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author | Alex Williamson <alex.williamson@redhat.com> | 2022-09-16 23:44:48 +0300 |
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committer | Bjorn Helgaas <bhelgaas@google.com> | 2022-10-05 20:21:02 +0300 |
commit | 91fa127794ac1c48069479b9d45eb4c7378c0e30 (patch) | |
tree | 7d5e75ed69ae94d812d65671c4ca421c6eb51d7e /Documentation/ABI/testing/sysfs-bus-pci | |
parent | 568035b01cfb107af8d2e4bd2fb9aea22cf5b868 (diff) | |
download | linux-91fa127794ac1c48069479b9d45eb4c7378c0e30.tar.xz |
PCI: Expose PCIe Resizable BAR support via sysfs
Add a simple sysfs interface to Resizable BAR support, largely for the
purposes of assigning such devices to a VM through VFIO. Resizable BARs
present a difficult feature to expose to a VM through emulation, as
resizing a BAR is done on the host. It can fail, and often does, but we
have no means via emulation of a PCIe REBAR capability to handle the error
cases.
A vfio-pci specific ioctl interface is also cumbersome as there are often
multiple devices within the same bridge aperture and handling them is a
challenge. In the interface proposed here, expanding a BAR potentially
requires such devices to be soft-removed during the resize operation and
rescanned after, in order for all the necessary resources to be released.
A pci-sysfs interface is also more universal than a vfio specific
interface.
Please see the ABI documentation update for usage.
Link: https://lore.kernel.org/r/166336088796.3597940.14973499936692558556.stgit@omen
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: Krzysztof Wilczyński <kw@linux.com>
Diffstat (limited to 'Documentation/ABI/testing/sysfs-bus-pci')
-rw-r--r-- | Documentation/ABI/testing/sysfs-bus-pci | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci index 6fc2c2efe8ab..840727fc75dc 100644 --- a/Documentation/ABI/testing/sysfs-bus-pci +++ b/Documentation/ABI/testing/sysfs-bus-pci @@ -457,3 +457,36 @@ Description: The file is writable if the PF is bound to a driver that implements ->sriov_set_msix_vec_count(). + +What: /sys/bus/pci/devices/.../resourceN_resize +Date: September 2022 +Contact: Alex Williamson <alex.williamson@redhat.com> +Description: + These files provide an interface to PCIe Resizable BAR support. + A file is created for each BAR resource (N) supported by the + PCIe Resizable BAR extended capability of the device. Reading + each file exposes the bitmap of available resource sizes: + + # cat resource1_resize + 00000000000001c0 + + The bitmap represents supported resource sizes for the BAR, + where bit0 = 1MB, bit1 = 2MB, bit2 = 4MB, etc. In the above + example the device supports 64MB, 128MB, and 256MB BAR sizes. + + When writing the file, the user provides the bit position of + the desired resource size, for example: + + # echo 7 > resource1_resize + + This indicates to set the size value corresponding to bit 7, + 128MB. The resulting size is 2 ^ (bit# + 20). This definition + matches the PCIe specification of this capability. + + In order to make use of resource resizing, all PCI drivers must + be unbound from the device and peer devices under the same + parent bridge may need to be soft removed. In the case of + VGA devices, writing a resize value will remove low level + console drivers from the device. Raw users of pci-sysfs + resourceN attributes must be terminated prior to resizing. + Success of the resizing operation is not guaranteed. |