Re: [Xen-devel] [PATCH RFC 2/4] xen: grant_table: implement grant_table_soft_reset()

[Tim Deegan <tim@xxxxxxx>]

At 16:22 +0100 on 04 Jun (1433434934), David Vrabel wrote:
> On 04/06/15 15:11, Tim Deegan wrote:
> > 
> > There has been talk before of an operation along the lines of "revoke
> > this grant entry and wait for all users to release it" but that would
> > only help with backends that are guaranteed to release grants in a
> > reasonable time.
> 
> Are you talking about my idea? This would be immediate because the grant
> mapper would provide a local page to atomically switch the foreign
> mapping to when the grant is revoked.

That's a stronger operation than I remembered, and similar to what's
happening here.

If this reset operation is to be called from the guest, then all the
guest can do is reshuffle its own memory -- it can't expect to have
enough spare memory to cover all outstanding granted pages.

But TBH this is a bit of a red herring; I ought not to have mentioned
it. :)

Tim.

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