On Tue, Aug 25, 2015 at 03:47:14PM +0800, Jason Wang wrote: > We register wildcard mmio eventfd on two buses, one for KVM_MMIO_BUS > and another is KVM_FAST_MMIO_BUS. This leads to issue: > > - kvm_io_bus_destroy() knows nothing about the devices on two buses > points to a single dev. Which will lead double free [1] during exit. > - wildcard eventfd ignores data len, so it was registered as a > kvm_io_range with zero length. This will fail the binary search in > kvm_io_bus_get_first_dev() when we try to emulate through > KVM_MMIO_BUS. This will cause userspace io emulation request instead > of a eventfd notification (virtqueue kick will be trapped by qemu > instead of vhost in this case). > > Fixing this by don't register wildcard mmio eventfd on two > buses. Instead, only register it in KVM_FAST_MMIO_BUS. This fixes the > double free issue of kvm_io_bus_destroy(). For the arch/setups that > does not utilize KVM_FAST_MMIO_BUS, before searching KVM_MMIO_BUS, try > KVM_FAST_MMIO_BUS first to see it it has a match. > > [1] Panic caused by double free: > > CPU: 1 PID: 2894 Comm: qemu-system-x86 Not tainted 3.19.0-26-generic > #28-Ubuntu > Hardware name: LENOVO 2356BG6/2356BG6, BIOS G7ET96WW (2.56 ) 09/12/2013 > task: ffff88009ae0c4b0 ti: ffff88020e7f0000 task.ti: ffff88020e7f0000 > RIP: 0010:[<ffffffffc07e25d8>] [<ffffffffc07e25d8>] > ioeventfd_release+0x28/0x60 [kvm] > RSP: 0018:ffff88020e7f3bc8 EFLAGS: 00010292 > RAX: dead000000200200 RBX: ffff8801ec19c900 RCX: 000000018200016d > RDX: ffff8801ec19cf80 RSI: ffffea0008bf1d40 RDI: ffff8801ec19c900 > RBP: ffff88020e7f3bd8 R08: 000000002fc75a01 R09: 000000018200016d > R10: ffffffffc07df6ae R11: ffff88022fc75a98 R12: ffff88021e7cc000 > R13: ffff88021e7cca48 R14: ffff88021e7cca50 R15: ffff8801ec19c880 > FS: 00007fc1ee3e6700(0000) GS:ffff88023e240000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f8f389d8000 CR3: 000000023dc13000 CR4: 00000000001427e0 > Stack: > ffff88021e7cc000 0000000000000000 ffff88020e7f3be8 ffffffffc07e2622 > ffff88020e7f3c38 ffffffffc07df69a ffff880232524160 ffff88020e792d80 > 0000000000000000 ffff880219b78c00 0000000000000008 ffff8802321686a8 > Call Trace: > [<ffffffffc07e2622>] ioeventfd_destructor+0x12/0x20 [kvm] > [<ffffffffc07df69a>] kvm_put_kvm+0xca/0x210 [kvm] > [<ffffffffc07df818>] kvm_vcpu_release+0x18/0x20 [kvm] > [<ffffffff811f69f7>] __fput+0xe7/0x250 > [<ffffffff811f6bae>] ____fput+0xe/0x10 > [<ffffffff81093f04>] task_work_run+0xd4/0xf0 > [<ffffffff81079358>] do_exit+0x368/0xa50 > [<ffffffff81082c8f>] ? recalc_sigpending+0x1f/0x60 > [<ffffffff81079ad5>] do_group_exit+0x45/0xb0 > [<ffffffff81085c71>] get_signal+0x291/0x750 > [<ffffffff810144d8>] do_signal+0x28/0xab0 > [<ffffffff810f3a3b>] ? do_futex+0xdb/0x5d0 > [<ffffffff810b7028>] ? __wake_up_locked_key+0x18/0x20 > [<ffffffff810f3fa6>] ? SyS_futex+0x76/0x170 > [<ffffffff81014fc9>] do_notify_resume+0x69/0xb0 > [<ffffffff817cb9af>] int_signal+0x12/0x17 > Code: 5d c3 90 0f 1f 44 00 00 55 48 89 e5 53 48 89 fb 48 83 ec 08 48 8b 7f 20 > e8 06 d6 a5 c0 48 8b 43 08 48 8b 13 48 89 df 48 89 42 08 <48> 89 10 48 b8 00 > 01 10 00 00 > RIP [<ffffffffc07e25d8>] ioeventfd_release+0x28/0x60 [kvm] > RSP <ffff88020e7f3bc8> > > Cc: Gleb Natapov <g...@kernel.org> > Cc: Paolo Bonzini <pbonz...@redhat.com> > Cc: Michael S. Tsirkin <m...@redhat.com> > Signed-off-by: Jason Wang <jasow...@redhat.com>
I'm worried that this slows down the regular MMIO. Could you share performance #s please? You need a mix of len=0 and len=2 matches. One solution for the first issue is to create two ioeventfd objects instead. For the second issue, we could change bsearch compare function instead. Again, affects all devices to performance #s would be needed. > --- > Changes from v1: > - change ioeventfd_bus_from_flags() to return KVM_FAST_MMIO_BUS when > needed to save lots of unnecessary changes. > --- > virt/kvm/eventfd.c | 30 ++++++++---------------------- > virt/kvm/kvm_main.c | 16 ++++++++++++++-- > 2 files changed, 22 insertions(+), 24 deletions(-) > > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c > index 9ff4193..95f2901 100644 > --- a/virt/kvm/eventfd.c > +++ b/virt/kvm/eventfd.c > @@ -762,13 +762,15 @@ ioeventfd_check_collision(struct kvm *kvm, struct > _ioeventfd *p) > return false; > } > > -static enum kvm_bus ioeventfd_bus_from_flags(__u32 flags) > +static enum kvm_bus ioeventfd_bus_from_flags(struct kvm_ioeventfd *args) > { > - if (flags & KVM_IOEVENTFD_FLAG_PIO) > + if (args->flags & KVM_IOEVENTFD_FLAG_PIO) > return KVM_PIO_BUS; > - if (flags & KVM_IOEVENTFD_FLAG_VIRTIO_CCW_NOTIFY) > + if (args->flags & KVM_IOEVENTFD_FLAG_VIRTIO_CCW_NOTIFY) > return KVM_VIRTIO_CCW_NOTIFY_BUS; > - return KVM_MMIO_BUS; > + if (args->len) > + return KVM_MMIO_BUS; > + return KVM_FAST_MMIO_BUS; > } > > static int > @@ -779,7 +781,7 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct > kvm_ioeventfd *args) > struct eventfd_ctx *eventfd; > int ret; > > - bus_idx = ioeventfd_bus_from_flags(args->flags); > + bus_idx = ioeventfd_bus_from_flags(args); > /* must be natural-word sized, or 0 to ignore length */ > switch (args->len) { > case 0: > @@ -843,16 +845,6 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct > kvm_ioeventfd *args) > if (ret < 0) > goto unlock_fail; > > - /* When length is ignored, MMIO is also put on a separate bus, for > - * faster lookups. > - */ > - if (!args->len && !(args->flags & KVM_IOEVENTFD_FLAG_PIO)) { > - ret = kvm_io_bus_register_dev(kvm, KVM_FAST_MMIO_BUS, > - p->addr, 0, &p->dev); > - if (ret < 0) > - goto register_fail; > - } > - > kvm->buses[bus_idx]->ioeventfd_count++; > list_add_tail(&p->list, &kvm->ioeventfds); > > @@ -860,8 +852,6 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct > kvm_ioeventfd *args) > > return 0; > > -register_fail: > - kvm_io_bus_unregister_dev(kvm, bus_idx, &p->dev); > unlock_fail: > mutex_unlock(&kvm->slots_lock); > > @@ -880,7 +870,7 @@ kvm_deassign_ioeventfd(struct kvm *kvm, struct > kvm_ioeventfd *args) > struct eventfd_ctx *eventfd; > int ret = -ENOENT; > > - bus_idx = ioeventfd_bus_from_flags(args->flags); > + bus_idx = ioeventfd_bus_from_flags(args); > eventfd = eventfd_ctx_fdget(args->fd); > if (IS_ERR(eventfd)) > return PTR_ERR(eventfd); > @@ -901,10 +891,6 @@ kvm_deassign_ioeventfd(struct kvm *kvm, struct > kvm_ioeventfd *args) > continue; > > kvm_io_bus_unregister_dev(kvm, bus_idx, &p->dev); > - if (!p->length) { > - kvm_io_bus_unregister_dev(kvm, KVM_FAST_MMIO_BUS, > - &p->dev); > - } > kvm->buses[bus_idx]->ioeventfd_count--; > ioeventfd_release(p); > ret = 0; > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 0d79fe8..3e3b3bc 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -3152,8 +3152,8 @@ static int __kvm_io_bus_write(struct kvm_vcpu *vcpu, > struct kvm_io_bus *bus, > } > > /* kvm_io_bus_write - called under kvm->slots_lock */ > -int kvm_io_bus_write(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr, > - int len, const void *val) > +static int kvm_io_bus_write_idx(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, > + gpa_t addr, int len, const void *val) > { > struct kvm_io_bus *bus; > struct kvm_io_range range; > @@ -3169,6 +3169,18 @@ int kvm_io_bus_write(struct kvm_vcpu *vcpu, enum > kvm_bus bus_idx, gpa_t addr, > return r < 0 ? r : 0; > } > > +int kvm_io_bus_write(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr, > + int len, const void *val) > +{ > + int r = 0; > + > + if (bus_idx != KVM_MMIO_BUS || > + kvm_io_bus_write_idx(vcpu, KVM_FAST_MMIO_BUS, addr, 0, NULL) < 0) > + r = kvm_io_bus_write_idx(vcpu, bus_idx, addr, len, val); > + > + return r < 0 ? r : 0; > +} > + > /* kvm_io_bus_write_cookie - called under kvm->slots_lock */ > int kvm_io_bus_write_cookie(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, > gpa_t addr, int len, const void *val, long cookie) > -- > 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html