Hello! I'd like to remind that this will break with current vITS code and VFIO. The problem is short path for raising MSIs via routed GSI. There is a code which directly calls IRQ injection instead of triggering irqfd. With VFIO this code is called from within interrupt context. This will cause random lockups in vits_inject_msi(), which does not use irq-save spin-locking. I hit this several times and I had to rework ITS emulation in my local tree. Kind regards, Pavel Fedin Senior Engineer Samsung Electronics Research center Russia -----Original Message----- From: Eric Auger [mailto:eric.auger@xxxxxxxxxx] Sent: Monday, April 04, 2016 11:48 AM To: eric.auger@xxxxxx; eric.auger@xxxxxxxxxx; christoffer.dall@xxxxxxxxxx; marc.zyngier@xxxxxxx; andre.przywara@xxxxxxx; kvmarm@xxxxxxxxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx Cc: patches@xxxxxxxxxx; pbonzini@xxxxxxxxxx; p.fedin@xxxxxxxxxxx; Manish.Jaggi@xxxxxxxxxxxxxxxxxx Subject: [RFC v4 0/7] KVM: arm/arm64: gsi routing support 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 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. irqchip routing does not sound to be really useful on arm but usage of 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
