Re: [RFC PATCH 00/14] Prevent cross-cache attacks in the SLUB allocator

[Linus Torvalds]

On Tue, 19 Sept 2023 at 08:48, Matteo Rizzo <matteorizzo@xxxxxxxxxx> wrote:
>
> On Mon, 18 Sept 2023 at 20:05, Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > ... and equally importantly, what about DMA?
>
> I'm not exactly sure what you mean by this, I don't think this should
> affect the performance of DMA.

I was more worried about just basic correctness.

We've traditionally had a lot of issues with using virtual addresses
for dma, simply because we've got random drivers, and I'm not entirely
convinced that your "virt_to_phys()" update will catch it all.

IOW, even on x86-64 - which is hopefully better than most
architectures because it already has that double mapping issue - we
have things like

        unsigned long paddr = (unsigned long)vaddr - __PAGE_OFFSET;

in other places than just the __phys_addr() code.

The one place I grepped for looks to be just boot-time AMD memory
encryption, so wouldn't be any slab allocation, but ...

               Linus