Re: [PATCH] mm/debug_vm_pgtable: Fix kernel crash with page table validate
From: Anshuman Khandual <hidden>
Date: 2020-06-08 11:01:56
Also in:
linux-mm
Hi Aneesh, On 06/08/2020 11:57 AM, Aneesh Kumar K.V wrote:
Architectures can have CONFIG_TRANSPARENT_HUGEPAGE enabled but no THP support enabled based on platforms. For ex: with 4K PAGE_SIZE ppc64 supports THP only with radix translation.
Good catch, never hit this before.
This results in below crash when running with hash translation and
4K PAGE_SIZE.
kernel BUG at arch/powerpc/include/asm/book3s/64/hash-4k.h:140!
cpu 0x61: Vector: 700 (Program Check) at [c000000ff948f860]
pc: c0000000018810f8: debug_vm_pgtable+0x480/0x8b0
lr: c0000000018810ec: debug_vm_pgtable+0x474/0x8b0
...
[c000000ff948faf0] c000000001880fec debug_vm_pgtable+0x374/0x8b0 (unreliable)
[c000000ff948fbf0] c000000000011648 do_one_initcall+0x98/0x4f0
[c000000ff948fcd0] c000000001843928 kernel_init_freeable+0x330/0x3fc
[c000000ff948fdb0] c0000000000122ac kernel_init+0x24/0x148
[c000000ff948fe20] c00000000000cc44 ret_from_kernel_thread+0x5c/0x78
Check for THP support correctlyMakes sense, is this the only configuration which hit the problem ?
quoted hunk ↗ jump to hunk
Cc: anshuman.khandual@arm.com Fixes: 399145f9eb6c ("mm/debug: add tests validating architecture page table helpers") Signed-off-by: Aneesh Kumar K.V <redacted> --- mm/debug_vm_pgtable.c | 3 +++ 1 file changed, 3 insertions(+)diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c index 188c18908964..e60151c5e997 100644 --- a/mm/debug_vm_pgtable.c +++ b/mm/debug_vm_pgtable.c@@ -61,6 +61,9 @@ static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot) { pmd_t pmd = pfn_pmd(pfn, prot); + if (!has_transparent_hugepage()) + return; +
We should also add this check to pud_basic_tests() as well.
WARN_ON(!pmd_same(pmd, pmd)); WARN_ON(!pmd_young(pmd_mkyoung(pmd_mkold(pmd)))); WARN_ON(!pmd_dirty(pmd_mkdirty(pmd_mkclean(pmd))));
The subject line here should mention about correct THP support
detection which fixes the problem. Probably something like this
or similar ("Fix kernel crash with correct THP support check").
- Anshuman