From: Maxim Levitsky Date: Wed, 11 Jun 2025 22:45:21 +0000 (-0700) Subject: KVM: SVM: Disable (x2)AVIC IPI virtualization if CPU has erratum #1235 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8de4a1c8164e5b2e40d1df764840a31de983f40b;p=thirdparty%2Fkernel%2Fstable.git KVM: SVM: Disable (x2)AVIC IPI virtualization if CPU has erratum #1235 Disable IPI virtualization on AMD Family 17h CPUs (Zen2 and Zen1), as hardware doesn't reliably detect changes to the 'IsRunning' bit during ICR write emulation, and might fail to VM-Exit on the sending vCPU, if IsRunning was recently cleared. The absence of the VM-Exit leads to KVM not waking (or triggering nested VM-Exit of) the target vCPU(s) of the IPI, which can lead to hung vCPUs, unbounded delays in L2 execution, etc. To workaround the erratum, simply disable IPI virtualization, which prevents KVM from setting IsRunning and thus eliminates the race where hardware sees a stale IsRunning=1. As a result, all ICR writes (except when "Self" shorthand is used) will VM-Exit and therefore be correctly emulated by KVM. Disabling IPI virtualization does carry a performance penalty, but benchmarkng shows that enabling AVIC without IPI virtualization is still much better than not using AVIC at all, because AVIC still accelerates posted interrupts and the receiving end of the IPIs. Note, when virtualizing Self-IPIs, the CPU skips reading the physical ID table and updates the vIRR directly (because the vCPU is by definition actively running), i.e. Self-IPI isn't susceptible to the erratum *and* is still accelerated by hardware. Signed-off-by: Maxim Levitsky [sean: rebase, massage changelog, disallow user override] Acked-by: Naveen N Rao (AMD) Link: https://lore.kernel.org/r/20250611224604.313496-20-seanjc@google.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c index d0b845ab66fe..72b8cab2fbce 100644 --- a/arch/x86/kvm/svm/avic.c +++ b/arch/x86/kvm/svm/avic.c @@ -1188,6 +1188,14 @@ bool avic_hardware_setup(void) if (x2avic_enabled) pr_info("x2AVIC enabled\n"); + /* + * Disable IPI virtualization for AMD Family 17h CPUs (Zen1 and Zen2) + * due to erratum 1235, which results in missed VM-Exits on the sender + * and thus missed wake events for blocking vCPUs due to the CPU + * failing to see a software update to clear IsRunning. + */ + enable_ipiv = enable_ipiv && boot_cpu_data.x86 != 0x17; + amd_iommu_register_ga_log_notifier(&avic_ga_log_notifier); return true;