From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-comment-return-623-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis.ws5.connectedcommunity.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 730F99860B2 for ; Fri, 15 Feb 2019 12:59:27 +0000 (UTC) References: <20190111114200.10026-2-dgilbert@redhat.com> <20190111131540.12a8abca.cohuck@redhat.com> <20190111122654.GE2738@work-vm> <20190115111038.6769d292.cohuck@redhat.com> <20190115112303.GB2135@work-vm> <20190116115638.152d6797.cohuck@redhat.com> <20190116200625.GG2351@work-vm> <20190211225225.7c39154d.cohuck@redhat.com> <20190213183755.GF2601@work-vm> <20190214115807.2bab4efb.cohuck@redhat.com> <20190214163707.GE2617@work-vm> <20190215120718.7c7e09cc.cohuck@redhat.com> <20190215132843.65552e44.cohuck@redhat.com> <4c526716-44f5-5eea-a855-f0b9f91cb579@redhat.com> <20190215133753.1e74c6d8.cohuck@redhat.com> From: David Hildenbrand Message-ID: <0e4f4c4a-1b32-0dda-1d0f-f5872b68e4db@redhat.com> Date: Fri, 15 Feb 2019 13:59:20 +0100 MIME-Version: 1.0 In-Reply-To: <20190215133753.1e74c6d8.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [virtio-comment] [PATCH 1/3] shared memory: Define shared memory regions To: Cornelia Huck Cc: Frank Yang , "Dr. David Alan Gilbert" , virtio-comment@lists.oasis-open.org, Stefan Hajnoczi , Halil Pasic List-ID: On 15.02.19 13:37, Cornelia Huck wrote: > On Fri, 15 Feb 2019 13:33:06 +0100 > David Hildenbrand wrote: > >> On 15.02.19 13:28, Cornelia Huck wrote: >>> On Fri, 15 Feb 2019 12:26:00 +0100 >>> David Hildenbrand wrote: >>> >>>> Probing is always ugly. But I think we can add something like >>>> the x86 PCI hole between 3 and 4 GB after our initial boot memory. >>>> So there, we would have a memory region just like e.g. x86 has. >>> >>> A special region is probably the best way out of this pickle. We would >>> only need the discovery ccw for virtio, then. >>> >>>> >>>> This should even work with other mechanism I am working on. E.g. >>>> for memory devices, we will add yet another memory region above >>>> the special PCI region. >>>> >>>> The layout of the guest would then be something like >>>> >>>> [0x000000000000000] >>>> ... Memory region containing RAM >>>> [ram_size ] >>>> ... Memory region for e.g. special PCI devices >>>> [ram_size +1 GB ] >>>> ... Memory region for memory devices (virtio-pmem, virtio-mem ...) >>>> [maxram_size - ram_size + 1GB] >>>> >>>> We would have to create proper page tables for guest backing that take >>>> care of the new guest size (not just ram_size). Also, to the guest we >>>> would indicate "maximum ram size == ram_size" so it does not try to >>>> probe the "special" memory. >>> >>> Hm... so that would be: >>> - 0..ram_size: just like it is handled now >>> - ram_size..ram_size + 1GB: guest does not treat it as ram, but does >>> build page tables for it >>> - ram_size + 1GB..maxram_size: for whatever memory devices do with it >>> >>> How does the guest probe this? (SCLP?) Or does the guest simply know >>> via some kind of probable feature that there's a 1GB region there? >> >> As the guest only "knowns" ram, there is a "maximum ram size" specified >> via SCLP. An unmodified guest will not probe beyond that. > > Nod. > >> The parts of the 1GB used by a device should be communicated via the >> paravirtualized device I guess. PCI bars don't really fit I assume, so >> we might need some virtio-ccw thingy (you're the expert :)) on top. That >> is one part to be clarified. >> >> I guess the guest does not need to know about the whole 1GB, only per >> device about the used part. We can then built page tables in the guest >> for that part when plugging. > > Hm. With my proposal, the guest would get a list of region addresses > from the device via a new ccw. It could then proceed to set up page > tables for it and start to use it. As long as it is aware that the > addresses it will get are beyond max_ram, that should be fine, I think. > Sounds like this could work in general. -- Thanks, David / dhildenb This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/