On Mon, Jan 12, 2015 at 12:33:26PM +0000, Andre Przywara wrote: > Hej Christoffer, > > On 11/01/15 15:22, Christoffer Dall wrote: > > On Fri, Jan 09, 2015 at 01:42:42PM +0000, Andre Przywara wrote: > >> Hi Christoffer, > >> > >> On 09/01/15 12:33, Christoffer Dall wrote: > >>> On Fri, Jan 09, 2015 at 11:54:36AM +0000, Andre Przywara wrote: > >>>> While we can easily register and unregister KVM devices, there is > >>>> currently no easy way of checking whether a device has been > >>>> registered. > >>>> Introduce kvm_check_device_type() for that purpose and use it in two > >>>> existing functions. Also change the return code for an invalid > >>>> type number from ENOSPC to EINVAL. > >>>> This function will be later used by another patch set to check > >>>> whether a KVM_CREATE_IRQCHIP ioctl is valid. > >>> > >>> I feel like this is misguided and the vgic should be able to figure this > >>> stuff out internally. Did you have code for this approach somewhere > >>> that I can take a look at? > >> > >> I pushed my WIP patch on top of the kvm-gicv3/v6 tree. > >> Given how that looks I reckoned the generic solution would be more > >> preferable. > >> Basically we internally decide in the _probe function whether we support > >> GICv2 emulation or not, which is mostly driven by device tree > >> properties. So at the moment I just register the GIC_V2 KVM device or > >> not. Now with the "vgic internal" solution I misuse the GICV address > >> base as a hint of the GICv2 emulation availability. Alternatively I have > >> to introduce a new variable to mirror what the KVM device array already > >> holds, which seems kind of exerted to me. > >> Besides that I am not sure if the GICV address hint will always be a > >> reliable indicator and what we will do if there will be another GIC > >> model to be emulated in the future (maybe we need that for the ITS > >> emulation already?) > > > > I don't think it looks that bad. > > > > Only your gicv3 and gicv2 code files know what they are capable of > > emulating, how you choose to store this state internally in those files > > is a somewhat orthogonal discussion from using the kvm device API. > > Well, the point is that the emulation capability is a hardware property > and thus the knowledge is actually in the host part of the VGIC (so in > vgic-v3.c and vgic-v2.c). From here we "communicate" the capability to > userland by registering the respective VGIC KVM devices only. Since the > emulation part of the VGIC lives in different files (vgic.c and > vgic-vx-emul.c) we would need some kind of export to them, too. I found > that it would be cleaner to just re-use what we already have with the > KVM devices. > > > Using the KVM device api is just another way of storing and exposing the > > information globally (you take registering the device types as an > > indication of the state). > > > > Finally, I don't even think you ned the can_emulate function, I think > > you should just return an error from init_vgic_model (which happens to > > collide with my suggestion on making those functions a void function in > > one of the previous patches) and you're done. > > I think I checked this before and since the init_vgic_model() > implementations are in vgic-vx-emul.c we don't know the hardware > capability anymore and would need some kind of variable holding that > information (which lead me to re-using the KVM device knowledge). But I > will re-check if there is an easy fix in here. > > >> > >> So I prefer the more generic solution. > >> Let me know what you think, I can as well drop 18/20 and merge the above > >> mentioned patch. > >> > >>> I forget: Are we still requiring KVM_CREATE_IRQCHIP for VGICv3 or are we > >>> just relying on users to use KVM_CREATE_DEVICE for anything in the > >>> future? > >> > >> Since KVM_CREATE_IRQCHIP does not take an argument, we cannot use it for > >> GICv3. So GICv3 mandates KVM_CREATE_DEVICE. We need userspace > >> adjustments for GICv3 anyway, so that's not a problem. > > > > ok, so KVM_CREATE_IRQCHIP is a direct alias for KVM_CREATE_DEVICE(GIC_V2) > > and is deprecated for GICv3? If so, we should probably update the > > documentation to indicate the KVM_CREATE_IRQCHIP creates a GICv2 and > > should not be used for any other in-kernel GIC versions. > > What about the following wording in api.txt: > ----- > On ARM/arm64, a GICv2 is created. Any other VGIC versions require the > usage of KVM_CREATE_DEVICE (which can and should also be used to create > a virtual GICv2). > ----- I would change the parenthesis into something like: ", which also supports creating a GICv2. Using KVM_CREATE_DEVICE is preferred over KVM_CREATE_IRQCHIP for GICv2. > > In fact both QEMU and kvmtool currently try KVM_CREATE_DEVICE first even > for a VGICv2 on a GICv2 and only fall back to KVM_CREATE_IRQCHIP if that > fails (to support older kernels). > Yes, but I think we have older user space (at least QEMU) which we can't quite ignore which expects that KVM_CREATE_IRQCHIP will work. Thanks, -Christoffer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
