On Tue, Dec 02, 2014 at 05:06:09PM +0000, Marc Zyngier wrote: > On 02/12/14 16:24, Andre Przywara wrote: > > Hej Christoffer, > > > > On 30/11/14 08:30, Christoffer Dall wrote: > >> On Fri, Nov 28, 2014 at 03:24:11PM +0000, Andre Przywara wrote: > >>> Hej Christoffer, > >>> > >>> On 25/11/14 10:41, Christoffer Dall wrote: > >>>> Hi Andre, > >>>> > >>>> On Mon, Nov 24, 2014 at 04:00:46PM +0000, Andre Przywara wrote: > >>>> > >>> > > > > [...] > > > >>>>>>> + > >>>>>>> + if (!is_in_range(mmio->phys_addr, mmio->len, rdbase, > >>>>>>> + GIC_V3_REDIST_SIZE * nrcpus)) > >>>>>>> + return false; > >>>>>> > >>>>>> Did you think more about the contiguous allocation issue here or can you > >>>>>> give me a pointer to the requirement in the spec? > >>>>> > >>>>> 5.4.1 Re-Distributor Addressing > >>>>> > >>>> > >>>> Section 5.4.1 talks about the pages within a single re-distributor having > >>>> to be contiguous, not all the re-deistributor regions having to be > >>>> contiguous, right? > >>> > >>> Ah yes, you are right. But I still think it does not matter: > >>> 1) We are "implementing" the GICv3. So as the spec does not forbid this, > >>> we just state that the redistributor register maps for each VCPU are > >>> contiguous. Also we create the FDT accordingly. I will add a comment in > >>> the documentation to state this. > >>> > >>> 2) The kernel's GICv3 DT bindings assume this allocation is the default. > >>> Although Marc added bindings to work around this (stride), it seems much > >>> more logical to me to not use it. > >> > >> I don't disagree (and never have) with the fact that it is up to us to > >> decide. > >> > >> My original question, which we haven't talked about yet, is if it is > >> *reasonable* to assume that all re-distributor regions will always be > >> contiguous? > >> > >> How will you handle VCPU hotplug for example? > > > > As kvmtool does not support hotplug, I haven't thought about this yet. > > To me it looks like userland should just use maxcpus for the allocation. > > If I get the current QEMU code right, there is room for 127 GICv3 VCPUs > > (2*64K per VCPU + 64K for the distributor in 16M space) at the moment. > > Kvmtool uses a different mapping, which allows to share 1G with virtio, > > so the limit is around 8000ish VCPUs here. > > Are there any issues with changing the QEMU virt mapping later? > > Migration, maybe? > > If the UART, the RTC and the virtio regions are moved more towards the > > beginning of the 256MB PCI mapping, then there should be space for a bit > > less than 1024 VCPUs, if I get this right. > > > >> Where in the guest > >> physical memory map of our various virt machines should these regions > >> sit so that we can allocate anough re-distributors for VCPUs etc.? > > > > Various? Are there other mappings than those described in hw/arm/virt.c? > > > >> I just want to make sure we're not limiting ourselves by some amount of > >> functionality or ABI (redistributor base addresses) that will be hard to > >> expand in the future. > > > > If we are flexible with the mapping at VM creation time, QEMU could just > > use a mapping depending on max_cpus: > > < 128 VCPUs: use the current mapping > > 128 <= x < 1020: use a more compressed mapping > >> = 1020: map the redistributor somewhere above 4 GB > > > > As the device tree binding for GICv3 just supports a stride value, we > > don't have any other real options beside this, right? So how I see this, > > a contiguous mapping (with possible holes) is the only way. > > Not really. The GICv3 binding definitely supports having several regions > for the redistributors (see the binding documentation). This allows for > the pathological case where you have N regions for N CPUs. Not that we > ever want to go there, really. > What are your thoughts on mapping all of the redistributor regions in one consecutive guest phys address space chunk? Am I making an issue out of nothing? -Christoffer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
