Re: [Intel-gfx] [PATCH v3 06/12] drm/ttm: Add a generic TTM memcpy move for page-based iomem

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On 5/25/21 11:18 AM, Matthew Auld wrote:
On Fri, 21 May 2021 at 16:33, Thomas Hellström
<thomas.hellstrom@xxxxxxxxxxxxxxx> wrote:
The internal ttm_bo_util memcpy uses ioremap functionality, and while it
probably might be possible to use it for copying in- and out of
sglist represented io memory, using io_mem_reserve() / io_mem_free()
callbacks, that would cause problems with fault().
Instead, implement a method mapping page-by-page using kmap_local()
semantics. As an additional benefit we then avoid the occasional global
TLB flushes of ioremap() and consuming ioremap space, elimination of a
critical point of failure and with a slight change of semantics we could
also push the memcpy out async for testing and async driver development
purposes.

A special linear iomem iterator is introduced internally to mimic the
old ioremap behaviour for code-paths that can't immediately be ported
over. This adds to the code size and should be considered a temporary
solution.

Looking at the code we have a lot of checks for iomap tagged pointers.
Ideally we should extend the core memremap functions to also accept
uncached memory and kmap_local functionality. Then we could strip a
lot of code.

Cc: Christian König <christian.koenig@xxxxxxx>
Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
---
v3:
- Split up in various TTM files and addressed review comments by
   Christian König. Tested and fixed legacy iomap memcpy path on i915.
---
  drivers/gpu/drm/ttm/ttm_bo_util.c  | 278 ++++++++++-------------------
  drivers/gpu/drm/ttm/ttm_module.c   |  35 ++++
  drivers/gpu/drm/ttm/ttm_resource.c | 166 +++++++++++++++++
  drivers/gpu/drm/ttm/ttm_tt.c       |  42 +++++
  include/drm/ttm/ttm_bo_driver.h    |  28 +++
  include/drm/ttm/ttm_caching.h      |   2 +
  include/drm/ttm/ttm_kmap_iter.h    |  61 +++++++
  include/drm/ttm/ttm_resource.h     |  61 +++++++
  include/drm/ttm/ttm_tt.h           |  16 ++
  9 files changed, 508 insertions(+), 181 deletions(-)
  create mode 100644 include/drm/ttm/ttm_kmap_iter.h

diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
index ae8b61460724..912cbe8e60a2 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -72,190 +72,126 @@ void ttm_mem_io_free(struct ttm_device *bdev,
         mem->bus.addr = NULL;
  }

-static int ttm_resource_ioremap(struct ttm_device *bdev,
-                              struct ttm_resource *mem,
-                              void **virtual)
+/**
+ * ttm_move_memcpy - Helper to perform a memcpy ttm move operation.
+ * @bo: The struct ttm_buffer_object.
+ * @new_mem: The struct ttm_resource we're moving to (copy destination).
+ * @new_iter: A struct ttm_kmap_iter representing the destination resource.
+ * @src_iter: A struct ttm_kmap_iter representing the source resource.
+ *
+ * This function is intended to be able to move out async under a
+ * dma-fence if desired.
+ */
+void ttm_move_memcpy(struct ttm_buffer_object *bo,
+                    struct ttm_resource *dst_mem,
+                    struct ttm_kmap_iter *dst_iter,
+                    struct ttm_kmap_iter *src_iter)
  {
-       int ret;
-       void *addr;
-
-       *virtual = NULL;
-       ret = ttm_mem_io_reserve(bdev, mem);
-       if (ret || !mem->bus.is_iomem)
-               return ret;
+       const struct ttm_kmap_iter_ops *dst_ops = dst_iter->ops;
+       const struct ttm_kmap_iter_ops *src_ops = src_iter->ops;
+       struct ttm_tt *ttm = bo->ttm;
+       struct dma_buf_map src_map, dst_map;
+       pgoff_t i;

-       if (mem->bus.addr) {
-               addr = mem->bus.addr;
-       } else {
-               size_t bus_size = (size_t)mem->num_pages << PAGE_SHIFT;
+       /* Single TTM move. NOP */
+       if (dst_ops->maps_tt && src_ops->maps_tt)
+               return;

-               if (mem->bus.caching == ttm_write_combined)
-                       addr = ioremap_wc(mem->bus.offset, bus_size);
-#ifdef CONFIG_X86
-               else if (mem->bus.caching == ttm_cached)
-                       addr = ioremap_cache(mem->bus.offset, bus_size);
-#endif
-               else
-                       addr = ioremap(mem->bus.offset, bus_size);
-               if (!addr) {
-                       ttm_mem_io_free(bdev, mem);
-                       return -ENOMEM;
+       /* Don't move nonexistent data. Clear destination instead. */
+       if (src_ops->maps_tt && (!ttm || !ttm_tt_is_populated(ttm))) {
+               if (ttm && !(ttm->page_flags & TTM_PAGE_FLAG_ZERO_ALLOC))
+                       return;
+
+               for (i = 0; i < dst_mem->num_pages; ++i) {
+                       dst_ops->map_local(dst_iter, &dst_map, i);
+                       if (dst_map.is_iomem)
+                               memset_io(dst_map.vaddr_iomem, 0, PAGE_SIZE);
+                       else
+                               memset(dst_map.vaddr, 0, PAGE_SIZE);
+                       if (dst_ops->unmap_local)
+                               dst_ops->unmap_local(dst_iter, &dst_map);
                 }
+               return;
         }
-       *virtual = addr;
-       return 0;
-}
-
-static void ttm_resource_iounmap(struct ttm_device *bdev,
-                               struct ttm_resource *mem,
-                               void *virtual)
-{
-       if (virtual && mem->bus.addr == NULL)
-               iounmap(virtual);
-       ttm_mem_io_free(bdev, mem);
-}
-
-static int ttm_copy_io_page(void *dst, void *src, unsigned long page)
-{
-       uint32_t *dstP =
-           (uint32_t *) ((unsigned long)dst + (page << PAGE_SHIFT));
-       uint32_t *srcP =
-           (uint32_t *) ((unsigned long)src + (page << PAGE_SHIFT));
-
-       int i;
-       for (i = 0; i < PAGE_SIZE / sizeof(uint32_t); ++i)
-               iowrite32(ioread32(srcP++), dstP++);
-       return 0;
-}
-
-static int ttm_copy_io_ttm_page(struct ttm_tt *ttm, void *src,
-                               unsigned long page,
-                               pgprot_t prot)
-{
-       struct page *d = ttm->pages[page];
-       void *dst;
-
-       if (!d)
-               return -ENOMEM;
-
-       src = (void *)((unsigned long)src + (page << PAGE_SHIFT));
-       dst = kmap_atomic_prot(d, prot);
-       if (!dst)
-               return -ENOMEM;
-
-       memcpy_fromio(dst, src, PAGE_SIZE);
-
-       kunmap_atomic(dst);
-
-       return 0;
-}
-
-static int ttm_copy_ttm_io_page(struct ttm_tt *ttm, void *dst,
-                               unsigned long page,
-                               pgprot_t prot)
-{
-       struct page *s = ttm->pages[page];
-       void *src;
-
-       if (!s)
-               return -ENOMEM;
-
-       dst = (void *)((unsigned long)dst + (page << PAGE_SHIFT));
-       src = kmap_atomic_prot(s, prot);
-       if (!src)
-               return -ENOMEM;

-       memcpy_toio(dst, src, PAGE_SIZE);
-
-       kunmap_atomic(src);
+       for (i = 0; i < dst_mem->num_pages; ++i) {
+               dst_ops->map_local(dst_iter, &dst_map, i);
+               src_ops->map_local(src_iter, &src_map, i);
+
+               if (!src_map.is_iomem && !dst_map.is_iomem) {
+                       memcpy(dst_map.vaddr, src_map.vaddr, PAGE_SIZE);
+               } else if (!src_map.is_iomem) {
+                       dma_buf_map_memcpy_to(&dst_map, src_map.vaddr,
+                                             PAGE_SIZE);
+               } else if (!dst_map.is_iomem) {
+                       memcpy_fromio(dst_map.vaddr, src_map.vaddr_iomem,
+                                     PAGE_SIZE);
+               } else {
+                       int j;
+                       u32 __iomem *src = src_map.vaddr_iomem;
+                       u32 __iomem *dst = dst_map.vaddr_iomem;

-       return 0;
+                       for (j = 0; j < (PAGE_SIZE >> 2); ++j)
IMO PAGE_SIZE / sizeof(u32) is easier to understand.

OK, will fix.



+                               iowrite32(ioread32(src++), dst++);
+               }
+               if (src_ops->unmap_local)
+                       src_ops->unmap_local(src_iter, &src_map);
+               if (dst_ops->unmap_local)
+                       dst_ops->unmap_local(dst_iter, &dst_map);
+       }
  }
+EXPORT_SYMBOL(ttm_move_memcpy);

  int ttm_bo_move_memcpy(struct ttm_buffer_object *bo,
                        struct ttm_operation_ctx *ctx,
-                      struct ttm_resource *new_mem)
+                      struct ttm_resource *dst_mem)
  {
         struct ttm_device *bdev = bo->bdev;
-       struct ttm_resource_manager *man = ttm_manager_type(bdev, new_mem->mem_type);
+       struct ttm_resource_manager *dst_man =
+               ttm_manager_type(bo->bdev, dst_mem->mem_type);
         struct ttm_tt *ttm = bo->ttm;
-       struct ttm_resource *old_mem = &bo->mem;
-       struct ttm_resource old_copy = *old_mem;
-       void *old_iomap;
-       void *new_iomap;
+       struct ttm_resource *src_mem = &bo->mem;
+       struct ttm_resource_manager *src_man =
+               ttm_manager_type(bdev, src_mem->mem_type);
+       struct ttm_resource src_copy = *src_mem;
+       union {
+               struct ttm_kmap_iter_tt tt;
+               struct ttm_kmap_iter_linear_io io;
+       } _dst_iter, _src_iter;
+       struct ttm_kmap_iter *dst_iter, *src_iter;
         int ret;
-       unsigned long i;

-       ret = ttm_bo_wait_ctx(bo, ctx);
-       if (ret)
-               return ret;
-
-       ret = ttm_resource_ioremap(bdev, old_mem, &old_iomap);
-       if (ret)
-               return ret;
-       ret = ttm_resource_ioremap(bdev, new_mem, &new_iomap);
-       if (ret)
-               goto out;
-
-       /*
-        * Single TTM move. NOP.
-        */
-       if (old_iomap == NULL && new_iomap == NULL)
-               goto out2;
-
-       /*
-        * Don't move nonexistent data. Clear destination instead.
-        */
-       if (old_iomap == NULL &&
-           (ttm == NULL || (!ttm_tt_is_populated(ttm) &&
-                            !(ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)))) {
-               memset_io(new_iomap, 0, new_mem->num_pages*PAGE_SIZE);
-               goto out2;
-       }
-
-       /*
-        * TTM might be null for moves within the same region.
-        */
-       if (ttm) {
+       if (ttm && ((ttm->page_flags & TTM_PAGE_FLAG_SWAPPED) ||
+                   dst_man->use_tt)) {
                 ret = ttm_tt_populate(bdev, ttm, ctx);
                 if (ret)
-                       goto out1;
+                       return ret;
         }

-       for (i = 0; i < new_mem->num_pages; ++i) {
-               if (old_iomap == NULL) {
-                       pgprot_t prot = ttm_io_prot(bo, old_mem, PAGE_KERNEL);
-                       ret = ttm_copy_ttm_io_page(ttm, new_iomap, i,
-                                                  prot);
-               } else if (new_iomap == NULL) {
-                       pgprot_t prot = ttm_io_prot(bo, new_mem, PAGE_KERNEL);
-                       ret = ttm_copy_io_ttm_page(ttm, old_iomap, i,
-                                                  prot);
-               } else {
-                       ret = ttm_copy_io_page(new_iomap, old_iomap, i);
-               }
-               if (ret)
-                       goto out1;
+       dst_iter = ttm_kmap_iter_linear_io_init(&_dst_iter.io, bdev, dst_mem);
+       if (PTR_ERR(dst_iter) == -EINVAL && dst_man->use_tt)
+               dst_iter = ttm_kmap_iter_tt_init(&_dst_iter.tt, bo->ttm);
+       if (IS_ERR(dst_iter))
+               return PTR_ERR(dst_iter);
+
+       src_iter = ttm_kmap_iter_linear_io_init(&_src_iter.io, bdev, src_mem);
+       if (PTR_ERR(src_iter) == -EINVAL && src_man->use_tt)
+               src_iter = ttm_kmap_iter_tt_init(&_src_iter.tt, bo->ttm);
+       if (IS_ERR(src_iter)) {
+               ret = PTR_ERR(src_iter);
+               goto out_src_iter;
         }
-       mb();
-out2:
-       old_copy = *old_mem;

-       ttm_bo_assign_mem(bo, new_mem);
-
-       if (!man->use_tt)
-               ttm_bo_tt_destroy(bo);
+       ttm_move_memcpy(bo, dst_mem, dst_iter, src_iter);
+       src_copy = *src_mem;
+       ttm_bo_move_sync_cleanup(bo, dst_mem);

-out1:
-       ttm_resource_iounmap(bdev, old_mem, new_iomap);
-out:
-       ttm_resource_iounmap(bdev, &old_copy, old_iomap);
+       if (!src_iter->ops->maps_tt)
+               ttm_kmap_iter_linear_io_fini(&_src_iter.io, bdev, &src_copy);
+out_src_iter:
+       if (!dst_iter->ops->maps_tt)
+               ttm_kmap_iter_linear_io_fini(&_dst_iter.io, bdev, dst_mem);

-       /*
-        * On error, keep the mm node!
-        */
-       if (!ret)
-               ttm_resource_free(bo, &old_copy);
         return ret;
  }
  EXPORT_SYMBOL(ttm_bo_move_memcpy);
@@ -336,27 +272,7 @@ pgprot_t ttm_io_prot(struct ttm_buffer_object *bo, struct ttm_resource *res,
         man = ttm_manager_type(bo->bdev, res->mem_type);
         caching = man->use_tt ? bo->ttm->caching : res->bus.caching;

-       /* Cached mappings need no adjustment */
-       if (caching == ttm_cached)
-               return tmp;
-
-#if defined(__i386__) || defined(__x86_64__)
-       if (caching == ttm_write_combined)
-               tmp = pgprot_writecombine(tmp);
-       else if (boot_cpu_data.x86 > 3)
-               tmp = pgprot_noncached(tmp);
-#endif
-#if defined(__ia64__) || defined(__arm__) || defined(__aarch64__) || \
-    defined(__powerpc__) || defined(__mips__)
-       if (caching == ttm_write_combined)
-               tmp = pgprot_writecombine(tmp);
-       else
-               tmp = pgprot_noncached(tmp);
-#endif
-#if defined(__sparc__)
-       tmp = pgprot_noncached(tmp);
-#endif
-       return tmp;
+       return ttm_prot_from_caching(caching, tmp);
  }
  EXPORT_SYMBOL(ttm_io_prot);

diff --git a/drivers/gpu/drm/ttm/ttm_module.c b/drivers/gpu/drm/ttm/ttm_module.c
index 56b0efdba1a9..997c458f68a9 100644
--- a/drivers/gpu/drm/ttm/ttm_module.c
+++ b/drivers/gpu/drm/ttm/ttm_module.c
@@ -31,12 +31,47 @@
   */
  #include <linux/module.h>
  #include <linux/device.h>
+#include <linux/pgtable.h>
  #include <linux/sched.h>
  #include <linux/debugfs.h>
  #include <drm/drm_sysfs.h>
+#include <drm/ttm/ttm_caching.h>

  #include "ttm_module.h"

+/**
+ * ttm_prot_from_caching - Modify the page protection according to the
+ * ttm cacing mode
+ * @caching: The ttm caching mode
+ * @tmp: The original page protection
+ *
+ * Return: The modified page protection
+ */
+pgprot_t ttm_prot_from_caching(enum ttm_caching caching, pgprot_t tmp)
+{
+       /* Cached mappings need no adjustment */
+       if (caching == ttm_cached)
+               return tmp;
+
+#if defined(__i386__) || defined(__x86_64__)
+       if (caching == ttm_write_combined)
+               tmp = pgprot_writecombine(tmp);
+       else if (boot_cpu_data.x86 > 3)
+               tmp = pgprot_noncached(tmp);
+#endif
+#if defined(__ia64__) || defined(__arm__) || defined(__aarch64__) || \
+       defined(__powerpc__) || defined(__mips__)
+       if (caching == ttm_write_combined)
+               tmp = pgprot_writecombine(tmp);
+       else
+               tmp = pgprot_noncached(tmp);
+#endif
+#if defined(__sparc__)
+       tmp = pgprot_noncached(tmp);
+#endif
+       return tmp;
+}
+
  struct dentry *ttm_debugfs_root;

  static int __init ttm_init(void)
diff --git a/drivers/gpu/drm/ttm/ttm_resource.c b/drivers/gpu/drm/ttm/ttm_resource.c
index 59e2b7157e41..e05ae7e3d477 100644
--- a/drivers/gpu/drm/ttm/ttm_resource.c
+++ b/drivers/gpu/drm/ttm/ttm_resource.c
@@ -22,6 +22,10 @@
   * Authors: Christian König
   */

+#include <linux/dma-buf-map.h>
+#include <linux/io-mapping.h>
+#include <linux/scatterlist.h>
+
  #include <drm/ttm/ttm_resource.h>
  #include <drm/ttm/ttm_bo_driver.h>

@@ -147,3 +151,165 @@ void ttm_resource_manager_debug(struct ttm_resource_manager *man,
                 man->func->debug(man, p);
  }
  EXPORT_SYMBOL(ttm_resource_manager_debug);
+
+static void ttm_kmap_iter_iomap_map_local(struct ttm_kmap_iter *iter,
+                                         struct dma_buf_map *dmap,
+                                         pgoff_t i)
+{
+       struct ttm_kmap_iter_iomap *iter_io =
+               container_of(iter, typeof(*iter_io), base);
+       void __iomem *addr;
+
+retry:
+       while (i >= iter_io->cache.end) {
+               iter_io->cache.sg = iter_io->cache.sg ?
+                       sg_next(iter_io->cache.sg) : iter_io->st->sgl;
+               iter_io->cache.i = iter_io->cache.end;
+               iter_io->cache.end += sg_dma_len(iter_io->cache.sg) >>
+                       PAGE_SHIFT;
+               iter_io->cache.offs = sg_dma_address(iter_io->cache.sg) -
+                       iter_io->start;
+       }
+
+       if (i < iter_io->cache.i) {
+               iter_io->cache.end = 0;
+               iter_io->cache.sg = NULL;
+               goto retry;
+       }
+
+       addr = io_mapping_map_local_wc(iter_io->iomap, iter_io->cache.offs +
+                                      (((resource_size_t)i - iter_io->cache.i)
+                                       << PAGE_SHIFT));
+       dma_buf_map_set_vaddr_iomem(dmap, addr);
+}
+
+static void ttm_kmap_iter_iomap_unmap_local(struct ttm_kmap_iter *iter,
+                                           struct dma_buf_map *map)
+{
+       io_mapping_unmap_local(map->vaddr_iomem);
+}
+
+static const struct ttm_kmap_iter_ops ttm_kmap_iter_io_ops = {
+       .map_local =  ttm_kmap_iter_iomap_map_local,
+       .unmap_local = ttm_kmap_iter_iomap_unmap_local,
+       .maps_tt = false,
+};
+
+/**
+ * ttm_kmap_iter_iomap_init - Initialize a struct ttm_kmap_iter_iomap
+ * @iter_io: The struct ttm_kmap_iter_iomap to initialize.
+ * @iomap: The struct io_mapping representing the underlying linear io_memory.
+ * @st: sg_table into @iomap, representing the memory of the struct
+ * ttm_resource.
+ * @start: Offset that needs to be subtracted from @st to make
+ * sg_dma_address(st->sgl) - @start == 0 for @iomap start.
+ *
+ * Return: Pointer to the embedded struct ttm_kmap_iter.
+ */
+struct ttm_kmap_iter *
+ttm_kmap_iter_iomap_init(struct ttm_kmap_iter_iomap *iter_io,
+                        struct io_mapping *iomap,
+                        struct sg_table *st,
+                        resource_size_t start)
+{
+       iter_io->base.ops = &ttm_kmap_iter_io_ops;
+       iter_io->iomap = iomap;
+       iter_io->st = st;
+       iter_io->start = start;
+       memset(&iter_io->cache, 0, sizeof(iter_io->cache));
+
+       return &iter_io->base;
+}
+EXPORT_SYMBOL(ttm_kmap_iter_iomap_init);
+
+/**
+ * DOC: Linear io iterator
+ *
+ * This code should die in the not too near future. Best would be if we could
+ * make io-mapping use memremap for all io memory, and have memremap
+ * implement a kmap_local functionality. We could then strip a huge amount of
+ * code. These linear io iterators are implemented to mimic old functionality,
+ * and they don't use kmap_local semantics at all internally. Rather ioremap or
+ * friends, and at least on 32-bit they add global TLB flushes and points
+ * of failure.
+ */
+
+static void ttm_kmap_iter_linear_io_map_local(struct ttm_kmap_iter *iter,
+                                             struct dma_buf_map *dmap,
+                                             pgoff_t i)
+{
+       struct ttm_kmap_iter_linear_io *iter_io =
+               container_of(iter, typeof(*iter_io), base);
+
+       *dmap = iter_io->dmap;
+       dma_buf_map_incr(dmap, i * PAGE_SIZE);
+}
+
+static const struct ttm_kmap_iter_ops ttm_kmap_iter_linear_io_ops = {
+       .map_local =  ttm_kmap_iter_linear_io_map_local,
+       .maps_tt = false,
+};
+
+struct ttm_kmap_iter *
+ttm_kmap_iter_linear_io_init(struct ttm_kmap_iter_linear_io *iter_io,
+                            struct ttm_device *bdev,
+                            struct ttm_resource *mem)
+{
+       int ret;
+
+       ret = ttm_mem_io_reserve(bdev, mem);
+       if (ret)
+               goto out_err;
+       if (!mem->bus.is_iomem) {
+               ret = -EINVAL;
+               goto out_io_free;
+       }
+
+       if (mem->bus.addr) {
+               dma_buf_map_set_vaddr(&iter_io->dmap, mem->bus.addr);
+               iter_io->needs_unmap = false;
+       } else {
+               size_t bus_size = (size_t)mem->num_pages << PAGE_SHIFT;
+
+               iter_io->needs_unmap = true;
+               if (mem->bus.caching == ttm_write_combined)
+                       dma_buf_map_set_vaddr_iomem(&iter_io->dmap,
+                                                   ioremap_wc(mem->bus.offset,
+                                                              bus_size));
+               else if (mem->bus.caching == ttm_cached)
+                       dma_buf_map_set_vaddr(&iter_io->dmap,
+                                             memremap(mem->bus.offset, bus_size,
+                                                      MEMREMAP_WB));
The comments in set_vaddr suggest that this is meant for
system-memory. Does that actually matter or is it just about not
losing the __iomem annotation on platforms where it matters?

Yes, it's the latter. dma_buf_map() is relatively new and the author probably didn't think about the case of cached iomem, which is used by, for example, vmwgfx.

Apparently cached device local is a thing. Also should this not be
wrapped in CONFIG_X86?

Both dma_buf_map() and memremap are generic, I think, I guess memremap would return NULL if it's not supported.

/Thomas





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