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Subject[PATCH 4.4 14/35] memblock: do not start bottom-up allocations with kernel_end
Date
From: Roman Gushchin <guro@fb.com>

[ Upstream commit 2dcb3964544177c51853a210b6ad400de78ef17d ]

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:

hugetlb_cma: reserve 2048 MiB, up to 2048 MiB per node
------------[ cut here ]------------
memblock: bottom-up allocation failed, memory hotremove may be affected
WARNING: CPU: 0 PID: 0 at mm/memblock.c:332 memblock_find_in_range_node+0x178/0x25a
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 5.10.0+ #1169
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1.fc33 04/01/2014
RIP: 0010:memblock_find_in_range_node+0x178/0x25a
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
RSP: 0000:ffffffff88803d18 EFLAGS: 00010086 ORIG_RAX: 0000000000000000
RAX: 0000000000000000 RBX: 0000000240000000 RCX: 00000000ffffdfff
RDX: 00000000ffffdfff RSI: 00000000ffffffea RDI: 0000000000000046
RBP: 0000000100000000 R08: ffffffff88922788 R09: 0000000000009ffb
R10: 00000000ffffe000 R11: 3fffffffffffffff R12: 0000000000000000
R13: 0000000000000000 R14: 0000000080000000 R15: 00000001fb42c000
FS: 0000000000000000(0000) GS:ffffffff88f71000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffa080fb401000 CR3: 00000001fa80a000 CR4: 00000000000406b0
Call Trace:
memblock_alloc_range_nid+0x8d/0x11e
cma_declare_contiguous_nid+0x2c4/0x38c
hugetlb_cma_reserve+0xdc/0x128
flush_tlb_one_kernel+0xc/0x20
native_set_fixmap+0x82/0xd0
flat_get_apic_id+0x5/0x10
register_lapic_address+0x8e/0x97
setup_arch+0x8a5/0xc3f
start_kernel+0x66/0x547
load_ucode_bsp+0x4c/0xcd
secondary_startup_64_no_verify+0xb0/0xbb
random: get_random_bytes called from __warn+0xab/0x110 with crng_init=0
---[ 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.

Link: https://lkml.kernel.org/r/20201217201214.3414100-2-guro@fb.com
Fixes: 8fabc623238e ("powerpc: Ensure that swiotlb buffer is allocated from low memory")
Signed-off-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Wonhyuk Yang <vvghjk1234@gmail.com>
Cc: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
mm/memblock.c | 49 ++++++-------------------------------------------
1 file changed, 6 insertions(+), 43 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index f8fab45bfdb75..ff51a37eb86be 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -189,14 +189,6 @@ __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.
- *
* RETURNS:
* Found address on success, 0 on failure.
*/
@@ -204,8 +196,6 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t size,
phys_addr_t align, phys_addr_t start,
phys_addr_t end, int nid, ulong flags)
{
- phys_addr_t kernel_end, ret;
-
/* pump up @end */
if (end == MEMBLOCK_ALLOC_ACCESSIBLE)
end = memblock.current_limit;
@@ -213,40 +203,13 @@ 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(1, "memblock: bottom-up allocation failed, "
- "memory hotunplug 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);
}

/**
--
2.27.0


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