8000 PCI: Expose PCIe Resizable BAR support via sysfs · raspberrypi/linux@91fa127 · GitHub
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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>
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‎Documentation/ABI/testing/sysfs-bus-pci

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@@ -457,3 +457,36 @@ Description:
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The file is writable if the PF is bound to a driver that
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implements ->sriov_set_msix_vec_count().
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What: /sys/bus/pci/devices/.../resourceN_resize
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Date: September 2022
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Contact: Alex Williamson <alex.williamson@redhat.com>
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Description:
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These files provide an interface to PCIe Resizable BAR support.
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A file is created for each BAR resource (N) supported by the
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PCIe Resizable BAR extended capability of the device. Reading
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each file exposes the bitmap of available resource sizes:
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# cat resource1_resize
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00000000000001c0
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The bitmap represents supported resource sizes for the BAR,
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where bit0 = 1MB, bit1 = 2MB, bit2 = 4MB, etc. In the above
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example the device supports 64MB, 128MB, and 256MB BAR sizes.
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When writing the file, the user provides the bit position of
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the desired resource size, for example:
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# echo 7 > resource1_resize
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This indicates to set the size value corresponding to bit 7,
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128MB. The resulting size is 2 ^ (bit# + 20). This definition
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matches the PCIe specification of this capability.
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In order to make use of resource resizing, all PCI drivers must
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be unbound from the device and peer devices under the same
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parent bridge may need to be soft removed. In the case of
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VGA devices, writing a resize value will remove low level
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console drivers from the device. Raw users of pci-sysfs
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resourceN attributes must be terminated prior to resizing.
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Success of the resizing operation is not guaranteed.

‎drivers/pci/pci-sysfs.c

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@@ -28,6 +28,7 @@
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#include <linux/pm_runtime.h>
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#include <linux/msi.h>
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#include <linux/of.h>
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#include <linux/aperture.h>
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#include "pci.h"
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static int sysfs_initialized; /* = 0 */
@@ -1373,6 +1374,112 @@ static const struct attribute_group pci_dev_reset_attr_group = {
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.is_visible = pci_dev_reset_attr_is_visible,
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};
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#define pci_dev_resource_resize_attr(n) \
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static ssize_t resource##n##_resize_show(struct device *dev, \
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struct device_attribute *attr, \
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char * buf) \
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{ \
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struct pci_dev *pdev = to_pci_dev(dev); \
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ssize_t ret; \
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\
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pci_config_pm_runtime_get(pdev); \
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\
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ret = sysfs_emit(buf, "%016llx\n", \
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(u64)pci_rebar_get_possible_sizes(pdev, n)); \
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\
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pci_config_pm_runtime_put(pdev); \
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\
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return ret; \
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} \
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\
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static ssize_t resource##n##_resize_store(struct device *dev, \
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struct device_attribute *attr,\
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const char *buf, size_t count)\
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{ \
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struct pci_dev *pdev = to_pci_dev(dev); \
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unsigned long size, flags; \
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int ret, i; \
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u16 cmd; \
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\
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if (kstrtoul(buf, 0, &size) < 0) \
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return -EINVAL; \
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\
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device_lock(dev); \
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if (dev->driver) { \
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ret = -EBUSY; \
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goto unlock; \
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} \
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\
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pci_config_pm_runtime_get(pdev); \
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\
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if ((pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA) { \
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ret = aperture_remove_conflicting_pci_devices(pdev, \
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"resourceN_resize"); \
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if (ret) \
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goto pm_put; \
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} \
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\
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pci_read_config_word(pdev, PCI_COMMAND, &cmd); \
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pci_write_config_word(pdev, PCI_COMMAND, \
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cmd & ~PCI_COMMAND_MEMORY); \
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\
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flags = pci_resource_flags(pdev, n); \
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\
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pci_remove_resource_files(pdev); \
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\
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for (i = 0; i < PCI_STD_NUM_BARS; i++) { \
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if (pci_resource_len(pdev, i) && \
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pci_resource_flags(pdev, i) == flags) \
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pci_release_resource(pdev, i); \
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} \
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\
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ret = pci_resize_resource(pdev, n, size); \
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\
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pci_assign_unassigned_bus_resources(pdev->bus); \
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\
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if (pci_create_resource_files(pdev)) \
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pci_warn(pdev, "Failed to recreate resource files after BAR resizing\n");\
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\
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pci_write_config_word(pdev, PCI_COMMAND, cmd); \
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pm_put: \
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pci_config_pm_runtime_put(pdev); \
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unlock: \
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device_unlock(dev); \
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\
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return ret ? ret : count; \
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} \
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static DEVICE_ATTR_RW(resource##n##_resize)
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pci_dev_resource_resize_attr(0);
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pci_dev_resource_resize_attr(1);
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pci_dev_resource_resize_attr(2);
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pci_dev_resource_resize_attr(3);
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pci_dev_resource_resize_attr(4);
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pci_dev_resource_resize_attr(5);
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static struct attribute *resource_resize_attrs[] = {
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&dev_attr_resource0_resize.attr,
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&dev_attr_resource1_resize.attr,
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&dev_attr_resource2_resize.attr,
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&dev_attr_resource3_resize.attr,
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&dev_attr_resource4_resize.attr,
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&dev_attr_resource5_resize.attr,
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NULL,
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};
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static umode_t resource_resize_is_visible(struct kobject *kobj,
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struct attribute *a, int n)
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{
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struct pci_dev *pdev = to_pci_dev(kobj_to_dev(kobj));
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return pci_rebar_get_current_size(pdev, n) < 0 ? 0 : a->mode;
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}
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static const struct attribute_group pci_dev_resource_resize_group = {
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.attrs = resource_resize_attrs,
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.is_visible = resource_resize_is_visible,
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};
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int __must_check pci_create_sysfs_dev_files(struct pci_dev *pdev)
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{
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if (!sysfs_initialized)
@@ -1494,6 +1601,7 @@ const struct attribute_group *pci_dev_groups[] = {
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#ifdef CONFIG_ACPI
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&pci_dev_acpi_attr_group,
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#endif
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&pci_dev_resource_resize_group,
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NULL,
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};
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