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Date: Tue, 25 Aug 2015 14:33:48 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: gleb@...nel.org, pbonzini@...hat.com, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, cornelia.huck@...ibm.com
Subject: Re: [PATCH V2 2/3] kvm: don't register wildcard MMIO EVENTFD on two
buses
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 <gleb@...nel.org>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Signed-off-by: Jason Wang <jasowang@...hat.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
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