Re: [PATCH] x86/CPU: don't hard-code MTRR availability

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Mar 25, 2025 at 08:18:11AM +0100, Jan Beulich wrote:
> In particular if we're running virtualized, the underlying hypervisor
> (which may be another Xen) may not surface MTRRs, and offer PAT only.

At least for Xen, I think we offer MTRR uniformly, even on PVH
guests?

> Fixes: 5a281883cdc3 ("Hardcode many cpu features for x86/64 -- we know 
> 64-bit")
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

My main concern is whether the !mtrr path is still functional.  Have
you tried booting the resulting hypervisor with MTRR masked on CPUID?

(or alternatively short-circuiting cpu_has_mtrr == 0?)

Thanks, Roger.