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Date: Tue, 12 Oct 2021 09:43:18 +0200
From: "Gerd Hoffmann" <kraxel@redhat.com>
To: Min Xu <min.m.xu@intel.com>
Cc: devel@edk2.groups.io, Ard Biesheuvel <ardb+tianocore@kernel.org>,
	Jordan Justen <jordan.l.justen@intel.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Erdem Aktas <erdemaktas@google.com>,
	James Bottomley <jejb@linux.ibm.com>,
	Jiewen Yao <jiewen.yao@intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>
Subject: Re: [PATCH V9 4/4] OvmfPkg: Enable TDX in ResetVector
Message-ID: <20211012074318.evyxxk67jbbauv57@sirius.home.kraxel.org>
References: <cover.1634005437.git.min.m.xu@intel.com>
 <b5fad086a9804b80cab90d4fa2d035d550355a4c.1634005437.git.min.m.xu@intel.com>
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  Hi,

> +; Load the GDT and set the CR0.
> +;
> +; Modified:  EAX, EBX, CR0, CR4, DS, ES, FS, GS, SS, CS
> +;
> +ReloadFlat32:
> +
> +    cli
> +    mov     ebx, ADDR_OF(gdtr)
> +    lgdt    [ebx]

No need to modify ebx here, eax should do fine.

> +    mov     eax, SEC_DEFAULT_CR0
> +    mov     cr0, eax
> +
> +    jmp     LINEAR_CODE_SEL:dword ADDR_OF(jumpToFlat32BitAndLandHere)
> +
> +jumpToFlat32BitAndLandHere:

Strictly speaking this is not correct, you are already in Flat32 mode,
so this only loads cs.

> +InitTdx:
> +    ;
> +    ; Save EBX in EBP because EBX will be changed in ReloadFlat32
> +    ;
> +    mov     ebp, ebx

See above, there is no need to modify ebx in ReloadFlat32.
Also: seems ebx is never restored ...

take care,
  Gerd