[PATCH v2 2/2] memblock: do not start bottom-up allocations with kernel_end
From: Roman Gushchin
Date: Thu Dec 17 2020 - 15:13:18 EST
With kaslr the kernel image is placed at a random place, so starting
the bottom-up allocation with the kernel_end can result in an
allocation failure and a warning like this one:
[ 0.002920] hugetlb_cma: reserve 2048 MiB, up to 2048 MiB per node
[ 0.002921] ------------[ cut here ]------------
[ 0.002922] memblock: bottom-up allocation failed, memory hotremove may be affected
[ 0.002937] WARNING: CPU: 0 PID: 0 at mm/memblock.c:332 memblock_find_in_range_node+0x178/0x25a
[ 0.002937] Modules linked in:
[ 0.002939] CPU: 0 PID: 0 Comm: swapper Not tainted 5.10.0+ #1169
[ 0.002940] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1.fc33 04/01/2014
[ 0.002942] RIP: 0010:memblock_find_in_range_node+0x178/0x25a
[ 0.002944] Code: e9 6d ff ff ff 48 85 c0 0f 85 da 00 00 00 80 3d 9b 35 df 00 00 75 15 48 c7 c7 c0 75 59 88 c6 05 8b 35 df 00 01 e8 25 8a fa ff <0f> 0b 48 c7 44 24 20 ff ff ff ff 44 89 e6 44 89 ea 48 c7 c1 70 5c
[ 0.002945] RSP: 0000:ffffffff88803d18 EFLAGS: 00010086 ORIG_RAX: 0000000000000000
[ 0.002947] RAX: 0000000000000000 RBX: 0000000240000000 RCX: 00000000ffffdfff
[ 0.002948] RDX: 00000000ffffdfff RSI: 00000000ffffffea RDI: 0000000000000046
[ 0.002948] RBP: 0000000100000000 R08: ffffffff88922788 R09: 0000000000009ffb
[ 0.002949] R10: 00000000ffffe000 R11: 3fffffffffffffff R12: 0000000000000000
[ 0.002950] R13: 0000000000000000 R14: 0000000080000000 R15: 00000001fb42c000
[ 0.002952] FS: 0000000000000000(0000) GS:ffffffff88f71000(0000) knlGS:0000000000000000
[ 0.002953] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.002954] CR2: ffffa080fb401000 CR3: 00000001fa80a000 CR4: 00000000000406b0
[ 0.002956] Call Trace:
[ 0.002961] ? memblock_alloc_range_nid+0x8d/0x11e
[ 0.002963] ? cma_declare_contiguous_nid+0x2c4/0x38c
[ 0.002964] ? hugetlb_cma_reserve+0xdc/0x128
[ 0.002968] ? flush_tlb_one_kernel+0xc/0x20
[ 0.002969] ? native_set_fixmap+0x82/0xd0
[ 0.002971] ? flat_get_apic_id+0x5/0x10
[ 0.002973] ? register_lapic_address+0x8e/0x97
[ 0.002975] ? setup_arch+0x8a5/0xc3f
[ 0.002978] ? start_kernel+0x66/0x547
[ 0.002980] ? load_ucode_bsp+0x4c/0xcd
[ 0.002982] ? secondary_startup_64_no_verify+0xb0/0xbb
[ 0.002986] random: get_random_bytes called from __warn+0xab/0x110 with crng_init=0
[ 0.002988] ---[ end trace f151227d0b39be70 ]---
At the same time, the kernel image is protected with memblock_reserve(),
so we can just start searching at PAGE_SIZE. In this case the
bottom-up allocation has the same chances to success as a top-down
allocation, so there is no reason to fallback in the case of a
failure. All together it simplifies the logic.
Signed-off-by: Roman Gushchin <guro@xxxxxx>
---
mm/memblock.c | 49 ++++++-------------------------------------------
1 file changed, 6 insertions(+), 43 deletions(-)
diff --git a/mm/memblock.c b/mm/memblock.c
index b68ee86788af..10bd7d1ef0f4 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -275,14 +275,6 @@ __memblock_find_range_top_down(phys_addr_t start, phys_addr_t end,
*
* Find @size free area aligned to @align in the specified range and node.
*
- * When allocation direction is bottom-up, the @start should be greater
- * than the end of the kernel image. Otherwise, it will be trimmed. The
- * reason is that we want the bottom-up allocation just near the kernel
- * image so it is highly likely that the allocated memory and the kernel
- * will reside in the same node.
- *
- * If bottom-up allocation failed, will try to allocate memory top-down.
- *
* Return:
* Found address on success, 0 on failure.
*/
@@ -291,8 +283,6 @@ static phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t size,
phys_addr_t end, int nid,
enum memblock_flags flags)
{
- phys_addr_t kernel_end, ret;
-
/* pump up @end */
if (end == MEMBLOCK_ALLOC_ACCESSIBLE ||
end == MEMBLOCK_ALLOC_KASAN)
@@ -301,40 +291,13 @@ static phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t size,
/* avoid allocating the first page */
start = max_t(phys_addr_t, start, PAGE_SIZE);
end = max(start, end);
- kernel_end = __pa_symbol(_end);
-
- /*
- * try bottom-up allocation only when bottom-up mode
- * is set and @end is above the kernel image.
- */
- if (memblock_bottom_up() && end > kernel_end) {
- phys_addr_t bottom_up_start;
-
- /* make sure we will allocate above the kernel */
- bottom_up_start = max(start, kernel_end);
- /* ok, try bottom-up allocation first */
- ret = __memblock_find_range_bottom_up(bottom_up_start, end,
- size, align, nid, flags);
- if (ret)
- return ret;
-
- /*
- * we always limit bottom-up allocation above the kernel,
- * but top-down allocation doesn't have the limit, so
- * retrying top-down allocation may succeed when bottom-up
- * allocation failed.
- *
- * bottom-up allocation is expected to be fail very rarely,
- * so we use WARN_ONCE() here to see the stack trace if
- * fail happens.
- */
- WARN_ONCE(IS_ENABLED(CONFIG_MEMORY_HOTREMOVE),
- "memblock: bottom-up allocation failed, memory hotremove may be affected\n");
- }
-
- return __memblock_find_range_top_down(start, end, size, align, nid,
- flags);
+ if (memblock_bottom_up())
+ return __memblock_find_range_bottom_up(start, end, size, align,
+ nid, flags);
+ else
+ return __memblock_find_range_top_down(start, end, size, align,
+ nid, flags);
}
/**
--
2.26.2