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

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Message-ID: <20251017140101.GM3901471@nvidia.com>
Date: Fri, 17 Oct 2025 11:01:02 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>
Cc: Dave Hansen <dave.hansen@...el.com>,
	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
Subject: Re: [PATCH v6 0/7] Fix stale IOTLB entries for kernel address space

On Fri, Oct 17, 2025 at 09:42:10AM +0800, Baolu Lu wrote:
> On 10/15/25 23:55, Dave Hansen wrote:
> > > > Only [7/7] has acc:stable, even though that patch is not at all
> > > > backportable.  Please give some thought and suggestions regarding
> > > > whether you think we should backport this into earlier kernels.
> > > Yes. We should backport this series to stable kernels.
> > > 
> > > > If "yes" then the size and scope of the series looks problematic.  Is
> > > > it possible to put together something simple and expedient just to plug
> > > > the hole in older kernels?
> > > Squashing some patches is one way. But would it be workable to backport
> > > this series manually? Say, could we send a pull request to the stable
> > > mailing list after this series has landed?
> > I honestly think we should just disable SVA in old kernels at compile
> > time, or at least default it to be disabled at runtime. That's the
> > simplest thing.
> > 
> > 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?

Jason