Messages in this thread | | | Subject | Re: Fwd: [PATCH] x86: Use larger chunks in mtrr_cleanup | From | Toshi Kani <> | Date | Thu, 03 Sep 2015 18:48:46 -0600 |
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On Fri, 2015-09-04 at 01:54 +0200, Luis R. Rodriguez wrote: > On Thu, Sep 03, 2015 at 05:21:14PM -0600, Toshi Kani wrote: > > On Fri, 2015-09-04 at 00:45 +0200, Luis R. Rodriguez wrote: > > > On Thu, Sep 03, 2015 at 04:25:31PM -0600, Toshi Kani wrote: : > > > > On Xen, > > > > > > When Xen is used a platform firmware may still set up MTRR, even if the > > > hypervisor doesn't set up MTRR right ? So same issue and question here. > > > > Right, I meant to say Xen guests. > > Ah but its import complicated than that. > > > In case of the Xen hypervisor, > > mtrr_type_lookup() returns a valid type as it runs on a platform. > > I am not sure if this happens today, I know MTRR is simply disabled by > the Xen Hypervisor on the CPU explicitly, it disable it so guests reading > the MTRR capabilities sees it as disabled when queried.
Oh, I would not let the hypervisor to disable MTRRs...
> Then since the Xen Linux guests cannot speak MTRR through the hypervisor > (for instance Xen guests cannot ask Xen hypervisor to mtrr_type_lookup() for > it) if PCI passthrough is used it could mean a guest might set up / use > incorrect info as well. > > If I undestand this correctly then I think we're in a pickle with Xen unless > we add hypervisor support and hypercall support for mtrr_type_lookup().
I was under assumption that MTRRs are emulated and disabled on guests. Isn't guest physical address virtualized? I know other proprietary VMMs on IA64, but know nothing about Xen... So, please disregard my comments to Xen. :-)
Thanks, -Toshi
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