[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]
Subject: Re: [virtio-comment] [PATCH 1/3] shared memory: Define shared memory regions
On 15.02.19 13:37, Cornelia Huck wrote: > On Fri, 15 Feb 2019 13:33:06 +0100 > David Hildenbrand <david@redhat.com> wrote: > >> On 15.02.19 13:28, Cornelia Huck wrote: >>> On Fri, 15 Feb 2019 12:26:00 +0100 >>> David Hildenbrand <david@redhat.com> 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
[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]