From: Christophe LEROY <christophe.leroy@c-s.fr>
To: Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>, Scott Wood <oss@buserror.net>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 2/5] powerpc/mm: split store_updates_sp() in two parts in do_page_fault()
Date: Fri, 2 Jun 2017 11:39:23 +0200 [thread overview]
Message-ID: <6daf8f4e-9b39-d585-2c64-9b0348fef123@c-s.fr> (raw)
In-Reply-To: <871sr23flh.fsf@concordia.ellerman.id.au>
Le 02/06/2017 à 11:26, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@c-s.fr> writes:
>
>> Only the get_user() in store_updates_sp() has to be done outside
>> the mm semaphore. All the comparison can be done within the semaphore,
>> so only when really needed.
>>
>> As we got a DSI exception, the address pointed by regs->nip is
>> obviously valid, otherwise we would have had a instruction exception.
>> So __get_user() can be used instead of get_user()
>
> I don't think that part is true.
>
> You took a DSI so there *was* an instruction at NIP, but since then it
> may have been unmapped by another thread.
>
> So I don't think you can assume the get_user() will succeed.
>
The difference between get_user() and __get_user() is that get_user()
performs an access_ok() in addition.
Doesn't access_ok() only checks whether addr is below TASK_SIZE to
ensure it is a valid user address ?
Christophe
next prev parent reply other threads:[~2017-06-02 9:39 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-19 12:56 [PATCH 0/5] powerpc/mm: some cleanup of do_page_fault() Christophe Leroy
2017-04-19 12:56 ` [PATCH 1/5] powerpc/mm: only call store_updates_sp() on stores in do_page_fault() Christophe Leroy
2017-04-24 9:10 ` Aneesh Kumar K.V
2017-06-05 10:21 ` [1/5] " Michael Ellerman
2017-04-19 12:56 ` [PATCH 2/5] powerpc/mm: split store_updates_sp() in two parts " Christophe Leroy
2017-04-24 9:11 ` Aneesh Kumar K.V
2017-06-02 9:26 ` Michael Ellerman
2017-06-02 9:39 ` Christophe LEROY [this message]
2017-06-02 12:11 ` Benjamin Herrenschmidt
2017-06-02 12:31 ` Christophe LEROY
2017-06-05 10:49 ` Michael Ellerman
2017-06-05 10:49 ` Michael Ellerman
2017-06-05 10:45 ` Michael Ellerman
2017-06-05 10:45 ` Michael Ellerman
2017-06-05 17:48 ` christophe leroy
2017-06-06 11:00 ` Michael Ellerman
2017-06-06 11:00 ` Michael Ellerman
2017-06-06 13:29 ` Christophe LEROY
2017-04-19 12:56 ` [PATCH 3/5] powerpc/mm: remove a redundant test " Christophe Leroy
2017-04-19 12:56 ` [PATCH 4/5] powerpc/mm: Evaluate user_mode(regs) only once " Christophe Leroy
2017-04-24 9:13 ` Aneesh Kumar K.V
2017-04-19 12:56 ` [PATCH 5/5] powerpc/mm: The 8xx doesn't call do_page_fault() for breakpoints Christophe Leroy
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