Re: [PATCH v5 3/3] x86/tdx: Add Quote generation support

From: Sathyanarayanan Kuppuswamy
Date: Tue May 03 2022 - 18:28:52 EST




On 5/3/22 3:24 PM, Dave Hansen wrote:
On 5/2/22 18:27, Kirill A. Shutemov wrote:
Again, Dave and Andi already commented you should use vmap() to avoid breaking
up the direct-mapping. Please use vmap() instead.

https://lore.kernel.org/all/ce0feeec-a949-35f8-3010-b0d69acbbc2e@xxxxxxxxxxxxxxx/

Will review the rest later.
I would rather convert it to use DMA API for memory allocation. It will
tap into swiotlb buffer that already converted and there's no need to
touch direct mapping. Both allocation and freeing such memory is cheaper
because of that.

Sathya, I don't quite understand why you are so forcefully declining to
incorporate review feedback on this point. I gave very specific
feedback about the kind of mapping you need and that you should avoid
fragmenting the direct map if at all possible.

Why is this code still fragmenting the direct map?

I have already implemented it and testing it now.

In this discussion, we are comparing the use of DMA API for memory
allocation vs vmap/sharing it in driver itself.

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer