Re: [Xen-devel] [PATCH] x86: move vgc_flags to struct pv_vcpu

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 20/12/2019 14:55, Jan Beulich wrote:
> There's been effectively no use of the field for HVM.
>
> Also shrink the field to unsigned int, even if this doesn't immediately
> yield any space benefit for the structure itself. The resulting 32-bit
> padding slot can eventually be used for some other field. The change in
> size makes accesses slightly more efficient though, as no REX.W prefix
> is going to be needed anymore on the respective insns.
>
> Mirror the HVM side change here (dropping of setting the field to
> VGCF_online) also to Arm, on the assumption that it was cloned like
> this originally. VGCF_online really should simply and consistently be
> the guest view of the inverse of VPF_down, and hence needs representing
> only in the get/set vCPU context interfaces.
But vPSCI is just a wrapper to get/set vCPU context interfaces. Your 
changes below will clearly break bring-up of secondary vCPUs on Arm.
This is because arch_set_guest_info() will rely on this flag to 
clear/set VPF_down in the pause flags.
So I think the line in arm/vpsci.c should be left alone.

> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/xen/arch/arm/vpsci.c
> +++ b/xen/arch/arm/vpsci.c
> @@ -78,7 +78,6 @@ static int do_common_cpu_on(register_t t
>           ctxt->user_regs.x0 = context_id;
>       }
>   #endif
> -    ctxt->flags = VGCF_online; >
>       domain_lock(d);
>       rc = arch_set_info_guest(v, ctxt);
Cheers,

--
Julien Grall

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