[edk2-devel] [RFC PATCH 01/19] OvmfPkg: Reserve the Secrets and Cpuid page for the SEV-SNP guest

James Bottomley jejb at linux.ibm.com
Wed Apr 7 00:44:52 UTC 2021


On Wed, 2021-04-07 at 00:21 +0000, Xu, Min M wrote:
> Hi, Laszlo
> 
> For Intel TDX supported guest, all processors start in 32-bit
> protected
> mode, while for Non-Td guest, it starts in 16-bit real mode. To make
> the
> ResetVector work on both Td-guest and Non-Td guest, ResetVector are
> updated as below:
> ------------------------------------------------------------------
>   ALIGN   16
>   resetVector:
>   ;
>   ; Reset Vector
>   ;
>   ; This is where the processor will begin execution
>   ;
>       nop
>       nop
>       smsw    ax
>       test    al, 1
>       jnz     EarlyBspPmEntry
>       jmp     EarlyBspInitReal16

Well, then use the rel8 jump like the compiler would in this situation:

      smsw    ax
      test    al, 1
      jz      1f
      jmp     EarlyBspPmEntry
1:
      jmp     EarlyBspInitReal16

So now both entries can be 32k away.

James




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