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

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Message-ID: <20250715122504.GK2067380@nvidia.com>
Date: Tue, 15 Jul 2025 09:25:04 -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 Tue, Jul 15, 2025 at 01:55:01PM +0800, Baolu Lu wrote:
> Yes, the mm (struct mm of processes that are bound to devices) list is
> an unbounded list and can theoretically grow indefinitely. This results
> in an unpredictable critical region.

Every MM has a unique PASID so I don't see how you can avoid this.

> @@ -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.

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.

One of the KPTI options might be easier at that point..

Jason