On 12/15/2010 01:16 PM, Sethi Varun-B16395 wrote:
> -----Original Message----- > From: kvm-ppc-owner@xxxxxxxxxxxxxxx [mailto:kvm-ppc- > owner@xxxxxxxxxxxxxxx] On Behalf Of Avi Kivity > Sent: Tuesday, December 14, 2010 9:18 PM > To: Yoder Stuart-B08248 > Cc: Hollis Blanchard; Alexander Graf; kvm-ppc@xxxxxxxxxxxxxxx > Subject: Re: re-writing on powerpc > > On 12/14/2010 05:45 PM, Yoder Stuart-B08248 wrote: > > > -----Original Message----- > > > From: Avi Kivity [mailto:avi@xxxxxxxxxx] > > > Sent: Tuesday, December 14, 2010 2:49 AM > > > To: Hollis Blanchard > > > Cc: Yoder Stuart-B08248; Alexander Graf; kvm-ppc@xxxxxxxxxxxxxxx > > > Subject: Re: re-writing on powerpc > > > > > > On 12/13/2010 07:17 PM, Hollis Blanchard wrote: > > > >> Rewriting is dangerous if the guest is unaware of it. As soon > > > as > > it > > > >> is made aware of it, it might as well actually do it in the > > > best > > way > > > >> that suits it. > > > > > > > > Can you list some examples of dangerous scenarios? > > > > > > > > > > - guest checksums own kernel pages > > > - clever compiler reuses code for constant pool > > > - guest patches itself (a la linux alternatives), surprised when it > > sees a > > > different instruction > > > - guest jits own kernel code (like Singularity), gets confused when > > > it reads back something it didn't write > > > > One possible solution to hiding rewriting from guest if it must be > > hidden is to mark patched pages as execute only. If a guest reads a > > patched page, the hypervisor can fix up the read. > > > > Yes. Something that is common to all the problems above is "using code > as data". > > However, execute only would only affect the page's mapping, not the page > itself, yes? So if the page has another mapping, this doesn't work. > But KVM would be aware of guest page mappings, so access permissions for any particular mapping can be controlled by KVM.
kvm isn't aware of all guest mappings (only those that were instantiated in shadow tlb/pagetables).
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