Messages in this thread | | | Date | Wed, 30 Aug 2023 23:04:21 +0800 | Subject | Re: [PATCH v4 16/29] KVM: x86: Reject memslot MOVE operations if KVMGT is attached | From | Like Xu <> |
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On 2023/7/29 09:35, Sean Christopherson wrote: > Disallow moving memslots if the VM has external page-track users, i.e. if > KVMGT is being used to expose a virtual GPU to the guest, as KVMGT doesn't > correctly handle moving memory regions. > > Note, this is potential ABI breakage! E.g. userspace could move regions > that aren't shadowed by KVMGT without harming the guest. However, the > only known user of KVMGT is QEMU, and QEMU doesn't move generic memory
This change breaks two kvm selftests:
- set_memory_region_test; - memslot_perf_test;
Please help confirm if the tests/doc needs to be updated, or if the assumption needs to be further clarified.
> regions. KVM's own support for moving memory regions was also broken for > multiple years (albeit for an edge case, but arguably moving RAM is > itself an edge case), e.g. see commit edd4fa37baa6 ("KVM: x86: Allocate > new rmap and large page tracking when moving memslot"). > > Reviewed-by: Yan Zhao <yan.y.zhao@intel.com> > Tested-by: Yongwei Ma <yongwei.ma@intel.com> > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > arch/x86/include/asm/kvm_page_track.h | 3 +++ > arch/x86/kvm/mmu/page_track.c | 5 +++++ > arch/x86/kvm/x86.c | 7 +++++++ > 3 files changed, 15 insertions(+) > > diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h > index 8c4d216e3b2b..f744682648e7 100644 > --- a/arch/x86/include/asm/kvm_page_track.h > +++ b/arch/x86/include/asm/kvm_page_track.h > @@ -75,4 +75,7 @@ kvm_page_track_unregister_notifier(struct kvm *kvm, > void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new, > int bytes); > void kvm_page_track_flush_slot(struct kvm *kvm, struct kvm_memory_slot *slot); > + > +bool kvm_page_track_has_external_user(struct kvm *kvm); > + > #endif > diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c > index 891e5cc52b45..e6de9638e560 100644 > --- a/arch/x86/kvm/mmu/page_track.c > +++ b/arch/x86/kvm/mmu/page_track.c > @@ -303,3 +303,8 @@ void kvm_page_track_flush_slot(struct kvm *kvm, struct kvm_memory_slot *slot) > n->track_flush_slot(kvm, slot, n); > srcu_read_unlock(&head->track_srcu, idx); > } > + > +bool kvm_page_track_has_external_user(struct kvm *kvm) > +{ > + return hlist_empty(&kvm->arch.track_notifier_head.track_notifier_list); > +} > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 059571d5abed..4394bb49051f 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -12606,6 +12606,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, > struct kvm_memory_slot *new, > enum kvm_mr_change change) > { > + /* > + * KVM doesn't support moving memslots when there are external page > + * trackers attached to the VM, i.e. if KVMGT is in use. > + */ > + if (change == KVM_MR_MOVE && kvm_page_track_has_external_user(kvm)) > + return -EINVAL; > + > if (change == KVM_MR_CREATE || change == KVM_MR_MOVE) { > if ((new->base_gfn + new->npages - 1) > kvm_mmu_max_gfn()) > return -EINVAL;
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