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Subject: Re: [edk2-devel] [RFC PATCH v2 39/44] OvmfPkg: Move the GHCB allocations into reserved memory
To: devel@edk2.groups.io, thomas.lendacky@amd.com
References: <cover.1568922728.git.thomas.lendacky@amd.com>
 <7a169f2dd9e6ae7f266b8ef2b690865dc04b4764.1568922729.git.thomas.lendacky@amd.com>
From: "Laszlo Ersek" <lersek@redhat.com>
Message-ID: <25b37eb8-992d-fccf-ee76-d1b06f7f8cbf@redhat.com>
Date: Wed, 2 Oct 2019 16:38:36 +0200
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On 09/20/19 15:16, Lendacky, Thomas wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
> 
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198
> 
> After having transitioned from UEFI to the OS, the OS will need to boot
> the APs. For an SEV-ES guest, the APs will have been parked by UEFI using
> GHCB pages allocated by UEFI. The hypervisor will write to the GHCB
> SW_EXITINFO2 field of the GHCB when the AP is booted. As a result, the
> GHCB pages must be marked reserved so that the OS does not attempt to use
> them and experience memory corruption because of the hypervisor write.
> 
> Change the GHCB allocation from the default boot services memory to
> reserved memory.
> 
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  OvmfPkg/PlatformPei/AmdSev.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
> index d6733447bdf2..53eeb59702ae 100644
> --- a/OvmfPkg/PlatformPei/AmdSev.c
> +++ b/OvmfPkg/PlatformPei/AmdSev.c
> @@ -49,9 +49,11 @@ AmdSevEsInitialize (
>  
>    //
>    // Allocate GHCB pages.
> +  //   Since the pages must survive across the UEFI to OS transition
> +  //   make them reserved.
>    //
>    GhcbPageCount = mMaxCpuCount * 2;
> -  GhcbBase = AllocatePages (GhcbPageCount);
> +  GhcbBase = AllocateReservedPages (GhcbPageCount);
>    ASSERT (GhcbBase);
>  
>    GhcbBasePa = (PHYSICAL_ADDRESS)(UINTN) GhcbBase;
> 

Reviewed-by: Laszlo Ersek <lersek@redhat.com>