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SubjectRe: [PATCH v2 1/2] x86/xen: remove xen_have_vcpu_info_placement flag
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On 22.09.21 23:43, Boris Ostrovsky wrote:
>
> 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.

Hmm, maybe I should have been more explicit saying that the hypercall
was introduced in Xen 3.4, and only reason of failure is either an
illegal vcpu, an invalid mapping specification, or a try to reissue the
hypercall for a vcpu. None of those should ever happen.


Juergen
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