[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC] DOMCTL_memattrs_op : a new DOMCTL to play with stage-2 page attributes
On 07/07/2017 08:27 AM, Jan Beulich wrote: >>>> On 06.07.17 at 20:07, <julien.grall@xxxxxxx> wrote: >> On 07/06/2017 06:42 PM, Stefano Stabellini wrote: >>> On Thu, 6 Jul 2017, Jan Beulich wrote: >>>> Considering the intended purpose here (as far as I recall it), was it >>>> already taken into consideration to request suitable attributes right >>>> at the time the page gets installed into the physmap? Iirc there's no >>>> need to actually "play" with the attributes at random times. >>> >>> This operation would be done before the guest starts. >>> >>> >>> Let's give a look at the list the changes that would be required to make >>> these hypercalls suitable for this task: >>> >>> 1) remove the dependency on CONFIG_HAS_MEM_ACCESS >>> 2) remove the p2m_mem_access_sanity_check check for these two hypercalls >>> 3) remove the (!d->vm_event->monitor.ring_page) check for these two >>> hypercalls >>> 4) prevent p2m->mem_access_enabled from being set for these two hypercalls >>> >>> Am I missing anything? After we do this, would they still be useful for >>> their original mem_access related purpose? >> >> But how would you handle mem_access on those regions in that case? This >> looks completely incompatible. >> >> The memaccess code has to store the previous permission in order to look >> for the fault. Here you want to modify for good. >> >> Furthermore, memaccess is only here to modify permission. It does not >> handle cacheability... So it looks to me you are trying to re-purposing >> an hypercall that will not fit all our needs in the future. >> >> I think the way forward is to introduce an hypercall which populate/map >> memory with a given set of attributes and permissions. >> >> This would simplify quite a lot the logic (one hypercall instead of >> multiple one) and avoid to worry about attributes changed multiple time >> even before the guest is booting. > > Right - that's what I was suggesting with the last paragraph of my > previous reply; I have to admit that I have trouble seeing how > Stefano's response relates to that. I had a hard time interpreting that paragraph. Did you mean: "Have you considered trying to populate the p2m table with the correct permissions when first populating it, rather than populating it with plain rw ram and then changing it afterwards?" -George _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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