Re: [PATCH] KVM: SVM: Disable AVIC IPI virtualization on Hygon Family 18h (erratum #1235)

[Sean Christopherson <seanjc@google.com>]

On Fri, May 22, 2026, Tina Zhang wrote:
> Hygon Family 18h CPUs are derived from AMD Family 17h (Zen1) silicon and
> share the same erratum #1235: hardware may read a stale IsRunning=1 bit
> during ICR write emulation and silently fail to generate an
> AVIC_IPI_FAILURE_TARGET_NOT_RUNNING VM-Exit on the sending vCPU.
> 
> The absence of the VM-Exit causes KVM to miss the required wakeup of
> blocking target vCPUs, leading to hung vCPUs and unbounded delays in
> guest execution.
> 
> Extend the existing AMD Family 17h erratum #1235 workaround to also cover
> Hygon Family 18h.  With IPI virtualization disabled, KVM never sets
> IsRunning=1 in the Physical ID table, so every non-self IPI generates a
> VM-Exit and is correctly emulated.
> 
> Fixes: 8de4a1c8164e ("KVM: SVM: Disable (x2)AVIC IPI virtualization if CPU has erratum #1235")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Tina Zhang <zhang_wei@open-hieco.net>
> ---
>  arch/x86/kvm/svm/avic.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index adf211860949..993b551180fe 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -1300,12 +1300,14 @@ bool __init avic_hardware_setup(void)
>  	}
>  
>  	/*
> -	 * 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.
> +	 * Disable IPI virtualization for AMD Family 17h (Zen1 and Zen2) and
> +	 * Hygon Family 18h (derived from AMD Zen1) CPUs 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;
> +	if (boot_cpu_data.x86 == 0x17 || boot_cpu_data.x86 == 0x18)

IIUC, family 18h is carved out entirely for Hygon, correct?  I.e. there's no risk
of disabling IPI virtualization on unaffected AMD CPUs?

> +		enable_ipiv = false;
>  
>  	amd_iommu_register_ga_log_notifier(&avic_ga_log_notifier);
>  
> -- 
> 2.43.7
>