Re: [PATCH v2 1/2] x86/xen: remove xen_have_vcpu_info_placement flag

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 9/22/21 6:31 AM, Juergen Gross wrote:
>  
> -     if (xen_have_vcpu_info_placement) {
> -             vcpup = &per_cpu(xen_vcpu_info, cpu);
> -             info.mfn = arbitrary_virt_to_mfn(vcpup);
> -             info.offset = offset_in_page(vcpup);
> +     vcpup = &per_cpu(xen_vcpu_info, cpu);
> +     info.mfn = arbitrary_virt_to_mfn(vcpup);
> +     info.offset = offset_in_page(vcpup);
>  
> -             /*
> -              * Check to see if the hypervisor will put the vcpu_info
> -              * structure where we want it, which allows direct access via
> -              * a percpu-variable.
> -              * N.B. This hypercall can _only_ be called once per CPU.
> -              * Subsequent calls will error out with -EINVAL. This is due to
> -              * the fact that hypervisor has no unregister variant and this
> -              * hypercall does not allow to over-write info.mfn and
> -              * info.offset.
> -              */
> -             err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info,
> -                                      xen_vcpu_nr(cpu), &info);
> -
> -             if (err) {
> -                     pr_warn_once("register_vcpu_info failed: cpu=%d 
> err=%d\n",
> -                                  cpu, err);
> -                     xen_have_vcpu_info_placement = 0;
> -             } else {
> -                     /*
> -                      * This cpu is using the registered vcpu info, even if
> -                      * later ones fail to.
> -                      */
> -                     per_cpu(xen_vcpu, cpu) = vcpup;
> -             }
> -     }
> -
> -     if (!xen_have_vcpu_info_placement)
> -             xen_vcpu_info_reset(cpu);
> +     /*
> +      * N.B. This hypercall can _only_ be called once per CPU.
> +      * Subsequent calls will error out with -EINVAL. This is due to
> +      * the fact that hypervisor has no unregister variant and this
> +      * hypercall does not allow to over-write info.mfn and
> +      * info.offset.
> +      */
> +     err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, xen_vcpu_nr(cpu),
> +                              &info);
> +     if (err)
> +             panic("register_vcpu_info failed: cpu=%d err=%d\n", cpu, err);
>  


This is change in behavior. Before if the hypercall failed we still try to 
boot. I am not sure we need to worry about this (since it's not clear it 
actually works)  but I'd at least mention this in the commit message.


-boris