Re: [Xen-devel] [PATCH 4/5] x86/pv: Drop support for paging out the LDT

[Doug Goldstein <cardoe@xxxxxxxxxx>]

On 1/12/18 12:37 PM, Andrew Cooper 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.
> 
> The for_each_vcpu() is one scalability limitation for PV guests, which can't
> reasonably be altered to be continuable.
> 
> One side effects of dropping paging out support is that now, the LDT (like the
> GDT) is only ever modified in current context, allowing us to drop
> shadow_ldt_mapcnt and shadow_ldt_lock from struct vcpu.
> 
> Another side effect is that the LDT no longer automatically cleans itself up
> on domain destruction.  Cover this by explicitly releasing the LDT frames at
> the same time as the GDT frames.
> 
> Finally, leave some asserts around to confirm the expected behaviour of all
> the functions playing with PGT_seg_desc_page references.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Makes sense to me and the code looks good.

Reviewed-by: Doug Goldstein <cardoe@xxxxxxxxxx>

-- 
Doug Goldstein

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