Re: [edk2-devel] [PATCH 10/16] MdePkg: GHCB APIC ID retrieval support definitions

["Gerd Hoffmann" <kraxel@redhat.com>]

On Fri, Jan 26, 2024 at 04:13:09PM -0600, Tom Lendacky wrote:
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4654
> 
> When an SVSM is present, starting the APs requires knowledge of the APIC
> IDs. Create the definitions required to retrieve and hold the APIC ID
> information of all the vCPUs present in the guest.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  MdePkg/Include/Register/Amd/Ghcb.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/MdePkg/Include/Register/Amd/Ghcb.h b/MdePkg/Include/Register/Amd/Ghcb.h
> index 29b2e45d0163..cb581b14723d 100644
> --- a/MdePkg/Include/Register/Amd/Ghcb.h
> +++ b/MdePkg/Include/Register/Amd/Ghcb.h
> @@ -56,6 +56,7 @@
>  #define SVM_EXIT_AP_JUMP_TABLE          0x80000005ULL
>  #define SVM_EXIT_SNP_PAGE_STATE_CHANGE  0x80000010ULL
>  #define SVM_EXIT_SNP_AP_CREATION        0x80000013ULL
> +#define SVM_EXIT_GET_APIC_IDS           0x80000017ULL
>  #define SVM_EXIT_HYPERVISOR_FEATURES    0x8000FFFDULL
>  #define SVM_EXIT_UNSUPPORTED            0x8000FFFFULL
>  
> @@ -170,6 +171,7 @@ typedef union {
>  #define GHCB_HV_FEATURES_SNP_AP_CREATE                   (GHCB_HV_FEATURES_SNP | BIT1)
>  #define GHCB_HV_FEATURES_SNP_RESTRICTED_INJECTION        (GHCB_HV_FEATURES_SNP_AP_CREATE | BIT2)
>  #define GHCB_HV_FEATURES_SNP_RESTRICTED_INJECTION_TIMER  (GHCB_HV_FEATURES_SNP_RESTRICTED_INJECTION | BIT3)
> +#define GHCB_HV_FEATURES_APIC_ID_LIST                    BIT4
>  
>  //
>  // SNP Page State Change.
> @@ -203,6 +205,14 @@ typedef struct {
>  #define SNP_PAGE_STATE_MAX_ENTRY   \
>    ((sizeof (((GHCB *)0)->SharedBuffer) - sizeof (SNP_PAGE_STATE_HEADER)) / sizeof (SNP_PAGE_STATE_ENTRY))
>  
> +//
> +// Get APIC IDs
> +//
> +typedef struct {
> +  UINT32    NumEntries;
> +  UINT32    ApicIds[];
> +} GHCB_APIC_IDS;

So with GHCB being one page in size this interface
can handle at most 1023 vCPUs, right?

Any plans to handle guest larger than that?

Given this just adds the interface defined by the spec so this is a
concern for the spec not the patch:
Acked-by: Gerd Hoffmann <kraxel@redhat.com>

take care,
  Gerd



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