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;