Re: [PATCH v2 3/4] drm/ttm, drm/vmwgfx: Correctly support support AMD memory encryption

From: Daniel Vetter
Date: Wed Sep 04 2019 - 03:54:07 EST

On Wed, Sep 4, 2019 at 8:49 AM Thomas HellstrÃm (VMware)
<thomas_os@xxxxxxxxxxxx> wrote:
> On 9/4/19 1:15 AM, Andy Lutomirski wrote:
> > But, reading this, I have more questions:
> >
> > Canât you get rid of cvma by using vmf_insert_pfn_prot()?
> It looks like that, although there are comments in the code about
> serious performance problems using VM_PFNMAP / vmf_insert_pfn() with
> write-combining and PAT, so that would require some serious testing with
> hardware I don't have. But I guess there is definitely room for
> improvement here. Ideally we'd like to be able to change the
> vma->vm_page_prot within fault(). But we can

Just a quick comment on this: It's the repeated (per-pfn/pte) lookup
of the PAT tables, which are dead slow. If you have a struct
io_mapping then that can be done once, and then just blindly inserted.
See remap_io_mapping in i915.
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 -