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malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2505160000 definitions=main-2507140104 X-Proofpoint-ORIG-GUID: LLv66cv_FE7y2uBJj5dg20ng_M4xVVxa X-Authority-Analysis: v=2.4 cv=Of+YDgTY c=1 sm=1 tr=0 ts=68753592 cx=c_pps a=OOZaFjgC48PWsiFpTAqLcw==:117 a=OOZaFjgC48PWsiFpTAqLcw==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=Wb1JkmetP80A:10 a=GoEa3M9JfhUA:10 a=Je24I9W20XTlM0MTOr0A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: LLv66cv_FE7y2uBJj5dg20ng_M4xVVxa X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNzE0MDEwNCBTYWx0ZWRfX6upKue2nu+vx i/oBTP/RH5FX6+wkPWCOZ1It0avf4uMpCzfo90h4OxofQbE9C6mBiXvD7AhnYLNmFrajB0rDwLP l3G+yE50vCUtphaZ8dNTqvBaUfZkEfxS/fKPM3LmFDsh0bz3mZ72sKNhzVsDDL/TTeZvc3WjGbk 7Shuvi0carTRI0dLrT9Ykk0+/zyVlRlGgwiSjUo/PWq4MRYoHA/o6u1izhA1kTRml1n79dH5HzF kctqSRBe2PKb1tPRvkWztU/FFHvMq30uiiUsM3ve5JzBQtJcFrIaSq3hXvMDNsB21yBQOnYN+vl EDauatacCFQ0JoV2uPSRb5pTm7f3RXJjzqDk4dx6uemqYiie3vSvWy8p9MFVQ8mxmCd54qcUxiG 6Z/6Rn9NgFPrPO+/kYOLn2b4F/vnxFvZCfH+k2sMX4eIqTd6znFCWc9OUxQ0ATeLiuwQeKWd On 7/2/2025 11:19 AM, Oliver Upton wrote: > On Wed, Jul 02, 2025 at 07:41:37AM -0700, Steve Sistare wrote: >> When kvm_irqfd_deassign ... -> kvm_vgic_v4_unset_forwarding is called, >> if an interrupt is pending in irq->pending_latch, then transfer it to >> the producer's eventfd. This way, if the KVM instance is subsequently >> destroyed, the interrupt is preserved in producer state. If the irqfd >> is re-created in a new KVM instance, kvm_irqfd_assign finds the producer, >> polls the eventfd, finds the interrupt, and injects it into KVM. >> >> QEMU live update does that: it passes the VFIO device descriptors to the >> new process, but destroys and recreates the KVM instance, without >> quiescing VFIO interrupts. > > This *does not work*. Updates to the ITS mapping are non-atomic and a > poorly timed MSI will get dropped on the floor. Or generate an SError if > your system implementer has a sense of humor. > > KVM already provides the SAVE_PENDING_TABLES ioctl for saving the > pending state of LPIs to memory which also retrieves the pending state > of vLPIs from hardware. The expectation for this ioctl is that userspace > has already quiesced the interrupt generator. Thank you Oliver for reviewing this and suggesting SAVE_PENDING_TABLES. I have added it to the QEMU live update sequence, after calling kvm_irqfd_deassign, and it does the trick. - Steve > If userspace can't honor that I don't see a reason for KVM to go out of > the way to forward the pending state, especially considering the fact > that the architecture doesn't support this behavior. > > A spurious interrupt doesn't seem that bad here. > >> -int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int host_irq) >> +int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int host_irq, bool *pending) >> { >> struct vgic_irq *irq; >> unsigned long flags; >> int ret = 0; >> + bool direct_msi = vgic_supports_direct_msis(kvm); >> >> - if (!vgic_supports_direct_msis(kvm)) >> + if (!pending && !direct_msi) >> return 0; > > You've broken the early return in case hardware doesn't support GICv4... > >> irq = __vgic_host_irq_get_vlpi(kvm, host_irq); >> @@ -542,7 +543,13 @@ int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int host_irq) >> >> raw_spin_lock_irqsave(&irq->irq_lock, flags); >> WARN_ON(irq->hw && irq->host_irq != host_irq); >> - if (irq->hw) { >> + >> + if (pending) { >> + *pending = irq->pending_latch; >> + irq->pending_latch = false; >> + } >> + > > So this "works" for software-injected LPIs (notice that this function is > for handling *vLPIs*) as KVM's pending state is always the source of > truth. Is that why you're allowing GICv3 to get here now? > > This (importantly) doesn't work for hardware vLPIs, as the pending state > is maintained in the vLPI pending table for the vPE. > > Overall, I'm not convinced KVM needs to do anything here. We have state > save/restore mechanisms readily available, if userspace wants to go > off-label then it's up to userspace to figure that out. > > Thanks, > Oliver