Re: [Xen-devel] [PATCH 06/13] libx86: Introduce a helper to serialise a cpuid_policy object

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/07/18 09:11, Wei Liu wrote:
> On Wed, Jul 04, 2018 at 05:46:29PM +0100, Andrew Cooper wrote:
>> On 04/07/18 10:01, Jan Beulich wrote:
>>>>>> On 03.07.18 at 22:55, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>> --- a/xen/common/libx86/cpuid.c
>>>> +++ b/xen/common/libx86/cpuid.c
>>>> @@ -34,6 +34,100 @@ const uint32_t *x86_cpuid_lookup_deep_deps(uint32_t 
>>>> feature)
>>>>  }
>>>>  
>>>>  /*
>>>> + * Copy a single cpuid_leaf into a provided xen_cpuid_leaf_t buffer,
>>>> + * performing boundary checking against the buffer size.
>>>> + */
>>>> +static int copy_leaf_to_buffer(uint32_t leaf, uint32_t subleaf,
>>>> +                               const struct cpuid_leaf *data,
>>>> +                               cpuid_leaf_buffer_t leaves,
>>>> +                               uint32_t *curr_entry, const uint32_t 
>>>> nr_entries)
>>>> +{
>>>> +    const xen_cpuid_leaf_t val = {
>>>> +        leaf, subleaf, data->a, data->b, data->c, data->d,
>>>> +    };
>>>> +
>>>> +    if ( *curr_entry == nr_entries )
>>>> +        return -ENOBUFS;
>>>> +
>>>> +    if ( copy_to_buffer_offset(leaves, *curr_entry, &val, 1) )
>>>> +        return -EFAULT;
>>>> +
>>>> +    ++*curr_entry;
>>> Following on from what Wei has said - you don't mean to have a way
>>> here then to indicate to a higher up caller how many slots would have
>>> been needed?
>> I don't understand your query.  An individual build has a compile-time
>> static maximum number of leaves, and this number can be obtained in the
>> usual way by making a hypercall with a NULL guest handle.
> Ah, this is what I was looking for. I think this should be wrapped into
> a function btw.

It is.  xc_get_cpumsr_policy_size(), in patch 9 where it is first used.

~Andrew

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