On 31.10.19 16:41, Christian Borntraeger wrote:
On 25.10.19 10:49, David Hildenbrand wrote:
On 24.10.19 13:40, Janosch Frank wrote:
From: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Pin the guest pages when they are first accessed, instead of all at
the same time when starting the guest.
Please explain why you do stuff. Why do we have to pin the hole guest memory? Why can't we mlock() the hole memory to avoid swapping in user space?
Basically we pin the guest for the same reason as AMD did it for their SEV. It is hard
Pinning all guest memory is very ugly. What you want is "don't page",
what you get is unmovable pages all over the place. I was hoping that
you could get around this by having an automatic back-and-forth
conversion in place (due to the special new exceptions).
to synchronize page import/export with the I/O for paging. For example you can actually
fault in a page that is currently under paging I/O. What do you do? import (so that the
guest can run) or export (so that the I/O will work). As this turned out to be harder then
we though we decided to defer paging to a later point in time.
I don't quite see the issue yet. If you page out, the page will
automatically (on access) be converted to !secure/encrypted memory. If
the UV/guest wants to access it, it will be automatically converted to
secure/unencrypted memory. If you have concurrent access, it will be
converted back and forth until one party is done.
A proper automatic conversion should make this work. What am I missing?
As we do not want to rely on the userspace to do the mlock this is now done in the kernel.
I wonder if we could come up with an alternative (similar to how we
override VM_MERGEABLE in the kernel) that can be called and ensured in
the kernel. E.g., marking whole VMAs as "don't page" (I remember
something like "special VMAs" like used for VDSOs that achieve exactly
that, but I am absolutely no expert on that). That would be much nicer
than pinning all pages and remembering what you pinned in huge page
arrays ...
--
Thanks,
David / dhildenb
