virtio_blk: set the zone write granularitygrafted

virtblk_read_zoned_limits() reads the write granularity that the device
reports in virtio_blk_zoned_characteristics and assigns it to the
physical block size and to io_min, but never to the limit that is named
after it. queue_limits.zone_write_granularity is left at zero, so
blk_validate_zoned_limits() raises it to the logical block size:

	if (lim->zone_write_granularity < lim->logical_block_size)
		lim->zone_write_granularity = lim->logical_block_size;

A device that reports a granularity coarser than its logical block size,
which is what the field exists to express, therefore has it silently
reduced. A 512e host managed disk passed through to a guest reports a
logical block size of 512 and a write granularity of 4096, and the guest
ends up with a zone write granularity of 512.

bio_split_alignment() returns lim->zone_write_granularity if it is non-zero
and bio_split_io_at() may split a bio with as per bio_split_alignment().
This can real to the write getting rejected by the host drive, as the write
is not aligned to the physical block size.

zonefs also takes its block size from bdev_zone_write_granularity(), so it
would incorrectly use 512 on a disk that requires 4096.

sd_zbc_read_zones() sets the limit from the physical block size for the
same reason. NVMe ZNS and null_blk leave it unset, but the fallback
gives the right answer for them, as their write granularity is the
logical block size. virtio carries a separate value that may exceed it.

Set the zone write granularity from the value that the device reports.

Fixes: 95bfec41bd3d ("virtio-blk: add support for zoned block devices")
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Link: https://patch.msgid.link/20260918140641.2031075-2-cassel@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 137 insertions, 0 deletions

diff --git a/Documentation/driver-api/generic_pt.rst b/Documentation/driver-api/generic_pt.rst
new file mode 100644
index 000000000..fd29d1b52
--- /dev/null
+++ b/Documentation/driver-api/generic_pt.rst
@@ -0,0 +1,137 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+========================
+Generic Radix Page Table
+========================
+
+.. kernel-doc:: include/linux/generic_pt/common.h
+	:doc: Generic Radix Page Table
+
+.. kernel-doc:: drivers/iommu/generic_pt/pt_defs.h
+	:doc: Generic Page Table Language
+
+Usage
+=====
+
+Generic PT is structured as a multi-compilation system. Since each format
+provides an API using a common set of names there can be only one format active
+within a compilation unit. This design avoids function pointers around the low
+level API.
+
+Instead the function pointers can end up at the higher level API (i.e.
+map/unmap, etc.) and the per-format code can be directly inlined into the
+per-format compilation unit. For something like IOMMU each format will be
+compiled into a per-format IOMMU operations kernel module.
+
+For this to work the .c file for each compilation unit will include both the
+format headers and the generic code for the implementation. For instance in an
+implementation compilation unit the headers would normally be included as
+follows:
+
+generic_pt/fmt/iommu_amdv1.c::
+
+	#include <linux/generic_pt/common.h>
+	#include "defs_amdv1.h"
+	#include "../pt_defs.h"
+	#include "amdv1.h"
+	#include "../pt_common.h"
+	#include "../pt_iter.h"
+	#include "../iommu_pt.h"  /* The IOMMU implementation */
+
+iommu_pt.h includes definitions that will generate the operations functions for
+map/unmap/etc. using the definitions provided by AMDv1. The resulting module
+will have exported symbols named like pt_iommu_amdv1_init().
+
+Refer to drivers/iommu/generic_pt/fmt/iommu_template.h for an example of how the
+IOMMU implementation uses multi-compilation to generate per-format ops structs
+pointers.
+
+The format code is written so that the common names arise from #defines to
+distinct format specific names. This is intended to aid debuggability by
+avoiding symbol clashes across all the different formats.
+
+Exported symbols and other global names are mangled using a per-format string
+via the NS() helper macro.
+
+The format uses struct pt_common as the top-level struct for the table,
+and each format will have its own struct pt_xxx which embeds it to store
+format-specific information.
+
+The implementation will further wrap struct pt_common in its own top-level
+struct, such as struct pt_iommu_amdv1.
+
+Format functions at the struct pt_common level
+----------------------------------------------
+
+.. kernel-doc:: include/linux/generic_pt/common.h
+	:identifiers:
+.. kernel-doc:: drivers/iommu/generic_pt/pt_common.h
+
+Iteration Helpers
+-----------------
+
+.. kernel-doc:: drivers/iommu/generic_pt/pt_iter.h
+
+Writing a Format
+----------------
+
+It is best to start from a simple format that is similar to the target. x86_64
+is usually a good reference for something simple, and AMDv1 is something fairly
+complete.
+
+The required inline functions need to be implemented in the format header.
+These should all follow the standard pattern of::
+
+ static inline pt_oaddr_t amdv1pt_entry_oa(const struct pt_state *pts)
+ {
+	[..]
+ }
+ #define pt_entry_oa amdv1pt_entry_oa
+
+where a uniquely named per-format inline function provides the implementation
+and a define maps it to the generic name. This is intended to make debug symbols
+work better. inline functions should always be used as the prototypes in
+pt_common.h will cause the compiler to validate the function signature to
+prevent errors.
+
+Review pt_fmt_defaults.h to understand some of the optional inlines.
+
+Once the format compiles then it should be run through the generic page table
+kunit test in kunit_generic_pt.h using kunit. For example::
+
+   $ tools/testing/kunit/kunit.py run --build_dir build_kunit_x86_64 --arch x86_64 --kunitconfig ./drivers/iommu/generic_pt/.kunitconfig amdv1_fmt_test.*
+   [...]
+   [11:15:08] Testing complete. Ran 9 tests: passed: 9
+   [11:15:09] Elapsed time: 3.137s total, 0.001s configuring, 2.368s building, 0.311s running
+
+The generic tests are intended to prove out the format functions and give
+clearer failures to speed up finding the problems. Once those pass then the
+entire kunit suite should be run.
+
+IOMMU Invalidation Features
+---------------------------
+
+Invalidation is how the page table algorithms synchronize with a HW cache of the
+page table memory, typically called the TLB (or IOTLB for IOMMU cases).
+
+The TLB can store present PTEs, non-present PTEs and table pointers, depending
+on its design. Every HW has its own approach on how to describe what has changed
+to have changed items removed from the TLB.
+
+PT_FEAT_FLUSH_RANGE
+~~~~~~~~~~~~~~~~~~~
+
+PT_FEAT_FLUSH_RANGE is the easiest scheme to understand. It tries to generate a
+single range invalidation for each operation, over-invalidating if there are
+gaps of VA that don't need invalidation. This trades off impacted VA for number
+of invalidation operations. It does not keep track of what is being invalidated;
+however, if pages have to be freed then page table pointers have to be cleaned
+from the walk cache. The range can start/end at any page boundary.
+
+PT_FEAT_FLUSH_RANGE_NO_GAPS
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+PT_FEAT_FLUSH_RANGE_NO_GAPS is similar to PT_FEAT_FLUSH_RANGE; however, it tries
+to minimize the amount of impacted VA by issuing extra flush operations. This is
+useful if the cost of processing VA is very high, for instance because a
+hypervisor is processing the page table with a shadowing algorithm.