On 05/04/16 11:45, David Vrabel wrote:
> On 05/04/16 06:10, Juergen Gross wrote:
>> Some hardware models (e.g. Dell Studio 1555 laptops) require calls to
>> the firmware to be issued on cpu 0 only. As Dom0 might have to use
>> these calls, add xen_pin_vcpu() to achieve this functionality.
>>
>> In case either the domain doesn't have the privilege to make the
>> related hypercall or the hypervisor isn't supporting it, issue a
>> warning once and disable further pinning attempts.
> [...]
>> --- a/arch/x86/xen/enlighten.c
>> +++ b/arch/x86/xen/enlighten.c
>> @@ -1885,6 +1885,45 @@ static void xen_set_cpu_features(struct cpuinfo_x86 *c)
>> }
>> }
>>
>> +static void xen_pin_vcpu(int cpu)
>> +{
>> + static bool disable_pinning;
>> + struct sched_pin_override pin_override;
>> + int ret;
>> +
>> + if (disable_pinning)
>> + return;
>> +
>> + pin_override.pcpu = cpu;
>> + ret = HYPERVISOR_sched_op(SCHEDOP_pin_override, &pin_override);
>
> /* Ignore errors when removing override. */
Okay.
>> + if (cpu < 0)
>> + return;
>> +
>> + switch (ret) {
>> + case -ENOSYS:
>> + pr_warn("The kernel tried to call a function on physical cpu %d, but Xen isn't\n"
>> + "supporting this. In case of problems you might consider vcpu pinning.\n",
>> + cpu);
>> + disable_pinning = true;
>> + break;
>> + case -EPERM:
>> + WARN(1, "Trying to pin vcpu without having privilege to do so\n");
>> + disable_pinning = true;
>> + break;
>> + case -EINVAL:
>> + case -EBUSY:
>> + pr_warn("The kernel tried to call a function on physical cpu %d, but this cpu\n"
>> + "seems not to be available. Please check your Xen cpu configuration.\n",
>> + cpu);
>> + break;
>> + case 0:
>> + break;
>> + default:
>> + WARN(1, "rc %d while trying to pin vcpu\n", ret);
>> + disable_pinning = true;
>> + }
>
> These messages are a bit wordy for my taste and since they don't say
> what function failed or what driver is affected they're not as useful as
Did you notice I used WARN() for the cases where a usage error is to
be suspected? This will print a stack backtrace helping to identify the
driver.
I can work on the message text, of course.
> they could be. I'd probably turn these all into:
>
> if (cpu >= 0 && ret < 0) {
> pr_warn("Failed to pin VCPU %d to physical CPU %d: %d",
> smp_processor_id(), cpu, ret);
> disable_pinning = true;
> }
No, I don't think this is a good idea. In the EINVAL or EBUSY case a
simple Xen admin command might be enough to make the next call succeed.
I don't want to disable pinning in this case.
> And look at getting the user of this API to print a more useful error.
>
> "i8k: unable to call SMM BIOS on physical CPU %d: %d"
TBH: I think this should be done by another patch. This is something
the maintainers of the callers' code should decide.
Juergen
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