linux-kernel - Re: USB mass storage and ARM cache coherency

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]

Date:	Thu, 04 Mar 2010 22:11:51 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Paul Mundt <lethal@...ux-sh.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Pavel Machek <pavel@....cz>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux@....linux.org.uk, mdharm-kernel@...-eyed-alien.net,
	linux-usb@...r.kernel.org, x0082077@...com,
	sshtylyov@...mvista.com, tom.leiming@...il.com,
	bigeasy@...utronix.de, oliver@...kum.org,
	linux-kernel@...r.kernel.org, santosh.shilimkar@...com,
	greg@...ah.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: USB mass storage and ARM cache coherency

On Thu, 2010-03-04 at 21:37 +0000, Benjamin Herrenschmidt wrote:
> On Thu, 2010-03-04 at 18:07 +0000, Catalin Marinas wrote:
> > I'm not familiar with SH but for PIO devices the flushing shouldn't be
> > more aggressive. For the DMA devices, Russell suggested that we mark
> > the page as clean (set PG_dcache_clean) in the DMA API to avoid the
> > default flushing.
> 
> I really like that idea, as I said earlier, but I'm worried about the I$
> side of things. IE. What I'm trying to say is that I can't see how to do
> that optimisation without ending up with missing I$ invalidations or
> doing way too many of them, unless we have a separate bit to track I$
> state.

But does this optimisation really matter? I think with careful checking
in set_pte_at(), you are not going to invalidate the I-cache more than
necessary. If the original page wasn't pte_present() you would need to
do the I-cache invalidation. The other cases where set_pte_at() is
called for LRU (pte_young) or COW (pte_write) we can avoid the extra
invalidation.

-- 
Catalin

--
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/