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

[Sathyanarayanan Kuppuswamy]

On 5/3/22 3:28 PM, Sathyanarayanan Kuppuswamy wrote:
> 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.

I mean, I have already implemented the vmap based solution.

> 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