Re: [Xen-devel] [PATCH v8 1/3] xen/libxc: Allow changing max number of hypervisor cpuid leaves

[Don Slutz <dslutz@xxxxxxxxxxx>]

On 04/22/14 08:41, Jan Beulich wrote:
> > > > On 22.04.14 at 14:32, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > On 04/22/2014 05:45 AM, Jan Beulich wrote:
> > > > > > On 21.04.14 at 23:57, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > > > +    if ( (limit < 2) || (limit > XEN_CPUID_MAX_NUM_LEAVES) )
> > > > +        limit = XEN_CPUID_MAX_NUM_LEAVES;
> > > Almost: If limit < 2, you would be better off using 2 rather than the
> > > default (which may be growing).
> > My thinking was that for any invalid limit value we should ignore what
> > the user file specified, not try to guess what was meant.
> And I think that 0 or 1 aren't really invalid - if a lower limit is wanted,
> provided as low as possible one rather than ignoring the request (I
> didn't look at what upsets hvmloader - I suppose this could be fixed
> rather than going with the slightly awkward lower limit of 2).
I think the routine init_hypercalls() is where hvmloader gets upset:

    /* Fill in hypercall transfer pages. */
    cpuid(base + 2, &eax, &ebx, &ecx, &edx);
    for ( i = 0; i < eax; i++ )
        wrmsr(ebx, HYPERCALL_PHYSICAL_ADDRESS + (i << 12) + i);


   -Don Slutz


> Jan
>
>
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