lkml.org 
[lkml]   [2021]   [Dec]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v3] arm64/mm: avoid fixmap race condition when create pud mapping
From
On 16.12.21 09:28, Jianyong Wu wrote:
> The 'fixmap' is a global resource and is used recursively by
> create pud mapping(), leading to a potential race condition in the
> presence of a concurrent call to alloc_init_pud():
>
> kernel_init thread virtio-mem workqueue thread
> ================== ===========================
>
> alloc_init_pud(...) alloc_init_pud(...)
> pudp = pud_set_fixmap_offset(...) pudp = pud_set_fixmap_offset(...)
> READ_ONCE(*pudp)
> pud_clear_fixmap(...)
> READ_ONCE(*pudp) // CRASH!
>
> As kernel may sleep during creating pud mapping, introduce a mutex lock to
> serialise use of the fixmap entries by alloc_init_pud().
>
> Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
> ---
>
> Change log:
>
> from v2 to v3:
> change spin lock to mutex lock as kernel may sleep when create pud
> map.
>
> arch/arm64/mm/mmu.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index acfae9b41cc8..e680a6a8ca40 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -63,6 +63,7 @@ static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss __maybe_unused;
> static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss __maybe_unused;
>
> static DEFINE_SPINLOCK(swapper_pgdir_lock);
> +static DEFINE_MUTEX(fixmap_lock);
>
> void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)
> {
> @@ -329,6 +330,11 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
> }
> BUG_ON(p4d_bad(p4d));
>
> + /*
> + * We only have one fixmap entry per page-table level, so take
> + * the fixmap lock until we're done.
> + */
> + mutex_lock(&fixmap_lock);
> pudp = pud_set_fixmap_offset(p4dp, addr);
> do {
> pud_t old_pud = READ_ONCE(*pudp);
> @@ -359,6 +365,7 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
> } while (pudp++, addr = next, addr != end);
>
> pud_clear_fixmap();
> + mutex_unlock(&fixmap_lock);
> }
>
> static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
>

Hopefully now we get it right and there are not any "special" callpaths :)

Acked-by: David Hildenbrand <david@redhat.com>

--
Thanks,

David / dhildenb

\
 
 \ /
  Last update: 2021-12-16 16:20    [W:0.099 / U:4.516 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site