Messages in this thread | | | Date | Tue, 28 Sep 2010 11:58:05 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH 12/12] xen/mtrr: Add mtrr_if support for Xen mtrr |
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On 09/28/2010 11:46 AM, H. Peter Anvin wrote: > Well, we're specifically talking about a virtual machine which has > direct access to hardware, so it is concerned about the real physical > memory properties of real physical pages. If we can assume that > BIOS/Xen will always set up MTRR correctly then there shouldn't be any > need for the kernel to modify the MTRR itself. How true is that in > general? I don't know, but if we could rely on BIOS then there'd never > be a need to touch MTRR, would there? > Well, in the past MTRRs were abused for device properties mainly by the > X server, but other than that, no, not really. The other thing we do is > the MTRR cleanup (which doesn't involve /proc/mtrr) to deal with > brokenness in the BIOS setup, but that really belongs in the hypervisor > in your case since it fundamentally affects how memory is handled.
Yeah, the hypervisor should definitely deal with that. I have no problem in principle with leaving MTRRs entirely to Xen, but I was just concerned about possible repercussions. Certainly when I first did this work, I was using Fedora 8 whose X server did depend on /proc/mtrr for good performance.
J
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