linux-kernel - Re: [PATCH v6 0/7] Fix stale IOTLB entries for kernel address space

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Message-ID: <c3eee56a-7fe3-454c-878f-cff37467fb7e@intel.com>
Date: Fri, 17 Oct 2025 10:28:50 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Jason Gunthorpe <jgg@...dia.com>, Baolu Lu <baolu.lu@...ux.intel.com>
Cc: Andrew Morton <akpm@...ux-foundation.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>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, 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>,
 David Hildenbrand <david@...hat.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Michal Hocko <mhocko@...nel.org>, Matthew Wilcox <willy@...radead.org>,
 iommu@...ts.linux.dev, security@...nel.org, x86@...nel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 "Jiang, Dave" <dave.jiang@...el.com>,
 Vinicius Costa Gomes <vinicius.gomes@...el.com>
Subject: Re: [PATCH v6 0/7] Fix stale IOTLB entries for kernel address space

On 10/17/25 07:01, Jason Gunthorpe wrote:
>>> The other alternative is to have arch_vmap_pmd_supported() return false
>>> when SVA is active, or maybe when it's supported on the platform.
>>>
>>> Either of those are 10-ish lines of code and easy to backport.
>> Hi iommu folks, any insights on this?
> IDK, the only SVA user on x86 I know is IDXD, so if you do the above
> plan you break IDXD in all stable kernels. Doesn't sound OK?

Vinicius, any thoughts on this?

I'm thinking that even messing with arch_vmap_pmd_supported() would be
suboptimal. The easiest thing is to just stick the attached patch in
stable kernels and disable SVA at compile time.

There just aren't enough SVA users out in the wild to justify more
complexity than this.
View attachment "svm.patch" of type "text/x-patch" (2868 bytes)