Skip searching the software IO TLB if a device has never used it, making
sure these devices are not affected by the introduction of multiple IO TLB
memory pools.

Additional memory barrier is required to ensure that the new value of the
flag is visible to other CPUs after mapping a new bounce buffer. For
efficiency, the flag check should be inlined, and then the memory barrier
must be moved to is_swiotlb_buffer(). However, it can replace the existing
barrier in swiotlb_find_pool(), because all callers use is_swiotlb_buffer()
first to verify that the buffer address belongs to the software IO TLB.

Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

When swiotlb_find_slots() cannot find suitable slots, schedule the
allocation of a new memory pool. It is not possible to allocate the pool
immediately, because this code may run in interrupt context, which is not
suitable for large memory allocations. This means that the memory pool will
be available too late for the currently requested mapping, but the stress
on the software IO TLB allocator is likely to continue, and subsequent
allocations will benefit from the additional pool eventually.

Keep all memory pools for an allocator in an RCU list to avoid locking on
the read side. For modifications, add a new spinlock to struct io_tlb_mem.

The spinlock also protects updates to the total number of slabs (nslabs in
struct io_tlb_mem), but not reads of the value. Readers may therefore
encounter a stale value, but this is not an issue:

- swiotlb_tbl_map_single() and is_swiotlb_active() only check for non-zero
  value. This is ensured by the existence of the default memory pool,
  allocated at boot.

- The exact value is used only for non-critical purposes (debugfs, kernel
  messages).

Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

The value returned by default_swiotlb_limit() should be constant, because
it is used to decide whether DMA can be used. To allow allocating memory
pools on the fly, use the maximum possible physical address rather than the
highest address used by the default pool.

For swiotlb_init_remap(), this is either an arch-specific limit used by
memblock_alloc_low(), or the highest directly mapped physical address if
the initialization flags include SWIOTLB_ANY. For swiotlb_init_late(), the
highest address is determined by the GFP flags.

Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Try to allocate a transient memory pool if no suitable slots can be found
and the respective SWIOTLB is allowed to grow. The transient pool is just
enough big for this one bounce buffer. It is inserted into a per-device
list of transient memory pools, and it is freed again when the bounce
buffer is unmapped.

Transient memory pools are kept in an RCU list. A memory barrier is
required after adding a new entry, because any address within a transient
buffer must be immediately recognized as belonging to the SWIOTLB, even if
it is passed to another CPU.

Deletion does not require any synchronization beyond RCU ordering
guarantees. After a buffer is unmapped, its physical addresses may no
longer be passed to the DMA API, so the memory range of the corresponding
stale entry in the RCU list never matches. If the memory range gets
allocated again, then it happens only after a RCU quiescent state.

Since bounce buffers can now be allocated from different pools, add a
parameter to swiotlb_alloc_pool() to let the caller know which memory pool
is used. Add swiotlb_find_pool() to find the memory pool corresponding to
an address. This function is now also used by is_swiotlb_buffer(), because
a simple boundary check is no longer sufficient.

The logic in swiotlb_alloc_tlb() is taken from __dma_direct_alloc_pages(),
simplified and enhanced to use coherent memory pools if needed.

Note that this is not the most efficient way to provide a bounce buffer,
but when a DMA buffer can't be mapped, something may (and will) actually
break. At that point it is better to make an allocation, even if it may be
an expensive operation.

Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Add a config option (CONFIG_SWIOTLB_DYNAMIC) to enable or disable dynamic
allocation of additional bounce buffers.

If this option is set, mark the default SWIOTLB as able to grow and
restricted DMA pools as unable.

However, if the address of the default memory pool is explicitly queried,
make the default SWIOTLB also unable to grow. This is currently used to set
up PCI BAR movable regions on some Octeon MIPS boards which may not be able
to use a SWIOTLB pool elsewhere in physical memory. See octeon_pci_setup()
for more details.

If a remap function is specified, it must be also called on any dynamically
allocated pools, but there are some issues:

- The remap function may block, so it should not be called from an atomic
  context.
- There is no corresponding unremap() function if the memory pool is
  freed.
- The only in-tree implementation (xen_swiotlb_fixup) requires that the
  number of slots in the memory pool is a multiple of SWIOTLB_SEGSIZE.

Keep it simple for now and disable growing the SWIOTLB if a remap function
was specified.

Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Carve out memory pool specific fields from struct io_tlb_mem. The original
struct now contains shared data for the whole allocator, while the new
struct io_tlb_pool contains data that is specific to one memory pool of
(potentially) many.

Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Add some kernel-doc comments and move the existing documentation of struct
io_tlb_slot to its correct location. The latter was forgotten in commit
942a8186eb445 ("swiotlb: move struct io_tlb_slot to swiotlb.c").

Use the opportunity to give swiotlb_do_find_slots() a more descriptive name
and make it clear how it differs from swiotlb_find_slots().

Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

SWIOTLB implementation details should not be exposed to the rest of the
kernel. This will allow to make changes to the implementation without
modifying non-swiotlb code.

To avoid breaking existing users, provide helper functions for the few
required fields.

As a bonus, using a helper function to initialize struct device allows to
get rid of an #ifdef in driver core.

Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Commit 20347fca71a3 ("swiotlb: split up the global swiotlb lock") moved
the number of used slots to struct io_tlb_area, but it did not remove
the field from struct io_tlb_mem.

Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Pull dma-mapping updates from Christoph Hellwig:

 - fix a PageHighMem check in dma-coherent initialization (Doug Berger)

 - clean up the coherency defaul initialiation (Jiaxun Yang)

 - add cacheline to user/kernel dma-debug space dump messages (Desnes
   Nunes, Geert Uytterhoeve)

 - swiotlb statistics improvements (Michael Kelley)

 - misc cleanups (Petr Tesarik)

* tag 'dma-mapping-6.4-2023-04-28' of git://git.infradead.org/users/hch/dma-mapping:
  swiotlb: Omit total_used and used_hiwater if !CONFIG_DEBUG_FS
  swiotlb: track and report io_tlb_used high water marks in debugfs
  swiotlb: fix debugfs reporting of reserved memory pools
  swiotlb: relocate PageHighMem test away from rmem_swiotlb_setup
  of: address: always use dma_default_coherent for default coherency
  dma-mapping: provide CONFIG_ARCH_DMA_DEFAULT_COHERENT
  dma-mapping: provide a fallback dma_default_coherent
  dma-debug: Use %pa to format phys_addr_t
  dma-debug: add cacheline to user/kernel space dump messages
  dma-debug: small dma_debug_entry's comment and variable name updates
  dma-direct: cleanup parameters to dma_direct_optimal_gfp_mask