Re: [PATCH v5 0/3] vfio/pci: Request resources and map BARs at enable time

[Alex Williamson <alex@shazbot.org>]

On Mon, 11 May 2026 07:58:22 -0700
Matt Evans <mattev@meta.com> wrote:

> Hi,
> 
> These patches fix a potential race for concurrent calls to
> vfio_pci_core_setup_barmap(), and a DMABUF missing check for resource
> before the export.  Discussion on a previous series (different,
> replaced by this one) is here:
> 
>  https://lore.kernel.org/kvm/20260415181423.1008458-1-mattev@meta.com
> 
> Responses in that thread indicated there wasn't a strong historical
> reason to require the mapping to be performed on-demand at BAR
> reference time.  It's much simpler to move this earlier, to
> vfio_pci_core_enable(), and that then avoids having to deal with
> concurrent requests later.
> 
> The first patch requests PCI resources and pci_iomap() of the BARs
> from vfio_pci_core_enable(), moving this out of
> vfio_pci_core_setup_barmap().
> 
> Some callers rely on vfio_pci_core_setup_barmap() for its ioremap()
> effect, and other callers use it for its resource-acquiring effect.
> The function turns into a cheap error check that both these actions
> have occurred; that maintains the same error behaviour as before the
> fix.
> 
> The second patch adds a call to vfio_pci_core_setup_barmap() to VFIO
> DMABUF export to check the resource is reserved; previously this was
> able to export an unrequested resource.  Although patch 1 at first
> appears to fix this by requesting resources at enable time, code using
> the BAR still needs to check the resource really was acquired.
> 
> (FWIW, Leon gave a R-B on v2 in
> https://lore.kernel.org/kvm/20260426111606.GC440345@unreal/ though
> this repost isn't 100% identical so I didn't propagate it.)
> 
> The third patch refactors vfio_pci_core_setup_barmap() plus the various
> vdev->barmap[] accesses into vfio_pci_core_get_iomap() which returns
> either a pointer to the mapping or an ERR_PTR() describing why it
> doesn't exist.  This is used by callers that need the mapping, but
> also by other callers to check that the resource/mapping step was
> successful.
> 
> Matt Evans (3):
>   vfio/pci: Set up BAR resources and maps in vfio_pci_core_enable()
>   vfio/pci: Check BAR resources before exporting a DMABUF
>   vfio/pci: Replace vfio_pci_core_setup_barmap() with
>     vfio_pci_core_get_iomap()
> 
>  drivers/vfio/pci/nvgrace-gpu/main.c | 20 +++++++-----
>  drivers/vfio/pci/vfio_pci_core.c    | 48 ++++++++++++++++++++++++-----
>  drivers/vfio/pci/vfio_pci_dmabuf.c  |  6 ++--
>  drivers/vfio/pci/vfio_pci_rdwr.c    | 42 +++++--------------------
>  drivers/vfio/pci/virtio/legacy_io.c | 13 ++++----
>  include/linux/vfio_pci_core.h       | 20 +++++++++++-
>  6 files changed, 91 insertions(+), 58 deletions(-)
> 

Applied 1/ and 2/ to the vfio for-linus branch for v7.1-rc.  My
intention is to have these merged for rc4, which I'll then use as the
base for the v7.2 queue where we can pull in 3/.  Thanks,

Alex