Re: [edk2-devel] [PATCH 07/14] OvmfPkg: Add PCD and DEFINEs for Lazy Accept page.

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

On 6/16/22 00:51, Gerd Hoffmann wrote:
>    Hi,
> 
>>> Tom Lendacky's suggestion for SEV-SNP is to pre-accept all memory under
>>> 4GB to make all that complexity go away. Only this approach worked in my
>>> own testing. With the MMIO hole it's just validating 3GB of memory.
>> Accepting all memory under 4GB will make the things much simpler. In this way I think the accept-on-demand maybe not needed.
>> A question: is there some performance impact when accepting all memory under 4GB?
> 
> That would certainly be easiest when it is acceptable from a performance
> point of view.  Will also simplify the code because you don't have to
> split the low memory block into accepted/unaccepted parts.
> 
> It'll be 3G (-machine pc) or 2G (-machine q35) of memory.
> Is it possible to accept gigabyte pages btw?

+Ashish/Mike - I thought I had added them earlier...

SNP supports 4K and 2MB. However, SNP can support multiple pages in a 
single Page State Change GHCB request. This might be better than having to 
exit once for every on-demand page.

Thanks,
Tom

> 
> And, yes, this might be enough that accept-on-demand is not needed any
> more.
> 
> take care,
>    Gerd
>