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SubjectRe: [PATCH] vfio/pci: when irq_bypass_register_producer() return fails, we need to clean it up and return -EINVAL. instead of return true.
> On Tue, 29 Sep 2020 14:54:35 -0600
> Alex Williamson <alex.williamson@redhat.com> wrote:
>
> > On Sun, 27 Sep 2020 20:11:08 +0800
> > guomin_chen@sina.com wrote:
> >
> > > From: guomin chen <guomin_chen@sina.com>
> > >
> > > Since eventfd "fds" is passed as a parameter by the upper-level
> > > application,when "fds" has multiple identical 'fd', it causes
> > > multiple different vfio_pci_irq_ctx->trigger and producer->token
> > > pointing to the same eventfd file. Although all but the first one
> > > can register successfully,all others fail to register.
> > >
> > > So when others producer released later, the list_del(&producer->node)
> > > will be called due to the different producer->token pointing to the
> > > same eventfd file, then triggering the BUG():
> > >
> > > vfio-pci 0000:db:00.0: irq bypass producer (token 0000000060c8cda5) registration fails: -16
> > > vfio-pci 0000:db:00.0: irq bypass producer (token 0000000060c8cda5) registration fails: -16
> > > vfio-pci 0000:db:00.0: irq bypass producer (token 0000000060c8cda5) registration fails: -16
> > > vfio-pci 0000:db:00.0: irq bypass producer (token 0000000060c8cda5) registration fails: -16
> > > vfio-pci 0000:db:00.0: irq bypass producer (token 0000000060c8cda5) registration fails: -16
> > > list_del corruption, ffff8f7fb8ba0828->next is LIST_POISON1 (dead000000000100)
> > > ------------[ cut here ]------------
> > > kernel BUG at lib/list_debug.c:47!
> > > invalid opcode: 0000 [#1] SMP NOPTI
> > > CPU: 29 PID: 3914 Comm: qemu-kvm Kdump: loaded Tainted: G E
> > > -------- - -4.18.0-193.6.3.el8.x86_64 #1
> > > Hardware name: Lenovo ThinkSystem SR650 -[7X06CTO1WW]-/-[7X06CTO1WW]-,
> > > BIOS -[IVE636Z-2.13]- 07/18/2019
> > > RIP: 0010:__list_del_entry_valid.cold.1+0x12/0x4c
> > > Code: ce ff 0f 0b 48 89 c1 4c 89 c6 48 c7 c7 40 85 4d 88 e8 8c bc
> > > ce ff 0f 0b 48 89 fe 48 89 c2 48 c7 c7 d0 85 4d 88 e8 78 bc
> > > ce ff <0f> 0b 48 c7 c7 80 86 4d 88 e8 6a bc ce ff 0f 0b 48
> > > 89 f2 48 89 fe
> > > RSP: 0018:ffffaa9d60197d20 EFLAGS: 00010246
> > > RAX: 000000000000004e RBX: ffff8f7fb8ba0828 RCX: 0000000000000000
> > > RDX: 0000000000000000 RSI: ffff8f7fbf4d6a08 RDI: ffff8f7fbf4d6a08
> > > RBP: 0000000000000000 R08: 000000000000084b R09: 000000000000005d
> > > R10: 0000000000000000 R11: ffffaa9d60197bd0 R12: ffff8f4fbe863000
> > > R13: 00000000000000c2 R14: 0000000000000000 R15: 0000000000000000
> > > FS: 00007f7cb97fa700(0000) GS:ffff8f7fbf4c0000(0000)
> > > knlGS:0000000000000000
> > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > CR2: 00007fcf31da4000 CR3: 0000005f6d404001 CR4: 00000000007626e0
> > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > PKRU: 55555554
> > > Call Trace:
> > > irq_bypass_unregister_producer+0x9b/0xf0 [irqbypass]
> > > vfio_msi_set_vector_signal+0x8c/0x290 [vfio_pci]
> > > ? load_fixmap_gdt+0x22/0x30
> > > vfio_msi_set_block+0x6e/0xd0 [vfio_pci]
> > > vfio_pci_ioctl+0x218/0xbe0 [vfio_pci]
> > > ? kvm_vcpu_ioctl+0xf2/0x5f0 [kvm]
> > > do_vfs_ioctl+0xa4/0x630
> > > ? syscall_trace_enter+0x1d3/0x2c0
> > > ksys_ioctl+0x60/0x90
> > > __x64_sys_ioctl+0x16/0x20
> > > do_syscall_64+0x5b/0x1a0
> > > entry_SYSCALL_64_after_hwframe+0x65/0xca
> > >
> > > Cc: Alex Williamson <alex.williamson@redhat.com>
> > > Cc: Cornelia Huck <cohuck@redhat.com>
> > > Cc: Jiang Yi <giangyi@amazon.com>
> > > Cc: Marc Zyngier <maz@kernel.org>
> > > Cc: Peter Xu <peterx@redhat.com>
> > > Cc: Eric Auger <eric.auger@redhat.com>
> > > Cc: kvm@vger.kernel.org
> > > Cc: linux-kernel@vger.kernel.org
> > > Signed-off-by: guomin chen <guomin_chen@sina.com>
> > > ---
> > > drivers/vfio/pci/vfio_pci_intrs.c | 15 +++++++++++++--
> > > 1 file changed, 13 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
> > > index 1d9fb25..dd3a495 100644
> > > --- a/drivers/vfio/pci/vfio_pci_intrs.c
> > > +++ b/drivers/vfio/pci/vfio_pci_intrs.c
> > > @@ -352,10 +352,21 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_device *vdev,
> > > vdev->ctx[vector].producer.token = trigger;
> > > vdev->ctx[vector].producer.irq = irq;
> > > ret = irq_bypass_register_producer(&vdev->ctx[vector].producer);
> > > - if (unlikely(ret))
> > > - dev_info(&pdev->dev,
> > > + if (unlikely(ret)) {
> > > + dev_err(&pdev->dev,
> > > "irq bypass producer (token %p) registration fails: %d\n",
> > > vdev->ctx[vector].producer.token, ret);
> > > +
> > > + kfree(vdev->ctx[vector].name);
> > > + eventfd_ctx_put(trigger);
> > > +
> > > + cmd = vfio_pci_memory_lock_and_enable(vdev);
> > > + free_irq(irq, trigger);
> > > + vfio_pci_memory_unlock_and_restore(vdev, cmd);
> > > +
> > > + vdev->ctx[vector].trigger = NULL;
> > > + return -EINVAL;
> > > + }
> > >
> > > vdev->ctx[vector].trigger = trigger;
> > >
> >
> > This is not the correct solution. Registering an IRQ bypass is an
> > accelerator, not a requirement. Failure should never cause the ioctl
> > to fail. The scenario you describe is a valid user configuration, the
> > issue is that the de-registration passes a bogus producer object that
> > was never successfully registered, causing a false match. Therefore I
> > believe the solution is to simply clear the token on registration
> > failure to prevent that bogus match. That should result in all the
> > additional producer objects with the same trigger harmlessly falling
> > out of the unregister function. Can you validate and post such a
> > patch? Thanks,
>
> BTW, vhost_vdpa_setup_vq_irq() has the same bug (Cc MST & Jason).
> Thanks,
>
> Alex
>
Well, thank you very much for you explanation of IRQ bypass.
I'll continue to analyze and validate it.
Thanks Alex.

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