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Date: Wed, 13 Oct 2021 06:49:25 +0200
From: "Gerd Hoffmann" <kraxel@redhat.com>
To: devel@edk2.groups.io, min.m.xu@intel.com
Cc: 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: [edk2-devel] [PATCH V2 21/28] OvmfPkg: Update PlatformPei to support TDX
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  Hi,

> 2. Relocate mailbox
>   At the beginning of system boot, a 4K-aligned, 4K-size memory (Td
>   mailbox) is pre-allocated by host VMM. BSP & APs do the page accept
>   together in that memory region.
>   After that TDVF is designed to relocate the mailbox to a 4K-aligned,
>   4K-size memory block which is allocated in the ACPI Nvs memory. APs
>   are waken up and spin around the relocated mailbox waiting for
>   further command.

Why is the mailbox relocated?  Are there any problems when simply
continuing to use the memfd page?

The memfd page location is known to qemu, so when not relocating the
mailbox the MADT update could be done on the host side.

take care,
  Gerd