linux-kernel - Re: [PATCH v2 1/1] iommu/sva: Invalidate KVA range on kernel TLB flush

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Message-ID: <20250716120817.GY2067380@nvidia.com>
Date: Wed, 16 Jul 2025 09:08:17 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
	Kevin Tian <kevin.tian@...el.com>, Jann Horn <jannh@...gle.com>,
	Vasant Hegde <vasant.hegde@....com>,
	Dave Hansen <dave.hansen@...el.com>,
	Alistair Popple <apopple@...dia.com>,
	Uladzislau Rezki <urezki@...il.com>,
	Jean-Philippe Brucker <jean-philippe@...aro.org>,
	Andy Lutomirski <luto@...nel.org>,
	"Tested-by : Yi Lai" <yi1.lai@...el.com>, iommu@...ts.linux.dev,
	security@...nel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH v2 1/1] iommu/sva: Invalidate KVA range on kernel TLB
 flush

On Wed, Jul 16, 2025 at 02:34:04PM +0800, Baolu Lu wrote:
> > > @@ -654,6 +656,9 @@ struct iommu_ops {
> > > 
> > >   	int (*def_domain_type)(struct device *dev);
> > > 
> > > +	void (*paging_cache_invalidate)(struct iommu_device *dev,
> > > +					unsigned long start, unsigned long end);
> > 
> > How would you even implement this in a driver?
> > 
> > You either flush the whole iommu, in which case who needs a rage, or
> > the driver has to iterate over the PASID list, in which case it
> > doesn't really improve the situation.
> 
> The Intel iommu driver supports flushing all SVA PASIDs with a single
> request in the invalidation queue.

How? All PASID !=0 ? The HW has no notion about a SVA PASID vs no-SVA
else. This is just flushing almost everything.

> > If this is a concern I think the better answer is to do a defered free
> > like the mm can sometimes do where we thread the page tables onto a
> > linked list, flush the CPU cache and push it all into a work which
> > will do the iommu flush before actually freeing the memory.
> 
> Is it a workable solution to use schedule_work() to queue the KVA cache
> invalidation as a work item in the system workqueue? By doing so, we
> wouldn't need the spinlock to protect the list anymore.

Maybe.

MM is also more careful to pull the invalidation out some of the
locks, I don't know what the KVA side is like..

Jason