Re: [Xen-devel] [PATCH RFC 31/44] x86/pv: Drop support for paging out the LDT

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.01.18 at 21:21, <andrew.cooper3@xxxxxxxxxx> wrote:
> Windows is the only OS which pages out kernel datastructures, so chances are
> good that this is a vestigial remnant of the PV Windows XP experiment.
> Furthermore the implementation is incomplete; it only functions for a present
> => not-present transition, rather than a present => read/write transition.

I've thought about this some more. For one, I don't understand the
"read/write" part above: descriptor table pages aren't permitted to
be writable in the first place. Did you mean "present -> present"? If
so, put_page_from_l1e() also gets called when an L1E is being
replaced, so it would seem to me that this (sub)case is handled
properly.

What instead isn't handled is the case where a higher level page
table entry mapping the LDT is being replaced.

Jan


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