linux-kernel - Re: [PATCH v3 1/1] iommu/sva: Invalidate KVA range on kernel TLB flush

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Message-ID: <d02cb97a-7cea-4ad3-82b3-89754c5278ad@intel.com>
Date: Wed, 6 Aug 2025 09:04:29 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Lu Baolu <baolu.lu@...ux.intel.com>, 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>, Alistair Popple <apopple@...dia.com>,
 Peter Zijlstra <peterz@...radead.org>, Uladzislau Rezki <urezki@...il.com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Andy Lutomirski <luto@...nel.org>, 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 v3 1/1] iommu/sva: Invalidate KVA range on kernel TLB
 flush

On 8/6/25 08:52, Jason Gunthorpe wrote:
>> Isn't that still a use-after-free? It's for some arbitrary amount of
>> time and better than before but it's still a use-after-free.
> Yes it is.
> 
> You can't do this approach without also pushing the pages to freed on
> a list and defering the free till the work. This is broadly what the
> normal mm user flow is doing..

FWIW, I think the simplest way to do this is to plop an unconditional
schedule_work() in pte_free_kernel(). The work function will invalidate
the IOTLBs and then free the page.

Keep the schedule_work() unconditional to keep it simple. The
schedule_work() is way cheaper than all the system-wide TLB invalidation
IPIs that have to get sent as well. No need to add complexity to
optimize out something that's in the noise already.