From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Daniel Axtens <dja@axtens.net>

Date: Thu, 21 Apr 2022 15:24:15 +1000

Subject: [PATCH] mm: When adding a region, merge with region after as well as

 before

On x86_64-efi (at least) regions seem to be added from top down. The mm

code will merge a new region with an existing region that comes

immediately before the new region. This allows larger allocations to be

satisfied that would otherwise be the case.

On powerpc-ieee1275, however, regions are added from bottom up. So if

we add 3x 32MB regions, we can still only satisfy a 32MB allocation,

rather than the 96MB allocation we might otherwise be able to satisfy.

  * Define 'post_size' as being bytes lost to the end of an allocation

    due to being given weird sizes from firmware that are not multiples

    of GRUB_MM_ALIGN.

  * Allow merging of regions immediately _after_ existing regions, not

    just before. As with the other approach, we create an allocated

    block to represent the new space and the pass it to grub_free() to

    get the metadata right.

Signed-off-by: Daniel Axtens <dja@axtens.net>

Tested-by: Stefan Berger <stefanb@linux.ibm.com>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Tested-by: Patrick Steinhardt <ps@pks.im>

(cherry picked from commit 052e6068be622ff53f1238b449c300dbd0a8abcd)

---

 grub-core/kern/mm.c       | 128 +++++++++++++++++++++++++++++-----------------

 include/grub/mm_private.h |   9 ++++

 2 files changed, 91 insertions(+), 46 deletions(-)

diff --git a/grub-core/kern/mm.c b/grub-core/kern/mm.c

index 1cbf98c7ab..7be33e23bf 100644

--- a/grub-core/kern/mm.c

+++ b/grub-core/kern/mm.c

@@ -130,53 +130,88 @@ grub_mm_init_region (void *addr, grub_size_t size)

   /* Attempt to merge this region with every existing region */

   for (p = &grub_mm_base, q = *p; q; p = &(q->next), q = *p)

-    /*

-     * Is the new region immediately below an existing region? That

-     * is, is the address of the memory we're adding now (addr) + size

-     * of the memory we're adding (size) + the bytes we couldn't use

-     * at the start of the region we're considering (q->pre_size)

-     * equal to the address of q? In other words, does the memory

-     * looks like this?

-     *

-     * addr                          q

-     *   |----size-----|-q->pre_size-|<q region>|

-     */

-    if ((grub_uint8_t *) addr + size + q->pre_size == (grub_uint8_t *) q)

-      {

-	/*

-	 * Yes, we can merge the memory starting at addr into the

-	 * existing region from below. Align up addr to GRUB_MM_ALIGN

-	 * so that our new region has proper alignment.

-	 */

-	r = (grub_mm_region_t) ALIGN_UP ((grub_addr_t) addr, GRUB_MM_ALIGN);

-	/* Copy the region data across */

-	*r = *q;

-	/* Consider all the new size as pre-size */

-	r->pre_size += size;

+    {

+      /*

+       * Is the new region immediately below an existing region? That

+       * is, is the address of the memory we're adding now (addr) + size

+       * of the memory we're adding (size) + the bytes we couldn't use

+       * at the start of the region we're considering (q->pre_size)

+       * equal to the address of q? In other words, does the memory

+       * looks like this?

+       *

+       * addr                          q

+       *   |----size-----|-q->pre_size-|<q region>|

+       */

+      if ((grub_uint8_t *) addr + size + q->pre_size == (grub_uint8_t *) q)

+        {

+          /*

+           * Yes, we can merge the memory starting at addr into the

+           * existing region from below. Align up addr to GRUB_MM_ALIGN

+           * so that our new region has proper alignment.

+           */

+          r = (grub_mm_region_t) ALIGN_UP ((grub_addr_t) addr, GRUB_MM_ALIGN);

+          /* Copy the region data across */

+          *r = *q;

+          /* Consider all the new size as pre-size */

+          r->pre_size += size;

-	/*

-	 * If we have enough pre-size to create a block, create a

-	 * block with it. Mark it as allocated and pass it to

-	 * grub_free (), which will sort out getting it into the free

-	 * list.

-	 */

-	if (r->pre_size >> GRUB_MM_ALIGN_LOG2)

-	  {

-	    h = (grub_mm_header_t) (r + 1);

-	    /* block size is pre-size converted to cells */

-	    h->size = (r->pre_size >> GRUB_MM_ALIGN_LOG2);

-	    h->magic = GRUB_MM_ALLOC_MAGIC;

-	    /* region size grows by block size converted back to bytes */

-	    r->size += h->size << GRUB_MM_ALIGN_LOG2;

-	    /* adjust pre_size to be accurate */

-	    r->pre_size &= (GRUB_MM_ALIGN - 1);

-	    *p = r;

-	    grub_free (h + 1);

-	  }

-	/* Replace the old region with the new region */

-	*p = r;

-	return;

-      }

+          /*

+           * If we have enough pre-size to create a block, create a

+           * block with it. Mark it as allocated and pass it to

+           * grub_free (), which will sort out getting it into the free

+           * list.

+           */

+          if (r->pre_size >> GRUB_MM_ALIGN_LOG2)

+            {

+              h = (grub_mm_header_t) (r + 1);

+              /* block size is pre-size converted to cells */

+              h->size = (r->pre_size >> GRUB_MM_ALIGN_LOG2);

+              h->magic = GRUB_MM_ALLOC_MAGIC;

+              /* region size grows by block size converted back to bytes */

+              r->size += h->size << GRUB_MM_ALIGN_LOG2;

+              /* adjust pre_size to be accurate */

+              r->pre_size &= (GRUB_MM_ALIGN - 1);

+              *p = r;

+              grub_free (h + 1);

+            }

+          /* Replace the old region with the new region */

+          *p = r;

+          return;

+        }

+

+      /*

+       * Is the new region immediately above an existing region? That

+       * is:

+       *   q                       addr

+       *   |<q region>|-q->post_size-|----size-----|

+       */

+      if ((grub_uint8_t *) q + sizeof (*q) + q->size + q->post_size ==

+	  (grub_uint8_t *) addr)

+	{

+	  /*

+	   * Yes! Follow a similar pattern to above, but simpler.

+	   * Our header starts at address - post_size, which should align us

+	   * to a cell boundary.

+	   *

+	   * Cast to (void *) first to avoid the following build error:

+	   *   kern/mm.c: In function ‘grub_mm_init_region’:

+	   *   kern/mm.c:211:15: error: cast increases required alignment of target type [-Werror=cast-align]

+	   *     211 |           h = (grub_mm_header_t) ((grub_uint8_t *) addr - q->post_size);

+	   *         |               ^

+	   * It is safe to do that because proper alignment is enforced in grub_mm_size_sanity_check().

+	   */

+	  h = (grub_mm_header_t)(void *) ((grub_uint8_t *) addr - q->post_size);

+	  /* our size is the allocated size plus post_size, in cells */

+	  h->size = (size + q->post_size) >> GRUB_MM_ALIGN_LOG2;

+	  h->magic = GRUB_MM_ALLOC_MAGIC;

+	  /* region size grows by block size converted back to bytes */

+	  q->size += h->size << GRUB_MM_ALIGN_LOG2;

+	  /* adjust new post_size to be accurate */

+	  q->post_size = (q->post_size + size) & (GRUB_MM_ALIGN - 1);

+	  grub_free (h + 1);

+	  return;

+	}

+    }

   /* Allocate a region from the head.  */

   r = (grub_mm_region_t) ALIGN_UP ((grub_addr_t) addr, GRUB_MM_ALIGN);

@@ -195,6 +230,7 @@ grub_mm_init_region (void *addr, grub_size_t size)

   r->first = h;

   r->pre_size = (grub_addr_t) r - (grub_addr_t) addr;

   r->size = (h->size << GRUB_MM_ALIGN_LOG2);

+  r->post_size = size - r->size;

   /* Find where to insert this region. Put a smaller one before bigger ones,

      to prevent fragmentation.  */

diff --git a/include/grub/mm_private.h b/include/grub/mm_private.h

index a688b92a83..96c2d816be 100644

--- a/include/grub/mm_private.h

+++ b/include/grub/mm_private.h

@@ -81,8 +81,17 @@ typedef struct grub_mm_region

    */

   grub_size_t pre_size;

+  /*

+   * Likewise, the post-size is the number of bytes we wasted at the end

+   * of the allocation because it wasn't a multiple of GRUB_MM_ALIGN

+   */

+  grub_size_t post_size;

+

   /* How many bytes are in this region? (free and allocated) */

   grub_size_t size;

+

+  /* pad to a multiple of cell size */

+  char padding[3 * GRUB_CPU_SIZEOF_VOID_P];

 }

 *grub_mm_region_t;