Re: [RFC v2 01/32] x86/paravirt: Introduce CONFIG_PARAVIRT_XL

[Andi Kleen]

On 5/12/2021 6:18 AM, Peter Zijlstra wrote:
> On Mon, May 10, 2021 at 05:56:05PM +0200, Juergen Gross wrote:
>
> > No. We have PARAVIRT_XXL for Xen PV guests, and we have PARAVIRT for
> > other hypervisor's guests, supporting basically the TLB flush operations
> > and time related operations only. Adding the halt related operations to
> > PARAVIRT wouldn't break anything.
> Also, I don't think anything modern should actually ever hit any of the
> HLT instructions, most everything should end up at an MWAIT.
>
> Still, do we wants to give arch_safe_halt() and halt() the
> PVOP_ALT_VCALL0() treatment?

From performance reasons it's pointless to patch. HLT (and MWAIT) are 
so slow anyways that using patching or an indirect pointer is completely 
in the noise. So I would use whatever is cleanest in the code.

-Andi