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References: <cover.1628767741.git.min.m.xu@intel.com> <8f56e6f50477bf00d5121e6515388fe68525b1e2.1628767741.git.min.m.xu@intel.com>
In-Reply-To: <8f56e6f50477bf00d5121e6515388fe68525b1e2.1628767741.git.min.m.xu@intel.com>
From: "Erdem Aktas" <erdemaktas@google.com>
Date: Sat, 11 Sep 2021 04:15:30 +0300
Message-ID: <CAAYXXYxJmo1Sb7pmctW7EDj0yFM9CyteZX1UQdgpfQ4BeUeMWw@mail.gmail.com>
Subject: Re: [PATCH 07/23] MdePkg: Update BaseIoLibIntrinsicSev to support Tdx
To: Min Xu <min.m.xu@intel.com>
Cc: edk2-devel-groups-io <devel@edk2.groups.io>, Michael D Kinney <michael.d.kinney@intel.com>, 
	Liming Gao <gaoliming@byosoft.com.cn>, Zhiguang Liu <zhiguang.liu@intel.com>, 
	Brijesh Singh <brijesh.singh@amd.com>, James Bottomley <jejb@linux.ibm.com>, 
	Jiewen Yao <jiewen.yao@intel.com>, Tom Lendacky <thomas.lendacky@amd.com>
Content-Type: text/plain; charset="UTF-8"

On Thu, Aug 12, 2021 at 2:57 PM Min Xu <min.m.xu@intel.com> wrote:
 > +UINT8
> +EFIAPI
> +TdMmioRead8 (
> +  IN      UINTN                     Address
> +  )
> +{
> +  UINT64                             Value;
> +  UINT64                             Status;
> +
> +  Address |= TdSharedPageMask ();

Why is the SharedBit set? VMM does not care if the sharedbit is set.
Actually it should not even be aware of it.
> +  MemoryFence ();
> +  Status = TdVmCall (TDVMCALL_MMIO, TDVMCALL_ACCESS_SIZE_1, TDVMCALL_ACCESS_READ, Address, 0, &Value);
> +  if (Status != 0) {
So for some reason, MMIO read fails, we are doing a memory read. Why
should an MMIO read fail? Could you elaborate which use case this
covers?