linux-kernel - Re: [PATCH v4] io: add io

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Message-ID: <20251219162734.46f3aa9d@fedora>
Date: Fri, 19 Dec 2025 16:27:34 +0100
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Alice Ryhl <aliceryhl@...gle.com>, Miguel Ojeda <ojeda@...nel.org>, Will
 Deacon <will@...nel.org>, Daniel Almeida <daniel.almeida@...labora.com>,
 Robin Murphy <robin.murphy@....com>, Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, Andreas
 Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, Danilo
 Krummrich <dakr@...nel.org>, Joerg Roedel <joro@...tes.org>, Lorenzo
 Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett"
 <Liam.Howlett@...cle.com>, Asahi Lina <lina+kernel@...hilina.net>,
 linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
 iommu@...ts.linux.dev, linux-mm@...ck.org
Subject: Re: [PATCH v4] io: add io_pgtable abstraction

On Fri, 19 Dec 2025 11:14:34 -0400
Jason Gunthorpe <jgg@...pe.ca> wrote:

> On Fri, Dec 19, 2025 at 04:11:53PM +0100, Boris Brezillon wrote:
> 
> > There's actually a confusion between TLB invalidation and L1/L2 cache
> > flush/invalidation. The things we can decide to flush/invalidate around
> > map/unmap ops are L1/L2 caches. The TLB invalidate, we don't have
> > direct control on: it happens as part of the LOCK+UNLOCK sequence, and
> > no matter what you execute (map or unmap), you have to surround it with
> > a LOCK/UNLOCK to provide support for atomic updates (GPU is blocked if
> > anything accesses the locked range while an update is on-going).  
> 
> That makes more sense, so these GPU drivers just flush the entire TLB
> every time they change it - built into the UNLOCK operation?

I don't have implementation details, so I can't really tell what
happens internally. What's sure is that LOCK takes a range, so they
might be optimizing the TLB flush to only evict entries covered by this
range, dunno.