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

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Message-ID: <aOVT4VlumG01X0Hk@google.com>
Date: Tue, 7 Oct 2025 10:54:41 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Hou Wenlong <houwenlong.hwl@...group.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 Thu, Sep 18, 2025, Hou Wenlong wrote:
> 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?

Huh.  I completely forgot to send (or even write?) the patch.  I'll send one
shortly.

Thanks much!