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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 |
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From: Zhang Boyang <zhangboyang.id@gmail.com> |
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Date: Sun, 29 Jan 2023 19:49:31 +0800 |
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Subject: [PATCH] mm: Adjust new region size to take management overhead into |
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account |
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When grub_memalign() encounters out-of-memory, it will try |
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grub_mm_add_region_fn() to request more memory from system firmware. |
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However, the size passed to it doesn't take region management overhead |
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into account. Adding a memory area of "size" bytes may result in a heap |
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region of less than "size" bytes really available. Thus, the new region |
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may not be adequate for current allocation request, confusing |
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out-of-memory handling code. |
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This patch introduces GRUB_MM_MGMT_OVERHEAD to address the region |
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management overhead (e.g. metadata, padding). The value of this new |
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constant must be large enough to make sure grub_memalign(align, size) |
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always succeeds after a successful call to |
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grub_mm_init_region(addr, size + align + GRUB_MM_MGMT_OVERHEAD), |
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for any given addr and size (assuming no integer overflow). |
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The size passed to grub_mm_add_region_fn() is now correctly adjusted, |
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thus if grub_mm_add_region_fn() succeeded, current allocation request |
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can always succeed. |
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Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com> |
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com> |
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(cherry picked from commit 2282cbfe5aa1ff6c1bbcbdcd2003089ad7c03ba3) |
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--- |
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grub-core/kern/mm.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++--- |
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1 file changed, 61 insertions(+), 3 deletions(-) |
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diff --git a/grub-core/kern/mm.c b/grub-core/kern/mm.c |
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index da1ac9427c..f29a3e5cbd 100644 |
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--- a/grub-core/kern/mm.c |
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+++ b/grub-core/kern/mm.c |
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@@ -83,6 +83,46 @@ |
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+/* |
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+ * GRUB_MM_MGMT_OVERHEAD is an upper bound of management overhead of |
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+ * each region, with any possible padding taken into account. |
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+ * |
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+ * The value must be large enough to make sure grub_memalign(align, size) |
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+ * always succeeds after a successful call to |
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+ * grub_mm_init_region(addr, size + align + GRUB_MM_MGMT_OVERHEAD), |
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+ * for any given addr, align and size (assuming no interger overflow). |
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+ * |
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+ * The worst case which has maximum overhead is shown in the figure below: |
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+ * |
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+ * +-- addr |
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+ * v |<- size + align ->| |
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+ * +---------+----------------+----------------+------------------+---------+ |
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+ * | padding | grub_mm_region | grub_mm_header | usable bytes | padding | |
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+ * +---------+----------------+----------------+------------------+---------+ |
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+ * |<- a ->|<- b ->|<- c ->|<- d ->|<- e ->| |
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+ * ^ |
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+ * b == sizeof (struct grub_mm_region) | / Assuming no other suitable |
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+ * c == sizeof (struct grub_mm_header) | | block is available, then: |
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+ * d == size + align +-| If align == 0, this will be |
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+ * | the pointer returned by next |
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+ * Assuming addr % GRUB_MM_ALIGN == 1, then: | grub_memalign(align, size). |
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+ * a == GRUB_MM_ALIGN - 1 | If align > 0, this chunk may |
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+ * | need to be split to fulfill |
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+ * Assuming d % GRUB_MM_ALIGN == 1, then: | alignment requirements, and |
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+ * e == GRUB_MM_ALIGN - 1 | the returned pointer may be |
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+ * \ inside these usable bytes. |
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+ * Therefore, the maximum overhead is: |
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+ * a + b + c + e == (GRUB_MM_ALIGN - 1) + sizeof (struct grub_mm_region) |
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+ * + sizeof (struct grub_mm_header) + (GRUB_MM_ALIGN - 1) |
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+ */ |
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+#define GRUB_MM_MGMT_OVERHEAD ((GRUB_MM_ALIGN - 1) \ |
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+ + sizeof (struct grub_mm_region) \ |
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+ + sizeof (struct grub_mm_header) \ |
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+ + (GRUB_MM_ALIGN - 1)) |
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+ |
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+/* The size passed to grub_mm_add_region_fn() is aligned up by this value. */ |
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+#define GRUB_MM_HEAP_GROW_ALIGN 4096 |
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+ |
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grub_mm_region_t grub_mm_base; |
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grub_mm_add_region_func_t grub_mm_add_region_fn; |
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@@ -230,6 +270,11 @@ grub_mm_init_region (void *addr, grub_size_t size) |
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grub_dprintf ("regions", "No: considering a new region at %p of size %" PRIxGRUB_SIZE "\n", |
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addr, size); |
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+ /* |
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+ * If you want to modify the code below, please also take a look at |
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+ * GRUB_MM_MGMT_OVERHEAD and make sure it is synchronized with the code. |
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+ */ |
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+ |
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/* Allocate a region from the head. */ |
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r = (grub_mm_region_t) ALIGN_UP ((grub_addr_t) addr, GRUB_MM_ALIGN); |
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@@ -410,6 +455,7 @@ grub_memalign (grub_size_t align, grub_size_t size) |
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{ |
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grub_mm_region_t r; |
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grub_size_t n = ((size + GRUB_MM_ALIGN - 1) >> GRUB_MM_ALIGN_LOG2) + 1; |
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+ grub_size_t grow; |
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int count = 0; |
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if (!grub_mm_base) |
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@@ -418,10 +464,22 @@ grub_memalign (grub_size_t align, grub_size_t size) |
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if (size > ~(grub_size_t) align) |
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goto fail; |
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+ /* |
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+ * Pre-calculate the necessary size of heap growth (if applicable), |
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+ * with region management overhead taken into account. |
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+ */ |
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+ if (grub_add (size + align, GRUB_MM_MGMT_OVERHEAD, &grow)) |
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+ goto fail; |
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+ |
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+ /* Align up heap growth to make it friendly to CPU/MMU. */ |
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+ if (grow > ~(grub_size_t) (GRUB_MM_HEAP_GROW_ALIGN - 1)) |
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+ goto fail; |
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+ grow = ALIGN_UP (grow, GRUB_MM_HEAP_GROW_ALIGN); |
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+ |
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/* We currently assume at least a 32-bit grub_size_t, |
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so limiting allocations to <adress space size> - 1MiB |
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in name of sanity is beneficial. */ |
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- if ((size + align) > ~(grub_size_t) 0x100000) |
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+ if (grow > ~(grub_size_t) 0x100000) |
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goto fail; |
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align = (align >> GRUB_MM_ALIGN_LOG2); |
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@@ -447,7 +505,7 @@ grub_memalign (grub_size_t align, grub_size_t size) |
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count++; |
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if (grub_mm_add_region_fn != NULL && |
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- grub_mm_add_region_fn (size, GRUB_MM_ADD_REGION_CONSECUTIVE) == GRUB_ERR_NONE) |
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+ grub_mm_add_region_fn (grow, GRUB_MM_ADD_REGION_CONSECUTIVE) == GRUB_ERR_NONE) |
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goto again; |
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/* fallthrough */ |
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@@ -462,7 +520,7 @@ grub_memalign (grub_size_t align, grub_size_t size) |
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* Try again even if this fails, in case it was able to partially |
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* satisfy the request |
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*/ |
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- grub_mm_add_region_fn (size, GRUB_MM_ADD_REGION_NONE); |
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+ grub_mm_add_region_fn (grow, GRUB_MM_ADD_REGION_NONE); |
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goto again; |
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} |
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