> -----Original Message-----
> From: Jonathan Cameron <[email protected]>
> Sent: Saturday, September 26, 2026 3:35 AM
> To: Manish Honap <[email protected]>
> Cc: [email protected]; [email protected]; Ankit Agrawal <[email protected]>;
> [email protected]; [email protected]; Srirangan
> Madhavan <[email protected]>; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected]; Yishai
> Hadas <[email protected]>; Shameer Kolothum Thodi
> <[email protected]>; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected]; Neo Jia
> <[email protected]>; Krishnakant Jaju <[email protected]>; Vikram Sethi
> <[email protected]>; Zhi Wang <[email protected]>; linux-
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; linux-
> [email protected]; [email protected]
> Subject: Re: [PATCH v5 09/27] vfio/pci: Add a generic excluded-range list
>
> External email: Use caution opening links or attachments
>
>
> 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
Thank you; Alex asked on this patch for a sorted per-BAR list with
non-overlapping ranges and a two-pass build of the sparse capability,
which rewrites most of this code. The capability is then filled
straight from the list, so the holes array and struct
vfio_pci_mmap_hole go away, which also settles your struct range point.
In the code that remains, v6 will use kmalloc_obj(), kzalloc_flex() with
__free(kfree) for the sparse capability and separate declaration lines for
initialized and uninitialized variables as suggested.
>
> > ---
> > 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;
> > +}
> > +
>
