Re: [PATCH V3 2/3] kvm: don't register wildcard MMIO EVENTFD on two buses

From: Jason Wang
Date: Sun Aug 30 2015 - 23:12:19 EST

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In reply to: Jason Wang: "Re: [PATCH V3 2/3] kvm: don't register wildcard MMIO EVENTFD on two buses"
Next in thread: Michael S. Tsirkin: "Re: [PATCH V3 2/3] kvm: don't register wildcard MMIO EVENTFD on two buses"
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On 08/26/2015 01:10 PM, Jason Wang wrote:
> On 08/25/2015 07:51 PM, Michael S. Tsirkin wrote:
>> > On Tue, Aug 25, 2015 at 05:05:47PM +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 <gleb@xxxxxxxxxx>
>>>> >> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>>>> >> > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
>>>> >> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
>>>> >> > ---
>>>> >> > Changes from V2:
>>>> >> > - Tweak styles and comment suggested by Cornelia.
>>>> >> > 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 | 31 +++++++++----------------------
>>>> >> > virt/kvm/kvm_main.c | 16 ++++++++++++++--
>>>> >> > 2 files changed, 23 insertions(+), 24 deletions(-)
>>>> >> >
>>>> >> > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
>>>> >> > index 9ff4193..c3ffdc3 100644
>>>> >> > --- a/virt/kvm/eventfd.c
>>>> >> > +++ b/virt/kvm/eventfd.c
>>>> >> > @@ -762,13 +762,16 @@ 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_args(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;
>>>> >> > + /* When length is ignored, MMIO is put on a separate bus, for
>>>> >> > + * faster lookups.
>>>> >> > + */
>>>> >> > + return args->len ? KVM_MMIO_BUS : KVM_FAST_MMIO_BUS;
>>>> >> > }
>>>> >> >
>>>> >> > static int
>>>> >> > @@ -779,7 +782,7 @@ 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_args(args);
>>>> >> > /* must be natural-word sized, or 0 to ignore length */
>>>> >> > switch (args->len) {
>>>> >> > case 0:
>>>> >> > @@ -843,16 +846,6 @@ 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 +853,6 @@ 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 +871,7 @@ 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_args(args);
>>>> >> > eventfd = eventfd_ctx_fdget(args->fd);
>>>> >> > if (IS_ERR(eventfd))
>>>> >> > return PTR_ERR(eventfd);
>>>> >> > @@ -901,10 +892,6 @@ 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;
>>>> >> > +}
>>>> >> > +
>> > Thinking more about this, invoking the 0-length write after
>> > the != 0 length one would be better: it would mean we only
>> > handle the userspace MMIO like this.
> Right.
>

Using current unittest. This patch is about 2.9% slower than before, and
invoking 0-length write after is still 1.1% slower (mmio-datamatch-eventfd).

/patch/result/-+%/
/base/2957/0/
/V3/3043/+2.9%/
/V3+invoking != 0 length first/2990/+1.1%/

So looks like the best method is not searching KVM_FAST_MMIO_BUS during
KVM_MMIO_BUS. Instead, let userspace to register both datamatch and
wildcard in this case. Does this sound good to you?
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Next message: Stephen Rothwell: "linux-next: manual merge of the trivial tree with the drm tree"
Previous message: Pratyush Anand: "Re: [RFC] watchdog: Add watchdog device control through sysfs attributes"
In reply to: Jason Wang: "Re: [PATCH V3 2/3] kvm: don't register wildcard MMIO EVENTFD on two buses"
Next in thread: Michael S. Tsirkin: "Re: [PATCH V3 2/3] kvm: don't register wildcard MMIO EVENTFD on two buses"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]