Re: [PATCH v7 00/17] KVM: arm64: GICv3 ITS emulation

[Andre Przywara <andre.przywara@arm.com>]

Hi,

On 29/06/16 05:43, Bharat Bhushan wrote:
> 
> 
>> -----Original Message-----
>> From: kvmarm-bounces@lists.cs.columbia.edu [mailto:kvmarm-
>> bounces@lists.cs.columbia.edu] On Behalf Of Andre Przywara
>> Sent: Tuesday, June 28, 2016 6:02 PM
>> To: Marc Zyngier <marc.zyngier@arm.com>; Christoffer Dall
>> <christoffer.dall@linaro.org>; Eric Auger <eric.auger@redhat.com>
>> Cc: linux-arm-kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu;
>> kvm@vger.kernel.org
>> Subject: [PATCH v7 00/17] KVM: arm64: GICv3 ITS emulation
>>
>> Hi,
>>
>> another try on the KVM ITS emulation support.
>> It allows those KVM guests that use an emulated GICv3 to use LPIs as well,
>> though in the moment this is limited to emulated PCI devices.
>> This is based on kvm-arm-for-v4.7-rc2 and relies on the new VGIC
>> implementation.
>>
>> Compared to the last drop there have been some changes to the code:
>> The reference counting has been rewritten to use the kref infrastructure.
>> This has some implications on the rest of the code, for instance the locking
>> for the LPI list got changed. There is no RCU usage anymore, instead the LPI
>> list is now protected by a spinlock. To overcome the problem where we need
>> to access guest memory while holding the lock, we create a snapshot of the
>> LPI list, so we can iterate over LPIs with the lock dropped.
>> Also the base register sanitisation has been reworked completely, which
>> includes some changes to the arm-gic-v3.h header file (as a separate patch
>> 07/17). I hope I covered all the subtleties of those bits.
>> Also the MMIO framework saw some changes, we now tag the different GIC
>> regions explicitly and are able to call the different handlers explicitly.
>> Also Patch 05/17 extends the kvm-io-bus framework with a small function to
>> get the kvm_io_device structure for a given MMIO address. This allows us to
>> keep the knowledge of all the ITSes in this framework, but still get the
>> respective ITS pointer easily without reverting to "fake" MMIO accesses.
>> Also all the smaller review comments have been addressed.
>>
>> You can find all of this code (and the prerequisites) in the
>> its-emul/v7 branch of my repository [1].
>> This has been briefly tested on the model and on GICv3 hardware.
>> If you have GICv3 capable hardware, please test it on your setup.
> 
> We have GICv3 capable hardware and we can test these on that.
> How you are testing these changes? QEMU side changes are also required, can you share those changes?

I don't have any QEMU patches, that is on Linaro's plate, as far as I
can tell. I don't know what the status is there. For real patches we
would need to agree on the userland interface, I guess.
However hacking something in QEMU shouldn't be too hard, you basically
have to inject the ITS DT node and reserve some space in the memory map.
Then tell QEMU to use KVM_SIGNAL_MSI to trigger IRQs.
You can look at the kvmtool patches to get an idea on what to cover.

Further below I gave some hints on testing this series with kvmtool.

....

>>
>> For the time being this series gives us the ability to use emulated PCI devices
>> that can use MSIs in the guest. Those have to be triggered by letting the
>> userland device emulation simulate the MSI write with the
>> KVM_SIGNAL_MSI ioctl. This will be translated into the proper LPI by the ITS
>> emulation and injected into the guest in the usual way (just with a higher IRQ
>> number).
>>
>> This series is based on kvm-arm-for-v4.7-rc2 and can be found at the
>> its-emul/v7 branch of this repository [1].
>> For this to be used you need a GICv3 host machine (a fast model would do),
>> though it does not rely on any host ITS bits (neither in hardware or software).
>>
>> To test this you can use the kvmtool patches available in the "its-v6"
>> branch here [2].
>> Start a guest with: "$ lkvm run --irqchip=gicv3-its --force-pci"
>> and see the ITS being used for instance by the virtio devices.

^^^^ here you go.

Cheers,
Andre.

>>
>> [1]: git://linux-arm.org/linux-ap.git
>>      http://www.linux-arm.org/git?p=linux-ap.git;a=log;h=refs/heads/its-
>> emul/v7
>> [2]: git://linux-arm.org/kvmtool.git
>>      http://www.linux-arm.org/git?p=kvmtool.git;a=log;h=refs/heads/its-v6
>> [3]:
>> http://arminfo.emea.arm.com/help/topic/com.arm.doc.ihi0069a/IHI0069A_g
>> ic_architecture_specification.pdf
>>