From: David Hildenbrand <david@redhat.com>
To: Jianyong Wu <jianyong.wu@arm.com>,
catalin.marinas@arm.com, will@kernel.org,
anshuman.khandual@arm.com, akpm@linux-foundation.org
Cc: quic_qiancai@quicinc.com, ardb@kernel.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, gshan@redhat.com,
justin.he@arm.com, nd@arm.com
Subject: Re: [PATCH v3] arm64/mm: avoid fixmap race condition when create pud mapping
Date: Thu, 16 Dec 2021 16:19:30 +0100 [thread overview]
Message-ID: <995f4a1c-35e2-03ef-d09d-14e822e186fe@redhat.com> (raw)
In-Reply-To: <20211216082812.165387-1-jianyong.wu@arm.com>
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
next prev parent reply other threads:[~2021-12-16 15:19 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-16 8:28 [PATCH v3] arm64/mm: avoid fixmap race condition when create pud mapping Jianyong Wu
2021-12-16 15:19 ` David Hildenbrand [this message]
2021-12-17 9:30 ` Mark Rutland
2021-12-17 10:09 ` Jianyong Wu
2022-01-05 18:03 ` Catalin Marinas
2022-01-06 10:13 ` Jianyong Wu
2022-01-06 15:56 ` Catalin Marinas
2022-01-07 9:10 ` Jianyong Wu
2022-01-07 10:42 ` Catalin Marinas
2022-01-26 4:20 ` Justin He
2022-01-26 8:36 ` Ard Biesheuvel
2022-01-26 10:09 ` Jianyong Wu
2022-01-26 10:12 ` Ard Biesheuvel
2022-01-26 10:17 ` David Hildenbrand
2022-01-26 10:28 ` Jianyong Wu
2022-01-26 10:30 ` David Hildenbrand
2022-01-26 10:31 ` David Hildenbrand
2022-01-27 6:24 ` Jianyong Wu
2022-01-27 12:22 ` David Hildenbrand
2022-01-27 12:34 ` Catalin Marinas
2022-01-31 8:13 ` Jianyong Wu
2022-01-31 8:10 ` Jianyong Wu
2022-01-27 1:31 ` Justin He
2022-01-07 10:53 ` Catalin Marinas
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