| Message ID | 20230602161921.208564-11-amoorthy@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Improve scalability of KVM + userfaultfd live migration via annotated memory faults. | expand |
On Fri, Jun 02, 2023, Anish Moorthy wrote: > When the memslot flag is enabled, fail guest memory accesses for which > fast-gup fails (ie, where resolving the page fault would require putting > the faulting thread to sleep). > > Suggested-by: James Houghton <jthoughton@google.com> > Signed-off-by: Anish Moorthy <amoorthy@google.com> > --- > Documentation/virt/kvm/api.rst | 2 +- > arch/x86/kvm/mmu/mmu.c | 17 ++++++++++++----- > arch/x86/kvm/x86.c | 1 + > 3 files changed, 14 insertions(+), 6 deletions(-) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index 9daadbe2c7ed..aa7b4024fd41 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -7783,7 +7783,7 @@ bugs and reported to the maintainers so that annotations can be added. > 7.35 KVM_CAP_NOWAIT_ON_FAULT > ---------------------------- > > -:Architectures: None > +:Architectures: x86 > :Returns: -EINVAL. > > The presence of this capability indicates that userspace may pass the > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index cb71aae9aaec..288008a64e5c 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -4299,7 +4299,9 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work) > kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true, NULL); > } > > -static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) > +static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, > + struct kvm_page_fault *fault, > + bool nowait) More booleans!? Just say no! And in this case, there's no reason to pass in a flag, just handle this entirely in __kvm_faultin_pfn(). diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 7b6eab6f84e8..ebf21f1f43ce 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4302,6 +4302,7 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work) static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) { struct kvm_memory_slot *slot = fault->slot; + bool nowait = kvm_is_slot_nowait_on_fault(slot); bool async; /* @@ -4332,9 +4333,12 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault } async = false; - fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async, - fault->write, &fault->map_writable, - &fault->hva); + + fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, + nowait, false, + nowait ? NULL : &async, + fault->write, &fault->map_writable, &fault->hva); + if (!async) return RET_PF_CONTINUE; /* *pfn has correct page already */ On a related topic, I would *love* for someone to overhaul gfn_to_pfn() to replace the "booleans for everything" approach and instead have KVM pass FOLL_* flags internally. Rough sketch here: https://lkml.kernel.org/r/ZGvUsf7lMkrNDHuE%40google.com
On Wed, Jun 14, 2023 at 1:25 PM Sean Christopherson <seanjc@google.com> wrote: > > -static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) > > +static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, > > + struct kvm_page_fault *fault, > > + bool nowait) > > More booleans!? Just say no! And in this case, there's no reason to pass in a > flag, just handle this entirely in __kvm_faultin_pfn(). Ah, thanks: that extra parameter is a holdover from forever ago where "nowait" was a special thing that was read by handle_error_pfn(). Done.
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 9daadbe2c7ed..aa7b4024fd41 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -7783,7 +7783,7 @@ bugs and reported to the maintainers so that annotations can be added. 7.35 KVM_CAP_NOWAIT_ON_FAULT ---------------------------- -:Architectures: None +:Architectures: x86 :Returns: -EINVAL. The presence of this capability indicates that userspace may pass the diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index cb71aae9aaec..288008a64e5c 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4299,7 +4299,9 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work) kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true, NULL); } -static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) +static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, + struct kvm_page_fault *fault, + bool nowait) { struct kvm_memory_slot *slot = fault->slot; bool async; @@ -4332,9 +4334,12 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault } async = false; - fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async, - fault->write, &fault->map_writable, - &fault->hva); + + fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, + nowait, false, + nowait ? NULL : &async, + fault->write, &fault->map_writable, &fault->hva); + if (!async) return RET_PF_CONTINUE; /* *pfn has correct page already */ @@ -4368,7 +4373,9 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault, fault->mmu_seq = vcpu->kvm->mmu_invalidate_seq; smp_rmb(); - ret = __kvm_faultin_pfn(vcpu, fault); + ret = __kvm_faultin_pfn(vcpu, fault, + likely(fault->slot) + && kvm_slot_nowait_on_fault(fault->slot)); if (ret != RET_PF_CONTINUE) return ret; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index d15bacb3f634..4fbe9c811cc7 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4498,6 +4498,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_VM_DISABLE_NX_HUGE_PAGES: case KVM_CAP_IRQFD_RESAMPLE: case KVM_CAP_MEMORY_FAULT_INFO: + case KVM_CAP_NOWAIT_ON_FAULT: r = 1; break; case KVM_CAP_EXIT_HYPERCALL:
When the memslot flag is enabled, fail guest memory accesses for which fast-gup fails (ie, where resolving the page fault would require putting the faulting thread to sleep). Suggested-by: James Houghton <jthoughton@google.com> Signed-off-by: Anish Moorthy <amoorthy@google.com> --- Documentation/virt/kvm/api.rst | 2 +- arch/x86/kvm/mmu/mmu.c | 17 ++++++++++++----- arch/x86/kvm/x86.c | 1 + 3 files changed, 14 insertions(+), 6 deletions(-)