From: Michael Ellerman <patch-notifications@ellerman.id.au>
To: Nicholas Piggin <npiggin@gmail.com>, linuxppc-dev@lists.ozlabs.org
Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH 1/2] powerpc/64s: Fix THP PMD collapse serialisation
Date: Wed, 12 Jun 2019 14:59:11 +1000 (AEST) [thread overview]
Message-ID: <45NvmH6CQKz9sDB@ozlabs.org> (raw)
In-Reply-To: <20190607035636.5446-1-npiggin@gmail.com>
On Fri, 2019-06-07 at 03:56:35 UTC, Nicholas Piggin wrote:
> Commit 1b2443a547f9 ("powerpc/book3s64: Avoid multiple endian conversion
> in pte helpers") changed the actual bitwise tests in pte_access_permitted
> by using pte_write() and pte_present() helpers rather than raw bitwise
> testing _PAGE_WRITE and _PAGE_PRESENT bits.
>
> The pte_present change now returns true for ptes which are !_PAGE_PRESENT
> and _PAGE_INVALID, which is the combination used by pmdp_invalidate to
> synchronize access from lock-free lookups. pte_access_permitted is used by
> pmd_access_permitted, so allowing GUP lock free access to proceed with
> such PTEs breaks this synchronisation.
>
> This bug has been observed on HPT host, with random crashes and corruption
> in guests, usually together with bad PMD messages in the host.
>
> Fix this by adding an explicit check in pmd_access_permitted, and
> documenting the condition explicitly.
>
> The pte_write() change should be okay, and would prevent GUP from falling
> back to the slow path when encountering savedwrite ptes, which matches
> what x86 (that does not implement savedwrite) does.
>
> Fixes: 1b2443a547f9 ("powerpc/book3s64: Avoid multiple endian conversion in pte helpers")
> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> Cc: Christophe Leroy <christophe.leroy@c-s.fr>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Applied to powerpc fixes, thanks.
https://git.kernel.org/powerpc/c/33258a1db165cf43a9e6382587ad06e9
cheers
prev parent reply other threads:[~2019-06-12 5:04 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-07 3:56 [PATCH 1/2] powerpc/64s: Fix THP PMD collapse serialisation Nicholas Piggin
2019-06-07 3:56 ` [PATCH 2/2] powerpc/64s: __find_linux_pte synchronization vs pmdp_invalidate Nicholas Piggin
2019-06-07 5:35 ` Christophe Leroy
2019-06-07 6:31 ` Nicholas Piggin
2019-06-07 5:35 ` Aneesh Kumar K.V
2019-06-12 4:59 ` Michael Ellerman
2019-06-07 5:34 ` [PATCH 1/2] powerpc/64s: Fix THP PMD collapse serialisation Christophe Leroy
2019-06-07 6:40 ` Nicholas Piggin
2019-06-07 5:35 ` Aneesh Kumar K.V
2019-06-12 4:59 ` Michael Ellerman [this message]
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