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

[Sathyanarayanan Kuppuswamy]

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