm = apf->mm;
>> @@ -68,13 +68,13 @@ static void async_pf_execute(struct work_struct *work)
>>
>> use_mm(mm);
>> down_read(&mm->mmap_sem);
>> - get_user_pages(current, mm, addr, 1, 1, 0, &page, NULL);
>> + nrpages = get_user_pages(current, mm, addr, 1, 1, 0, NULL, NULL);
>> up_read(&mm->mmap_sem);
>> unuse_mm(mm);
>>
>> spin_lock(&vcpu->async_pf.lock);
>> list_add_tail(&apf->link, &vcpu->async_pf.done);
>> - apf->page = page;
>> + apf->got_page = (1==nrpages);
> Space before and after ==, but this is not needed at all. It does
> not matter if GUP failed or not here. We need to wake up guest process
> that is waiting on a page, so just set wakeup_all to false in kvm_setup_async_pf().
Hi Gleb
Thanks for you reply.
It does not matter if GUP failed or not here. But in the original logic of
kvm_arch_async_page_ready and kvm_arch_async_page_present, there is
is_error_page
checking in them. I am not sure wheher this ‘logic’ should be dropped.
And in kvm_async_pf_wakeup_all we used a dummy bad page pointer to generate
boradcast wakeup before. if wakeup_all(bool) is marking the result of
gup should it be false in this function ?
thanks
>
>> apf->done = true;
>> spin_unlock(&vcpu->async_pf.lock);
>>
>> @@ -114,8 +114,6 @@ void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
>> list_entry(vcpu->async_pf.done.next,
>> typeof(*work), link);
>> list_del(&work->link);
>> - if (!is_error_page(work->page))
>> - kvm_release_page_clean(work->page);
>> kmem_cache_free(async_pf_cache, work);
>> }
>> spin_unlock(&vcpu->async_pf.lock);
>> @@ -135,14 +133,12 @@ void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
>> list_del(&work->link);
>> spin_unlock(&vcpu->async_pf.lock);
>>
>> - if (work->page)
>> + if (work->got_page)
>> kvm_arch_async_page_ready(vcpu, work);
>> kvm_arch_async_page_present(vcpu, work);
>>
>> list_del(&work->queue);
>> vcpu->async_pf.queued--;
>> - if (!is_error_page(work->page))
>> - kvm_release_page_clean(work->page);
>> kmem_cache_free(async_pf_cache, work);
>> }
>> }
>> @@ -165,7 +161,7 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn,
>> if (!work)
>> return 0;
>>
>> - work->page = NULL;
>> + work->got_page = false;
> Sp here do:
> work->wakeup_all = false;
>
>> work->done = false;
>> work->vcpu = vcpu;
>> work->gva = gva;
>> @@ -206,7 +202,7 @@ int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu)
>> if (!work)
>> return -ENOMEM;
>>
>> - work->page = KVM_ERR_PTR_BAD_PAGE;
>> + work->got_page = false;
> And here:
> work->wakeup_all = true;
>> INIT_LIST_HEAD(&work->queue); /* for list_del to work */
>>
>> spin_lock(&vcpu->async_pf.lock);
>> --
>> 1.7.1
> --
> Gleb.
> --
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--
Regards
chai wen
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