Hi Christoffer, On 04/14/2016 02:04 PM, Christoffer Dall wrote: > On Mon, Apr 04, 2016 at 10:47:30AM +0200, Eric Auger wrote: >> With the advent of GICv3 ITS in-kernel emulation, KVM MSI routing >> becomes mandated for proper VIRTIO-PCI vhost integration. >> >> In QEMU, when the VIRTIO-PCI device is programmed with the MSI message, >> we previously used direct_mapping trick: this consists in extracting the >> SPI ID found in the MSI message and associating an irqfd to that SPI ID. >> When vhost worker thread gets a new buffer it signals the irqfd and kvm >> then injects this SPI ID on guest. That way although the guest uses MSIs, >> no MSI emulation is used. >> >> This worked fine with GICv2m but does not work anymore with GICV3 ITS. >> Indeed this latter implements IRQ translation: what is found in the MSI >> message no more is the target SPI ID but is an intermediate event ID used >> in the translation process. >> >> Hence true MSI routing is needed so that the vhost back channel irqfd is >> associated to a dummy gsi ID, routed towards the programmed MSI. When KVM > > Doesn't the guest have to program the device with some ID? So how is > this dummy GSI ID assigned? Please apologize for the delay. We have this path: irqfd -> dummy GSI -> MSI -> LPI ID the MSI route does the link between the dummy GSI and the MSI. the device id is embedded in the route entry definition (devid field of kvm_irq_routing_msi) The eventid is put in the MSI data see https://lists.gnu.org/archive/html/qemu-devel/2015-11/msg06178.html (Pavel's vITS RFC) in QEMU, kvm-all.c/kvm_irqchip_add_msi_route allocates the "dummy" gsi (kvm_irqchip_get_virq) and builds the routing entry. > >> injects the MSI through the in-kernel ITS emulation, the MSI is properly >> translated and eventually the SPI ID associated to the event ID is injected >> on guest. > > Isn't it an LPI that is injected to the guest when you have an emulated > ITS then? It is definitively an LPI ID. > >> >> irqchip routing does not sound to be really useful on arm but usage of > > Is this also true if you had multiple emulated ITS devices? > > (I just don't want to block our options of doing this in the future if > ever required.) yes irqchip routing may be useful to handle multiple guest irqchips. I meant: currently irqchip routing comes with this series although this is not the series' primary goal. There is no special limitation except it does not apply to KVM_IRQ_LINE ioctl because of the gsi semantic chosen in the past, for ARM: bits: | 31 ... 24 | 23 ... 16 | 15 ... 0 | field: | irq_type | vcpu_index | irq_id | Best Regards Eric > >> MSI routing also mandates to integrate irqchip routing. The initial >> implementation of irqfd on arm must be upgraded with the integration >> of kvm irqchip.c code and the implementation of its standard hooks >> in the architecture specific part. >> >> In case KVM_SET_GSI_ROUTING ioctl is not called, a default routing >> table with flat irqchip routing entries is built enabling to inject gsi >> corresponding to the SPI indexes seen by the guest. >> >> As soon as KVM_SET_GSI_ROUTING is called, user-space overwrites this >> default routing table and is responsible for building the whole routing >> table. >> >> for arm/arm64 KVM_SET_GSI_ROUTING has a limited support: >> - only applies to KVM_IRQFD and not to KVM_IRQ_LINE >> >> - irqchip routing was tested on Calxeda midway (VFIO with irqfd) >> with and without explicit routing >> - MSI routing without GICv3 ITS was tested using APM Xgene-I >> (qemu VIRTIO-PCI vhost-net without gsi_direct_mapping). >> - MSI routing with GICv3 ITS is *NOT* tested. >> >> Code can be found at https://git.linaro.org/people/eric.auger/linux.git/shortlog/refs/heads/v4.5-rc6-its-emul-v4-gsi-routing-v4 >> >> The series applies on top of Andre's branch featuring NEW-VGIC and in-kernel >> ITS emulation series: >> http://www.linux-arm.org/git?p=linux-ap.git;a=log;h=refs/heads/its-emul/v4 >> >> [1]: [PATCH v4 00/12] KVM: arm64: GICv3 ITS emulation >> http://www.spinics.net/lists/arm-kernel/msg492770.html >> [2]: [RFC PATCH 00/45] KVM: arm/arm64: Rework virtual GIC emulation >> http://www.spinics.net/lists/arm-kernel/msg492639.html >> >> GSI flat routing setup on QEMU can be found at: >> https://lists.nongnu.org/archive/html/qemu-devel/2015-07/msg06262.html >> >> History: >> v3 -> v4: >> - rebase on top of NEW-VGIC RFC and ITS emulation series v4. This is not >> a stable foundation yet. Hence the revert to RFC. This v4 mostly is a >> reflesh/reminder. >> - rewrite the cover letter >> >> v2 -> v3: >> - don't use KVM_IRQ_ROUTING_EXTENDED_MSI type at uapi and kernel level anymore; >> use KVM_MSI_VALID_DEVID flag instead >> - propagate user flags downto the kernel to make sure the userspace >> correctly set devid in GICv3 ITS case (still under discussion) >> >> v1 -> v2: >> - user API changed: >> x devid id passed in kvm_irq_routing_msi >> x kept the new routing entry type: KVM_IRQ_ROUTING_EXTENDED_MSI >> - kvm_host.h: adopt Andre's proposal to replace the msi_msg by a struct >> composed of the msi_msg and devid in kvm_kernel_irq_routing_entry >> - Fix bug reported by Pavel: Added KVM_IRQ_ROUTING_EXTENDED_MSI handling >> in eventfd.c >> - added vgic_v2m_inject_msi in vgic-v2-emul.c as suggested by Andre >> - fix bug reported by Andre: bad setting of msi.flags and msi.devid >> in kvm_send_userspace_msi >> - avoid injecting reserved IRQ numbers in vgic_irqfd_set_irq >> >> RFC -> PATCH: >> - clearly state limited support on arm/arm64: >> KVM_IRQ_LINE not impacted by GSI routing >> - add default routing table feature (new patch file) >> - changed uapi to use padding field area >> - reword api.txt >> >> >> >> Eric Auger (7): >> KVM: api: pass the devid in the msi routing entry >> KVM: kvm_host: add devid in kvm_kernel_irq_routing_entry >> KVM: irqchip: convey devid to kvm_set_msi >> KVM: arm/arm64: enable irqchip routing >> KVM: arm/arm64: build a default routing table >> KVM: arm/arm64: enable MSI routing >> KVM: arm: enable KVM_SIGNAL_MSI and MSI routing >> >> Documentation/virtual/kvm/api.txt | 35 ++++++++++++--- >> arch/arm/include/asm/kvm_host.h | 2 + >> arch/arm/kvm/Kconfig | 3 ++ >> arch/arm/kvm/Makefile | 1 + >> arch/arm64/include/asm/kvm_host.h | 1 + >> arch/arm64/kvm/Kconfig | 3 ++ >> arch/arm64/kvm/Makefile | 1 + >> include/kvm/vgic/vgic.h | 2 - >> include/linux/kvm_host.h | 8 +++- >> include/uapi/linux/kvm.h | 5 ++- >> virt/kvm/arm/vgic/vgic-v2.c | 15 +++++++ >> virt/kvm/arm/vgic/vgic.c | 7 --- >> virt/kvm/arm/vgic/vgic.h | 1 + >> virt/kvm/arm/vgic/vgic_init.c | 24 +++++++++++ >> virt/kvm/arm/vgic/vgic_irqfd.c | 91 +++++++++++++++++++++++++++++++-------- >> virt/kvm/irqchip.c | 8 +++- >> 16 files changed, 170 insertions(+), 37 deletions(-) >> >> -- >> 1.9.1 >> -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
