[Bug 209253] Loss of connectivity on guest after important host <-> guest traffic

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=209253

--- Comment #5 from Ian Pilcher (arequipeno@gmail.com) ---
Based on my git bisect, it looks like this commit is triggering the WARNING.

commit c49fa6397b6d29ce10c0ae5b2528bb004a14691f
Author: Alex Williamson <alex.williamson@redhat.com>
Date:   Mon Aug 17 11:08:18 2020 -0600

    vfio-pci: Avoid recursive read-lock usage

    [ Upstream commit bc93b9ae0151ae5ad5b8504cdc598428ea99570b ]

    A down_read on memory_lock is held when performing read/write accesses
    to MMIO BAR space, including across the copy_to/from_user() callouts
    which may fault.  If the user buffer for these copies resides in an
    mmap of device MMIO space, the mmap fault handler will acquire a
    recursive read-lock on memory_lock.  Avoid this by reducing the lock
    granularity.  Sequential accesses requiring multiple ioread/iowrite
    cycles are expected to be rare, therefore typical accesses should not
    see additional overhead.

    VGA MMIO accesses are expected to be non-fatal regardless of the PCI
    memory enable bit to allow legacy probing, this behavior remains with
    a comment added.  ioeventfds are now included in memory access testing,
    with writes dropped while memory space is disabled.

    Fixes: abafbc551fdd ("vfio-pci: Invalidate mmaps and block MMIO access on
disabled memory")
    Reported-by: Zhiyi Guo <zhguo@redhat.com>
    Tested-by: Zhiyi Guo <zhguo@redhat.com>
    Reviewed-by: Cornelia Huck <cohuck@redhat.com>
    Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>

 drivers/vfio/pci/vfio_pci_private.h |   2 +
 drivers/vfio/pci/vfio_pci_rdwr.c    | 120 ++++++++++++++++++++++++++++--------
 2 files changed, 98 insertions(+), 24 deletions(-)

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bc93b9ae0151ae5ad5b8504cdc598428ea99570b

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