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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Jul 03, 2018 at 09:55:19PM +0100, Andrew Cooper wrote:
> The serialised form is made up of the leaf, subleaf and data tuple.  As this
> is the architectural form, it is expected not to change going forwards.
> 
> x86_cpuid_copy_to_buffer() is implemented using Xen's regular copy_to_guest
> primitives, with an API-compatible memcpy() is used for the libxc half of the
> build.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
[...]
> diff --git a/xen/include/public/arch-x86/xen.h 
> b/xen/include/public/arch-x86/xen.h
> index 69ee4bc..f3bdd83 100644
> --- a/xen/include/public/arch-x86/xen.h
> +++ b/xen/include/public/arch-x86/xen.h
> @@ -314,6 +314,17 @@ struct xen_arch_domainconfig {
>  #define XEN_ACPI_GPE0_CPUHP_BIT      2
>  #endif
>  
> +/*
> + * Representations of architectural CPUID information.  Used as the
> + * serialised version of Xen's internal representation.
> + */
> +typedef struct xen_cpuid_leaf {
> +#define XEN_CPUID_NO_SUBLEAF 0xffffffffu
> +    uint32_t leaf, subleaf;
> +    uint32_t a, b, c, d;
> +} xen_cpuid_leaf_t;
> +DEFINE_XEN_GUEST_HANDLE(xen_cpuid_leaf_t);
> +

Is putting this in public header while leaving
CPUID_MAX_SERIALISED_LEAVES in a private header useful?

How does an external user know how big a buffer it needs to provide to
accommodate the return structure?

Wei.

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