[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [Xen-devel] [PATCH] Proper use of VMX execution controls MSR.
The patch conforms to the spec strictly, but I also think the spec is really odd... Seems Keir hasn't checked it in. -- Dexuan >-----Original Message----- >From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx >[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Keir Fraser >Sent: 2007年3月29日 2:02 >To: Li, Xin B; xen-devel@xxxxxxxxxxxxxxxxxxx >Subject: Re: [Xen-devel] [PATCH] Proper use of VMX execution controls MSR. > >On 28/3/07 16:51, "Li, Xin B" <xin.b.li@xxxxxxxxx> wrote: > >> Better use of VMX execution controls MSR. >> >> Signed-off-by: Xin Li<xin.b.li@xxxxxxxxx> > >Is this actually to fix a problem with a future processor? > >This whole bit-forcing thing seems extremely odd to me. We set the controls >that Xen currently needs to do its job as a VMM properly -- we can't just >clear some of those controls because the processor says to do so. So I think >our current treatment of the MSR high bits is appropriate (if it tells us to >zero one of the control bits that we make use of, we are in trouble -- we >have a processor that isn't backwards compatible!). > >I also feel uneasy about setting extra bits (as specified by the MSR low >bits), but I reason that if we are told to set bits of flags which are >currently architecturally-undefined then it is reasonable to let the >processor tell us what to do with them. Which is why I do respect the MSR >low bits. > >Why did Intel ever choose this insane scheme? Would it have been so hard to >have defined bitmaps with set-to-enable semantics, and always require zero >for reserved bits? Actually I suppose you do have set-to-enable semantics >(otherwise my current asymmetric treatment of MSR high and low words would >not make sense). But all this messing with setting vs. clearing reserved >bits seems pretty stupid. > > -- Keir > > > >_______________________________________________ >Xen-devel mailing list >Xen-devel@xxxxxxxxxxxxxxxxxxx >http://lists.xensource.com/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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