linux-kernel - Re: [PATCH] iommu/amd: Ensure GA log notifier callbacks finish running before module unload

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Message-ID: <20250918130320.GA119526@k08j02272.eu95sqa>
Date: Thu, 18 Sep 2025 21:03:20 +0800
From: Hou Wenlong <houwenlong.hwl@...group.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Joerg Roedel <joro@...tes.org>, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/amd: Ensure GA log notifier callbacks finish
 running before module unload

On Fri, Mar 14, 2025 at 08:10:48PM -0700, Sean Christopherson wrote:
> Synchronize RCU when unregistering KVM's GA log notifier to ensure all
> in-flight interrupt handlers complete before KVM-the module is unloaded.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  drivers/iommu/amd/iommu.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index b48a72bd7b23..b314523d9194 100644
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -982,6 +982,14 @@ int amd_iommu_register_ga_log_notifier(int (*notifier)(u32))
>  {
>  	iommu_ga_log_notifier = notifier;
>  
> +	/*
> +	 * Ensure all in-flight IRQ handlers run to completion before returning
> +	 * to the caller, e.g. to ensure module code isn't unloaded while it's
> +	 * being executed in the IRQ handler.
> +	 */
> +	if (!notifier)
> +		synchronize_rcu();
> +
>  	return 0;
>  }
>  EXPORT_SYMBOL(amd_iommu_register_ga_log_notifier);
> 
> base-commit: ea9bd29a9c0d757b3384ae3e633e6bbaddf00725
> -- 
> 2.49.0.rc1.451.g8f38331e32-goog
> 
>
Hi Sean,

Sorry to bother you. I'm reworking the hardware_setup() path in our
internal multi-KVM, but I didn't see any usage of
'amd_iommu_register_ga_log_notifier(NULL)' in the KVM code for now. Has
it not been committed?

Thanks!