Re: [PATCH] x86/hvm: Extend HVM cpuid leaf with vcpu id

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Nov 06, 2014 at 03:07:10PM +0000, Paul Durrant wrote:
> To perform certain hypercalls HVM guests need to use Xen's idea of

What are those 'certain'?

> vcpu id, which may well not match the guest OS idea of CPU id.

Can you elaborate more on the use case please? And why
only restrict this to HVM guests? Why not PV?

> This patch adds vcpu id to the HVM cpuid leaf allowing the guest
> to build a mapping.

Don't we have existing hypercalls to get this? Ah VCPUOP_get_physid
is what I was thinking of and that does not seem to be what
you want?
> 
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> Cc: Keir Fraser <keir@xen.org>
> Cc: Jan Beulich <jbeulich@suse.com>
> ---
>  xen/arch/x86/hvm/hvm.c              |    4 ++++
>  xen/include/public/arch-x86/cpuid.h |    5 +++--
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 78f519d..d9a5706 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -4189,6 +4189,10 @@ void hvm_hypervisor_cpuid_leaf(uint32_t sub_idx,
>           * foreign pages) has valid IOMMU entries.
>           */
>          *eax |= XEN_HVM_CPUID_IOMMU_MAPPINGS;
> +
> +        /* Indicate presence of vcpu id and set it in ebx */
> +        *eax |= XEN_HVM_CPUID_VCPU_ID_PRESENT;
> +        *ebx = current->vcpu_id;
>      }
>  }
>  
> diff --git a/xen/include/public/arch-x86/cpuid.h b/xen/include/public/arch-x86/cpuid.h
> index 6005dfe..8ccb6e1 100644
> --- a/xen/include/public/arch-x86/cpuid.h
> +++ b/xen/include/public/arch-x86/cpuid.h
> @@ -76,13 +76,14 @@
>  /*
>   * Leaf 5 (0x40000x04)
>   * HVM-specific features
> + * EAX: Features
> + * EBX: VCPU ID
>   */
> -
> -/* EAX Features */
>  #define XEN_HVM_CPUID_APIC_ACCESS_VIRT (1u << 0) /* Virtualized APIC registers */
>  #define XEN_HVM_CPUID_X2APIC_VIRT      (1u << 1) /* Virtualized x2APIC accesses */
>  /* Memory mapped from other domains has valid IOMMU entries */
>  #define XEN_HVM_CPUID_IOMMU_MAPPINGS   (1u << 2)
> +#define XEN_HVM_CPUID_VCPU_ID_PRESENT  (1u << 3) /* vcpu is present in EBX */
>  
>  #define XEN_CPUID_MAX_NUM_LEAVES 4
>  
> -- 
> 1.7.10.4
> 
> 
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