On Tue, 2019-05-14 at 13:43:21 UTC, Michael Ellerman wrote:
> The recent commit to cleanup ifdefs in the hugepage initialisation led
> to crashes when using 4K pages as reported by Sachin:
>
> BUG: Kernel NULL pointer dereference at 0x0000001c
> Faulting instruction address: 0xc000000001d1e58c
> Oops: Kernel access of bad area, sig: 11 [#1]
> LE PAGE_SIZE=4K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
> ...
> CPU: 3 PID: 4635 Comm: futex_wake04 Tainted: G W O
> 5.1.0-next-20190507-autotest #1
> NIP: c000000001d1e58c LR: c000000001d1e54c CTR: 0000000000000000
> REGS: c000000004937890 TRAP: 0300
> MSR: 8000000000009033 <SF,EE,ME,IR,DR,RI,LE> CR: 22424822 XER: 00000000
> CFAR: c00000000183e9e0 DAR: 000000000000001c DSISR: 40000000 IRQMASK: 0
> ...
> NIP kmem_cache_alloc+0xbc/0x5a0
> LR kmem_cache_alloc+0x7c/0x5a0
> Call Trace:
> huge_pte_alloc+0x580/0x950
> hugetlb_fault+0x9a0/0x1250
> handle_mm_fault+0x490/0x4a0
> __do_page_fault+0x77c/0x1f00
> do_page_fault+0x28/0x50
> handle_page_fault+0x18/0x38
>
> This is caused by us trying to allocate from a NULL kmem cache in
> __hugepte_alloc(). The kmem cache is NULL because it was never
> allocated in hugetlbpage_init(), because add_huge_page_size() returned
> an error.
>
> The reason add_huge_page_size() returned an error is a simple typo, we
> are calling check_and_get_huge_psize(size) when we should be passing
> shift instead.
>
> The fact that we're able to trigger this path when the kmem caches are
> NULL is a separate bug, ie. we should not advertise any hugepage sizes
> if we haven't setup the required caches for them.
>
> This was only seen with 4K pages, with 64K pages we don't need to
> allocate any extra kmem caches because the 16M hugepage just occupies
> a single entry at the PMD level.
>
> Fixes: 723f268f19da ("powerpc/mm: cleanup ifdef mess in add_huge_page_size()")
> Reported-by: Sachin Sant <sach...@linux.ibm.com>
> Tested-by: Sachin Sant <sach...@linux.ibm.com>
> Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
> Reviewed-by: Christophe Leroy <christophe.le...@c-s.fr>
> Reviewed-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
Applied to powerpc fixes.
https://git.kernel.org/powerpc/c/7338874c337f01dc84597a5500a58873
cheers
