From c70934e0ab2d2c4bb16bf70c3e3db8c064a1761b Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 28 Jul 2023 18:35:22 -0700 Subject: [PATCH] KVM: x86: Reject memslot MOVE operations if KVMGT is attached 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 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 Tested-by: Yongwei Ma Link: https://lore.kernel.org/r/20230729013535.1070024-17-seanjc@google.com Signed-off-by: Sean Christopherson Signed-off-by: Paolo Bonzini --- 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 772be81f97cc..cfd0b8092d06 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 36f0ba21661d..161e97e6caa9 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -12632,6 +12632,13 @@ 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; -- 2.11.0