Re: [PATCH, RFC 45/62] mm: Add the encrypt_mprotect() system call for MKTME

[Andy Lutomirski]

On Mon, Jun 17, 2019 at 6:34 PM Lendacky, Thomas
<Thomas.Lendacky@xxxxxxx> wrote:
>
> On 6/17/19 6:59 PM, Kai Huang wrote:
> > On Mon, 2019-06-17 at 11:27 -0700, Dave Hansen wrote:

> >
> > And yes from my reading (better to have AMD guys to confirm) SEV guest uses anonymous memory, but it
> > also pins all guest memory (by calling GUP from KVM -- SEV specifically introduced 2 KVM ioctls for
> > this purpose), since SEV architecturally cannot support swapping, migraiton of SEV-encrypted guest
> > memory, because SME/SEV also uses physical address as "tweak", and there's no way that kernel can
> > get or use SEV-guest's memory encryption key. In order to swap/migrate SEV-guest memory, we need SGX
> > EPC eviction/reload similar thing, which SEV doesn't have today.
>
> Yes, all the guest memory is currently pinned by calling GUP when creating
> an SEV guest.

Ick.

What happens if QEMU tries to read the memory?  Does it just see
ciphertext?  Is cache coherency lost if QEMU writes it?