From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [RFC] Hypercalls from HVM guests Date: Fri, 07 Apr 2006 15:22:27 -0500 Message-ID: <4436CA03.7050509@us.ibm.com> References: <907625E08839C4409CE5768403633E0BA7FBCF@sefsexmb1.amd.com> <4436BDE2.5090504@virtualiron.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4436BDE2.5090504@virtualiron.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Steve Ofsthun Cc: xen-devel@lists.xensource.com, Mats@us.ibm.com, Petersson@linux.ibm.com List-Id: xen-devel@lists.xenproject.org Steve Ofsthun wrote: > Petersson, Mats wrote: > > > This sounds like a simple to use method for communicating with the HVM > code, > but I would like to gracefully detect native execution and print a useful > error message at module load time. Recovering from a native mode > exception > will be very O/S specific (if allowed at all). PIO is probably a bit safer. PIO probing, while a bit ugly, is certainly frequently used. Plus, PIO instructions are not sensitive (whereas CPUID is) which means that it can also be used as a mechanism for non-HVM guests. Regards, Anthony Liguori >> Actually, maybe using an unused index for CPUID (e.g. 0xb0000000) would >> be better? As that's defined to return all zero's, and not cause any >> traps whatever value you use (unless the CPU is so old that it doesn't >> support CPUID, of course). > > This sounds encouraging, but is CPUID always trapped by the HVM code? > > Steve