Re: [PATCH v5 09/12] Retry fault before vmentry

Gleb Natapov
2010-08-24T09:34:52Z

On Tue, Aug 24, 2010 at 12:25:33PM +0300, Avi Kivity wrote:
> On 07/19/2010 06:30 PM, Gleb Natapov wrote:
> >When page is swapped in it is mapped into guest memory only after guest
> >tries to access it again and generate another fault. To save this fault
> >we can map it immediately since we know that guest is going to access
> >the page.
> >
> >
> >
> >-static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa,
> >- u32 error_code)
> >+static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, u32 error_code,
> >+ bool sync)
>
> 'sync' means something else in the shadow mmu. Please rename to
> something longer, maybe 'apf_completion'.
>
> Alternatively, split to two functions, a base function that doesn't
> do apf and a wrapper that handles apf.
>
Will rename to something else.

> >@@ -505,6 +506,37 @@ out_unlock:
> > return 0;
> > }
> >
> >+static int FNAME(page_fault_other_cr3)(struct kvm_vcpu *vcpu, gpa_t cr3,
> >+ gva_t addr, u32 error_code)
> >+{
> >+ int r = 0;
> >+ gpa_t curr_cr3 = vcpu->arch.cr3;
> >+
> >+ if (curr_cr3 != cr3) {
> >+ /*
> >+ * We do page fault on behalf of a process that is sleeping
> >+ * because of async PF. PV guest takes reference to mm that cr3
> >+ * belongs too, so it has to be valid here.
> >+ */
> >+ kvm_set_cr3(vcpu, cr3);
> >+ if (kvm_mmu_reload(vcpu))
> >+ goto switch_cr3;
> >+ }
>
> With nested virtualization, we need to switch cr0, cr4, and efer as well...
>
On SVM or VMX or both?

> >+
> >+ r = FNAME(page_fault)(vcpu, addr, error_code, true);
> >+
> >+ if (kvm_check_request(KVM_REQ_MMU_SYNC, vcpu))
> >+ kvm_mmu_sync_roots(vcpu);
>
> Why is this needed?
>
http://www.mail-archive.com/kvm@vger.kernel.org/msg37827.html

KVM_REQ_MMU_SYNC request generated here must be processed before
switching to a different cr3 (otherwise vcpu_enter_guest will process it
with the wrong cr3 in place).

> >+
> >+switch_cr3:
> >+ if (curr_cr3 != vcpu->arch.cr3) {
> >+ kvm_set_cr3(vcpu, curr_cr3);
> >+ kvm_mmu_reload(vcpu);
> >+ }
> >+
> >+ return r;
> >+}
>
> This has the nasty effect of flushing the TLB on AMD.
>
What is more expansive reenter the guest and handle one more fault, or
flash TLB here?

> >+
> > static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva)
> > {
> > struct kvm_shadow_walk_iterator iterator;
> >diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >index 2603cc4..5482db0 100644
> >--- a/arch/x86/kvm/x86.c
> >+++ b/arch/x86/kvm/x86.c
> >@@ -5743,6 +5743,15 @@ void kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
> > }
> > EXPORT_SYMBOL_GPL(kvm_set_rflags);
> >
> >+void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu,
> >+ struct kvm_async_pf *work)
> >+{
> >+ if (!vcpu->arch.mmu.page_fault_other_cr3 || is_error_page(work->page))
> >+ return;
> >+ vcpu->arch.mmu.page_fault_other_cr3(vcpu, work->arch.cr3, work->gva,
> >+ work->arch.error_code);
> >+}
> >+
> > static int apf_put_user(struct kvm_vcpu *vcpu, u32 val)
> > {
> > if (unlikely(vcpu->arch.apf_memslot_ver !=
> >diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> >index f56e8ac..de1d5b6 100644
> >--- a/virt/kvm/kvm_main.c
> >+++ b/virt/kvm/kvm_main.c
> >@@ -1348,6 +1348,7 @@ void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
> > spin_lock(&vcpu->async_pf_lock);
> > list_del(&work->link);
> > spin_unlock(&vcpu->async_pf_lock);
> >+ kvm_arch_async_page_ready(vcpu, work);
> > put_page(work->page);
> > async_pf_work_free(work);
> > list_del(&work->queue);
> >@@ -1366,6 +1367,7 @@ void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
> > list_del(&work->queue);
> > vcpu->async_pf_queued--;
> >
> >+ kvm_arch_async_page_ready(vcpu, work);
> > kvm_arch_inject_async_page_present(vcpu, work);
> >
> > put_page(work->page);
>
>
> --
> error compiling committee.c: too many arguments to function

--
Gleb.