Re: [PATCH v3] drm/ttm: Make sure the mapped tt pages are decrypted when needed

[Christian König]

Am 26.01.24 um 06:10 schrieb Zack Rusin:
> On Fri, Jan 5, 2024 at 8:51 AM Zack Rusin <zack.rusin@xxxxxxxxxxxx> wrote:
> > Some drivers require the mapped tt pages to be decrypted. In an ideal
> > world this would have been handled by the dma layer, but the TTM page
> > fault handling would have to be rewritten to able to do that.
> >
> > A side-effect of the TTM page fault handling is using a dma allocation
> > per order (via ttm_pool_alloc_page) which makes it impossible to just
> > trivially use dma_mmap_attrs. As a result ttm has to be very careful
> > about trying to make its pgprot for the mapped tt pages match what
> > the dma layer thinks it is. At the ttm layer it's possible to
> > deduce the requirement to have tt pages decrypted by checking
> > whether coherent dma allocations have been requested and the system
> > is running with confidential computing technologies.
> >
> > This approach isn't ideal but keeping TTM matching DMAs expectations
> > for the page properties is in general fragile, unfortunately proper
> > fix would require a rewrite of TTM's page fault handling.
> >
> > Fixes vmwgfx with SEV enabled.
> >
> > v2: Explicitly include cc_platform.h
> > v3: Use CC_ATTR_GUEST_MEM_ENCRYPT instead of CC_ATTR_MEM_ENCRYPT to
> > limit the scope to guests and log when memory decryption is enabled.
> Hi, Christian.
>
> Gentle ping on that one. This is probably the cleanest we can get this
> code. Can we land this or is there anything else you'd like to see?

Sorry for the delay.

I'm not too familiar with the technical background, so I can't 100% 
judge if this is correct or not.

But if it works for you I think we should give it a try, feel free to 
add my Acked-by and push upstream through whatever branch you like.

Regards,
Christian.

> z