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
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