[Re: runtime regression with "x86/mm/pat: Emulate PAT when it is disabled"] On 10/03/2016 (Thu 18:20) Borislav Petkov wrote:
> On Thu, Mar 10, 2016 at 09:49:51AM -0700, Toshi Kani wrote: > > This confirms the issue - QEMU's virtual Intel CPU does not support MTRR. > > > > When MTRR is disabled, the kernel does not call pat_init(). pat_enabled() > > is still set to true when CONFIG_X86_PAT is set. CONFIG_X86_PAT depends on > > CONFIG_MTRR, and assumes that MTRR is enabled. > > Aha, so "qemu32" model doesn't support MTRRs but "kvm32" does, for > example. And so do the majority of the other CPU types. So, I guess that is a qemu bug? If there is no real silicon out there that has no MTRR but does claim PAT, then qemu32 is a flawed CPU type? > > Paul, can you guys run with something else besides "qemu32"? You can > even take a 64-bit one and run a 32-bit guest on it. That is probably more of an RP question. In principle I guess other CPU types are on the table, and most likely qemu32 is just there from historical reasons. We do know that we don't want "-cpu host" though, since that will introduce variability into the automated testing. Paul. -- > > :-) > > -- > Regards/Gruss, > Boris. > > SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB > 21284 (AG Nürnberg) > --
