Re: [PATCH v17 18/23] platform/x86: Intel SGX driver

[Andy Lutomirski]

On Mon, Dec 17, 2018 at 12:03 PM Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
>
> On 12/17/18 11:55 AM, Andy Lutomirski wrote:
> >> You're effectively rebuilding reverse-mapping infrastructure here.  It's
> >> a frequent thing for the core VM to need to go from 'struct page' back
> >> to the page tables mapping it.  For that we go (logically)
> >> page->{anon_vma,mapping}->vma->vm_mm->pagetable.
> > This is a bit outside my expertise here, but doesn't
> > unmap_mapping_range() do exactly what SGX wants?
>
> There's no 'struct page' for enclave memory as it stands.  That means no
> page cache, and that means there's no 'struct address_space *mapping' in
> the first place.
>
> Basically, the choice was made a long time ago to have SGX's memory
> management live outside the core VM.  I've waffled back and forth on it,
> but I do still think this is the right way to do it.

AFAICS a lack of struct page isn't a problem.  The core code seems to
understand that address_space objects might cover non-struct-page
memory.  Morally, enclave memory is a lot like hot-unpluggable PCI
space.