From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH] VTd/dmar: Tweak how the DMAR table is clobbered Date: Fri, 10 Apr 2015 10:08:11 +0100 Message-ID: <552792FB.7020908@citrix.com> References: <1428522270-17363-1-git-send-email-andrew.cooper3@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: "Tian, Kevin" , Xen-devel Cc: "Zhang, Yang Z" List-Id: xen-devel@lists.xenproject.org On 10/04/15 02:23, Tian, Kevin wrote: >> From: Andrew Cooper [mailto:andrew.cooper3@citrix.com] >> Sent: Thursday, April 09, 2015 3:45 AM >> >> Intead of clobbering DMAR -> XMAR and back, clobber to RMAD instead. >> This >> means that changing the signature does not alter the checksum, which allows >> the clobbering/unclobbering to be peformed atomically and idempotently, >> which >> is an advantage on the kexec path which can reenter acpi_dmar_reinstate(). >> >> Signed-off-by: Andrew Cooper >> CC: Yang Zhang >> CC: Kevin Tian > Acked-by: Kevin Tian > > and curious do you observe a real atomic issue in kexec or just catch this > potential issue when reading code? :-) I have run over it once in the past, but mainly it is one small thing on a very long list of tweaks to make the crash path for reliable. As indicated in the other thread, I think the best direction moving forwards is to see about positively preventing dom0 having access, rather than simply hiding the table, but that is a job for another time. ~Andrew