From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: New 745x errata From: Adrian Cox To: Tom Rini Cc: linuxppc-dev@lists.linuxppc.org In-Reply-To: <20031117150409.GA30251@ip68-0-152-218.tc.ph.cox.net> References: <1068721518.23764.84.camel@newt> <20031114162414.GD13003@ip68-0-152-218.tc.ph.cox.net> <1069081074.10537.16.camel@newt> <20031117150409.GA30251@ip68-0-152-218.tc.ph.cox.net> Content-Type: text/plain Date: 17 Nov 2003 15:34:05 +0000 Message-Id: <1069083245.10537.58.camel@newt> Mime-Version: 1.0 Sender: owner-linuxppc-dev@lists.linuxppc.org List-Id: On Mon, 2003-11-17 at 15:04, Tom Rini wrote: > On Mon, Nov 17, 2003 at 02:57:53PM +0000, Adrian Cox wrote: > > Any opinion on the dcbt issue? It looks like it could provide a way for > > a malicious userspace application to crash the machine, though it needs > > a combination of: > > 1) good timing > > 2) a peripheral that would be confused by an extra read cycle > It depends on what the fix is. For example, Linus just fixed a > theoretical race that has a 1-3 cycle (depending on x86 cpu I think he > said) race because he happened to be in there anyhow (and it turns out > the fix is easy). The fix is simple, but carries a performance cost: set the HID0_NOPTI bit and disable all dcbt instructions. The kernel uses dcbt instructions in a lot of places, but copy_page is what matters the most. A copy_page routine using dst instructions might be faster anyway, and would be immune to this problem. On closer reading, I now think this problem may be harmless - see my explanation to Gabriel Paubert for more details. - Adrian Cox http://www.humboldt.co.uk/ ** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/