linux-kernel - Re: [BUG] bug when enabling VM DEBUG

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <AANLkTilhIvv-knAVyivbo3o9LphUO4-j8-iVunlF2qcS@mail.gmail.com>
Date:	Wed, 12 May 2010 17:22:35 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Jamie Lokier <jamie@...reable.org>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>,
	Jeff Garzik <jeff@...zik.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"DE/ATA development list" <linux-ide@...r.kernel.org>,
	saeed bishara <saeed.bishara@...il.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [BUG] bug when enabling VM DEBUG

On Wed, May 12, 2010 at 7:06 AM, Jamie Lokier <jamie@...reable.org> wrote:
> Catalin Marinas wrote:
>> On Wed, 2010-05-12 at 12:53 +0100, Sebastian Andrzej Siewior wrote:
>> > * Catalin Marinas | 2010-05-12 12:10:39 [+0100]:
>> >
>> > >> > --- a/drivers/ata/libata-sff.c
>> > >> > +++ b/drivers/ata/libata-sff.c
>> > >> > @@ -894,7 +894,7 @@ static void ata_pio_sector(struct ata_queued_cmd *qc)
>> > >> >                                         do_write);
>> > >> >          }
>> > >> >
>> > >> > -       if (!do_write)
>> > >> > +       if (!do_write&&  !PageSlab(page))
>> > >> >                  flush_dcache_page(page);
>> > >>
>> > >> I would think that check belongs inside flush_dcache_page itself, rather
>> > >> than forcing every driver to include it..
>> > >
>> > >Sebastian (cc'ed) reported this as well for MIPS.
>> > Thx. The patch above looks what I've sent a while ago. Jeff was going to
>> > merge it afaik.
>> >
>> > >I think it makes sense for this check to be done in the
>> > >flush_dcache_page() function.
>> >
>> > Why should flush_dcache_page() not flush pages you tell it?
>> > From Documentation/cachetlb.txt:
>> > |   NOTE: This routine need only be called for page cache pages
>> > |          which can potentially ever be mapped into the address
>> > |          space of a user process.  So for example, VFS layer code
>> > |          handling vfs symlinks in the page cache need not call
>> > |          this interface at all.
>> >
>> > A page from slab or stack is not going to see the sky of user land and
>> > therefore it should not be fed into flush_dcache_page().
>>
>> You are right :), so fixing the driver is the best approach.
>
> It worries me that a driver has any knowledge of the PageSlab() flag,
> though.  Especially uncommented knowledge.  That flag seems VM
> internal, and it's conceptually iffy: Kernel code using
> get_free_pages() and using that for I/O also does not see the sky of
> user land.
>
> If all the PIO drivers have to be changed, I'd be happier with:
>
>    flush_dcache_page_for_pio()
>
> which wraps the check, explains it, and provides a single place to
> change if needed.

Indeed.. It's obscure enough for drivers to need to worry about these
details of cache flushing/invalidation at all, let alone for them to
have to worry about even more obscure details..
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/