Re: 1GB hugepages and intel_xc_cpuid_policy by default disables it.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Mon, Nov 10, 2014 at 05:08:09AM +0000, Zhang, Yang Z wrote:
> Konrad Rzeszutek Wilk wrote on 2014-01-16:
> > On Mon, Jan 13, 2014 at 11:51:28AM +0000, Jan Beulich wrote:
> >>>>> On 13.01.14 at 12:38, Ian Campbell <Ian.Campbell@citrix.com> wrote:
> >>> On Mon, 2014-01-13 at 11:30 +0000, Jan Beulich wrote:
> >>>> In fact I can't see where this would be forced off:
> >>>> xc_cpuid_x86.c only does so in the PV case, and all
> >>>> hvm_pse1gb_supported() is that the CPU supports it and the domain uses HAP.
> >>> 
> >>> Took me a while to spot it too:
> >>> static void intel_xc_cpuid_policy( [...]
> >>>             case 0x80000001: {
> >>>                 int is_64bit = hypervisor_is_64bit(xch) && is_pae;
> >>>                 
> >>>                 /* Only a few features are advertised in Intel's
> >>>                 0x80000001. */ regs[2] &= (is_64bit ?
> > bitmaskof(X86_FEATURE_LAHF_LM) : 0) |
> >>> 
> > bitmaskof(X86_FEATURE_ABM);
> >>>                 regs[3] &= ((is_pae ? bitmaskof(X86_FEATURE_NX) :
> >>> 0)
> > |
> >>>                             (is_64bit ? bitmaskof(X86_FEATURE_LM) : 0)
> >>>                             | (is_64bit ?
> >>>                             bitmaskof(X86_FEATURE_SYSCALL) : 0) |
> >>>                             (is_64bit ?
> > bitmaskof(X86_FEATURE_RDTSCP) : 0));
> >>>                 break;
> >>>             }
> >>> 
> >>> Which masks anything which is not explicitly mentioned. (PAGE1GB
> >>> is in regs[3], I think).
> >> 
> >> Ah, okay. The funs of white listing on HVM vs black listing on PV
> >> again.
> >> 
> >>> The AMD version is more permissive:
> >>> 
> >>>         regs[3] &= (0x0183f3ff | /* features shared with
> > 0x00000001:EDX */
> >>>                     (is_pae ? bitmaskof(X86_FEATURE_NX) : 0) |
> >>>                     (is_64bit ? bitmaskof(X86_FEATURE_LM) : 0) |
> >>>                     bitmaskof(X86_FEATURE_SYSCALL) |
> >>>                     bitmaskof(X86_FEATURE_MP) |
> >>>                     bitmaskof(X86_FEATURE_MMXEXT) |
> >>>                     bitmaskof(X86_FEATURE_FFXSR) |
> >>>                     bitmaskof(X86_FEATURE_3DNOW) |
> >>>                     bitmaskof(X86_FEATURE_3DNOWEXT));
> >>> (but I didn't check if PAGE1GB is in that magic number...)
> >> 
> >> It's not - it's bit 26.
> > 
> > So.. it sounds to me like everybody is in the agreement that this is
> > the right thing to do (enable it if the hypervisor has it enabled)?
> > 
> > And the next thing is actually come up with a patch to do some of this
> > plumbing - naturally for Xen 4.5?
> 
> Hi, Konrad,
> 
> Is there any patch to turn on the 1GB hugepages? If no, we are happy to give a patch to do it.

I have not see a patch for this, and I would be quite happy to see patch
developed for this!