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From: Michael Ellerman <mpe@ellerman.id.au>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
	Nicholas Piggin <npiggin@gmail.com>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc/64e: Fix wrong test in __ptep_test_and_clear_young()
Date: Tue, 05 Sep 2023 12:36:36 +1000	[thread overview]
Message-ID: <87a5u1ibwr.fsf@mail.lhotse> (raw)
In-Reply-To: <2daed51109cbd7e7fbd26fab4e77fc6a27dee63e.1693643773.git.christophe.leroy@csgroup.eu>

Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> Commit 45201c879469 ("powerpc/nohash: Remove hash related code from
> nohash headers.") replaced:
>
>   if ((pte_val(*ptep) & (_PAGE_ACCESSED | _PAGE_HASHPTE)) == 0)
> 	return 0;
>
> By:
>
>   if (pte_young(*ptep))
> 	return 0;
>
> But it should be:
>
>   if (!pte_young(*ptep))
> 	return 0;


That seems bad :)

But I don't know off the top of my head where
__ptep_test_and_clear_young() is used, and so what the symptoms could
be. Presumably nothing too bad or someone would have noticed?

cheers

WARNING: multiple messages have this Message-ID (diff)
From: Michael Ellerman <mpe@ellerman.id.au>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
	Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>,
	linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc/64e: Fix wrong test in __ptep_test_and_clear_young()
Date: Tue, 05 Sep 2023 12:36:36 +1000	[thread overview]
Message-ID: <87a5u1ibwr.fsf@mail.lhotse> (raw)
In-Reply-To: <2daed51109cbd7e7fbd26fab4e77fc6a27dee63e.1693643773.git.christophe.leroy@csgroup.eu>

Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> Commit 45201c879469 ("powerpc/nohash: Remove hash related code from
> nohash headers.") replaced:
>
>   if ((pte_val(*ptep) & (_PAGE_ACCESSED | _PAGE_HASHPTE)) == 0)
> 	return 0;
>
> By:
>
>   if (pte_young(*ptep))
> 	return 0;
>
> But it should be:
>
>   if (!pte_young(*ptep))
> 	return 0;


That seems bad :)

But I don't know off the top of my head where
__ptep_test_and_clear_young() is used, and so what the symptoms could
be. Presumably nothing too bad or someone would have noticed?

cheers

  reply	other threads:[~2023-09-05  2:37 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-02  8:36 [PATCH] powerpc/64e: Fix wrong test in __ptep_test_and_clear_young() Christophe Leroy
2023-09-02  8:36 ` Christophe Leroy
2023-09-05  2:36 ` Michael Ellerman [this message]
2023-09-05  2:36   ` Michael Ellerman
2023-09-05  4:46   ` Christophe Leroy
2023-09-05  4:46     ` Christophe Leroy
2023-09-05  7:03     ` Christophe Leroy
2023-09-05  7:03       ` Christophe Leroy

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