On Thu, 17 Sep 2026 00:05:22 +0530
<[email protected]> wrote:
> From: Manish Honap <[email protected]>
>
> The MSI-X table is virtualized in vfio_pci_bar_rw() by an open-coded
> x_start/x_end window that fills reads with -1 and drops writes. Now that
> a generic excluded-range list expresses the same fill/drop behavior,
> register the MSI-X table as a read and write excluded range instead of
> special-casing it in the read/write path.
>
> Add the range when the MSI-X capability is parsed in
> vfio_pci_core_enable() and clear the list in vfio_pci_core_disable()
> alongside the config teardown. The read/write path now relies solely on
> vfio_pci_bar_find_exclusion(), so MSI-X and a provider's (e.g. vfio-cxl)
> trapped registers share one mechanism.
>
> No functional change.
>
> Assisted-by: LLM
> Signed-off-by: Manish Honap <[email protected]>
A few things inline that might tidy up the implementation and make
it a little more readable. Also you've use object allocators in some
places but not universally.
Jonathan
> ---
> drivers/vfio/pci/vfio_pci_core.c | 209 +++++++++++++++++++++++++++++++
> drivers/vfio/pci/vfio_pci_priv.h | 9 ++
> drivers/vfio/pci/vfio_pci_rdwr.c | 8 ++
> include/linux/vfio_pci_core.h | 14 +++
> 4 files changed, 240 insertions(+)
>
> diff --git a/drivers/vfio/pci/vfio_pci_core.c
> b/drivers/vfio/pci/vfio_pci_core.c
> index 9a75c30b67e2..9e4fa5d088a4 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -24,6 +24,7 @@
> #include <linux/pci.h>
> #include <linux/pm_runtime.h>
> #include <linux/slab.h>
> +#include <linux/sort.h>
> #include <linux/types.h>
> #include <linux/uaccess.h>
> #include <linux/vgaarb.h>
> @@ -1012,6 +1013,204 @@ static int msix_mmappable_cap(struct
> vfio_pci_core_device *vdev,
> return vfio_info_add_capability(caps, &header, sizeof(header));
> }
>
> +struct vfio_pci_excluded_range {
> + struct list_head entry;
> + int bar;
> + u64 start;
> + u64 size;
> + u32 flags;
> +};
> +
> +int vfio_pci_core_add_excluded_range(struct vfio_pci_core_device *vdev, int
> bar,
> + u64 start, u64 size, u32 flags)
> +{
> + struct vfio_pci_excluded_range *range;
> +
> + range = kzalloc_obj(*range);
> + if (!range)
> + return -ENOMEM;
> +
I'd be tempted to do kmalloc_obj and
*range = (struct vfio_pci_excluded_range) {
.bar = bar,
.start = start,
.size = size,
.flags = flags,
};
list_add_tail(...)
> + range->bar = bar;
> + range->start = start;
> + range->size = size;
> + range->flags = flags;
> + list_add_tail(&range->entry, &vdev->excluded_ranges);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(vfio_pci_core_add_excluded_range);
> +
> +static void vfio_pci_free_excluded_ranges(struct vfio_pci_core_device *vdev)
> +{
> + struct vfio_pci_excluded_range *range, *tmp;
> +
> + list_for_each_entry_safe(range, tmp, &vdev->excluded_ranges, entry) {
> + list_del(&range->entry);
> + kfree(range);
> + }
> +}
> +
> +/* A page-aligned mmap hole, derived from an mmap-excluded range. */
> +struct vfio_pci_mmap_hole {
> + u64 start;
> + u64 end;
> +};
This is just a range. Do we need another define for this specific case?
> +/*
> + * Advertise the BAR as mmappable minus every page-aligned mmap-excluded
> hole.
> + * A BAR can carry several holes at unrelated offsets (for example an MSI-X
> + * table and one or more trapped CXL component sub-blocks, which the CXL spec
> + * locates by pointer, not at fixed offsets).
> + * Collect the holes, page-align and sort them, coalesce any that overlap or
> + * touch, and advertise the gaps.
> + */
> +static int vfio_pci_excluded_sparse_cap(struct vfio_pci_core_device *vdev,
> + int index, struct vfio_info_cap *caps)
> +{
> + u64 bar_len = pci_resource_len(vdev->pdev, index);
> + struct vfio_region_info_cap_sparse_mmap *sparse;
> + struct vfio_pci_excluded_range *range;
> + struct vfio_pci_mmap_hole *holes;
> + int nr_holes = 0, nr_areas = 0, i, j;
Generally avoid mixing declarations with assignment with those that don't
on a single line. It is harder to read than splitting them into each
time of declaration.
> + size_t size;
> + u64 pos;
> + int ret;
> +
> + list_for_each_entry(range, &vdev->excluded_ranges, entry)
> + if (range->bar == index &&
> + (range->flags & VFIO_PCI_EXCLUDE_MMAP))
> + nr_holes++;
> +
> + if (!nr_holes)
> + return 0;
> +
struct vfio_pci_mmap_hole *holes __free(kfree) =
kzalloc_objs(*holes, nr_holes);
or something like that. Kees is well his way to getting rid of almost
all places where objects are allocated in non typesafe ways.
> + holes = kmalloc_array(nr_holes, sizeof(*holes), GFP_KERNEL);
> + if (!holes)
> + return -ENOMEM;
> +
> + /*
> + * mmap is page granular, so each hole rounds out to the page boundaries
> + * enclosing its excluded sub-range. The byte-granular exclusion still
> + * governs the fault and read/write paths; only the advertised mmap
> areas
> + * round to whole pages.
> + */
> + i = 0;
> + list_for_each_entry(range, &vdev->excluded_ranges, entry) {
> + if (range->bar != index ||
> + !(range->flags & VFIO_PCI_EXCLUDE_MMAP))
> + continue;
holes[i++] = (struct vfio_pci_mmap_hole) {
.start = ALIGN_DOWN(range->start, PAGE_SIZE),
.end = ALIGN(range->start + range->size, PAGE_SIZE),
};
Mind you vfio_pci_mmap_hole seems a lot like a range. So maybe just use a
struct range then you get
holes[i++] = DEFINE_RANGE(ALIGN_DOWN(range->start, PAGE_SIZE),
ALIGN(range->start + range->size,
PAGE_SIZE));
> + holes[i].start = ALIGN_DOWN(range->start, PAGE_SIZE);
> + holes[i].end = ALIGN(range->start + range->size, PAGE_SIZE);
> + i++;
> + }
> +
> + sort(holes, nr_holes, sizeof(*holes), vfio_pci_mmap_hole_cmp, NULL);
> +
> + /* Coalesce holes that overlap or touch after page alignment. */
> + for (i = 0, j = 0; i < nr_holes; i++) {
> + if (j && holes[i].start <= holes[j - 1].end)
> + holes[j - 1].end = max(holes[j - 1].end, holes[i].end);
> + else
> + holes[j++] = holes[i];
> + }
> + nr_holes = j;
> +
> + /* One mmappable area per gap: before, between, and after the holes. */
> + for (i = 0, pos = 0; i < nr_holes; i++) {
> + if (holes[i].start > pos)
> + nr_areas++;
> + pos = holes[i].end;
> + }
> + if (pos < bar_len)
> + nr_areas++;
> +
> + size = struct_size(sparse, areas, nr_areas);
struct vfio_region_info_cap_sparse_mmap *sparse =
kzalloc_flex(*sparse, areas, nr_areas);
> + sparse = kzalloc(size, GFP_KERNEL);
> + if (!sparse) {
> + kfree(holes);
with the __free above this can simply return.
> + return -ENOMEM;
> + }
> +
> + sparse->header.id = VFIO_REGION_INFO_CAP_SPARSE_MMAP;
> + sparse->header.version = 1;
> + sparse->nr_areas = nr_areas;
> +
> + for (i = 0, j = 0, pos = 0; i < nr_holes; i++) {
> + if (holes[i].start > pos) {
> + sparse->areas[j].offset = pos;
> + sparse->areas[j].size = holes[i].start - pos;
> + j++;
Bit of a long line because of the indent but I'd still go for setting whole
structure in one shot - so something like:
sparse->areas[j++] = (struct
vfio_region_sparse_mmap_area) {
.offset = pos,
.size = holes[i].start - pos,
};
> + }
> + pos = holes[i].end;
> + }
> + if (pos < bar_len) {
> + sparse->areas[j].offset = pos;
> + sparse->areas[j].size = bar_len - pos;
Similar for setting it in one go so we only do the indexing
once + looks more like above (where this trick is more advantageous!)
sparse->areas[j] = (struct vfio_sparse_mmap_area) {
.offset = pos,
.size = bar_len - pos,
};
> + }
> +
> + kfree(holes);
This looks like a good place to use __free magic to simplify things.
> + ret = vfio_info_add_capability(caps, &sparse->header, size);
> + kfree(sparse);
> + return ret;
> +}
> +
