Introduce the ability to queue p2m mapping operations in vPCI. This is
pre-requisite for both vPCI SR-IOV [2] and the ability to handle BAR writes
with memory decoding enabled [1]. I thought I might wait to submit the BAR-
write-with-memory-decoding-enabled patch until the prerequisite is reviewed
acked/merged, but if you'd find it more helpful for me to submit it right away
I'd be happy to do so (I've already pushed it to the gitlab pipeline [0]).

When multiple operations are queued, there are some non-trivial complexities
with the deferred setting of bar->enabled, header->rom_enabled, and
header->bars_mapped flags. If deferred, these flags wouldn't be updated until
the p2m op queue is processing, but we need to consult them in modify_bars()
at queue time, so they wouldn't be accurate when adding multiple tasks to the
queue. In order to simplify the deferred mapping state, and in particular
avoid complexities with the bar->enabled, header->rom_enabled, and
header->bars_mapped flags, I have picked up Roger's vPCI fixes series [3]. The
overall result is now that _only_ p2m operations are deferred. PCI config
space writes, flag-setting, and everything else is handled at queuing time.

1. vpci: move BAR mapping permissions checks
2. vpci: make BAR mapping more resilient for the hardware domain
3. vpci: only check BAR validity once
4. vpci/msix: move MSI-X hole punching as a result of memory decoding enable
5. vpci: simplify handling of memory decoding and ROM enable writes
6. vpci: create mem local variables
7. vpci: split vpci_process_pending()
8. vpci: allow queueing of mapping operations
9. vpci: don't pass command value to modify_bars()

Patch 1 is code movement, and patch 2 is hardening map_range(). While these
 first 2 are not strictly pre-requisites for queued mapping, they simplify the
 subsequent prepwork.
Patches 3-5 progressively remove modify_decoding().
Patches 6-7 are non-functional changes pulled out from patch 8.
Patch 8 is the core feature: pre-requisite for SR-IOV and BAR-write-with-
 memory-decoding-enabled.
Patch 9 is cleanup I chose to put at the end for lower diffstat.

Patches 2-5 are borrowed from Roger's vPCI fixes series [3]. These patches
have gone directly from v1 to v5, but otherwise revlogs are written assuming
this is a continuation of the BAR-write-with-memory-decoding-enabled series.

v4->v5:
* don't defer anything that's not p2m related
* drop ("vpci: allow 32-bit BAR writes with memory decoding enabled") for now
  to focus on the pre-requisite patches first
* split non-functional changes

v3->v4:
* switch back to dynamically allocated queue elements

v2->v3:
* add ("vpci: Use pervcpu ranges for BAR mapping")
* rework with fixed array of map/unmap slots

v1->v2:
* new approach with queued p2m operations

RFC->v1:
* rework BAR mapping machinery to support unmap-then-map operation

[0] Pipeline: https://gitlab.com/xen-project/people/stewarthildebrand/xen/-/pipelines/2662651745

[1] BAR write with memory decoding enabled
v4: https://lore.kernel.org/xen-devel/20260406191203.97662-1-stewart.hildebrand@amd.com/T/#t
v3: https://lore.kernel.org/xen-devel/20260324030513.700217-1-stewart.hildebrand@amd.com/T/#t
v2: https://lore.kernel.org/xen-devel/20250723163744.13095-1-stewart.hildebrand@amd.com/T/#t
v1: https://lore.kernel.org/xen-devel/20250531125405.268984-1-stewart.hildebrand@amd.com/T/#t
RFC: https://lore.kernel.org/xen-devel/20250312195019.382926-1-stewart.hildebrand@amd.com/T/#t
Gitlab: https://gitlab.com/xen-project/xen/-/issues/197

[2] vPCI SR-IOV
v3: https://lore.kernel.org/xen-devel/cover.1775742115.git.mykyta_poturai@epam.com/T/#t
v2: https://lore.kernel.org/xen-devel/cover.1772806036.git.mykyta_poturai@epam.com/T/#t
v1: https://lore.kernel.org/xen-devel/cover.1753450965.git.mykyta_poturai@epam.com/T/#t
2018 v2 https://lore.kernel.org/xen-devel/20180717094830.54806-1-roger.pau@citrix.com/T/#t

[3] vPCI miscellaneous fixes
https://lore.kernel.org/xen-devel/20250814160358.95543-1-roger.pau@citrix.com/T/#t


 xen/common/domain.c        |   5 +
 xen/drivers/vpci/header.c  | 443 +++++++++++++++++++++----------------
 xen/drivers/vpci/private.h |   1 +
 xen/drivers/vpci/vpci.c    |  17 +-
 xen/include/xen/vpci.h     |  15 +-
 5 files changed, 279 insertions(+), 202 deletions(-)


base-commit: 03851197a7b2cd58851b9ec2293bdf4a68c47b66
-- 
2.54.0