linux-kernel - Re: [PATCH v3] io: add io

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Message-ID: <aRtOfhNjlCavCTjU@google.com>
Date: Mon, 17 Nov 2025 16:34:06 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Will Deacon <will@...nel.org>, 
	Boris Brezillon <boris.brezillon@...labora.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>, Robin Murphy <robin.murphy@....com>, 
	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 v3] io: add io_pgtable abstraction

On Wed, Nov 12, 2025 at 09:57:09AM -0300, Daniel Almeida wrote:
> Hi Alice,
> 
> > On 12 Nov 2025, at 07:15, Alice Ryhl <aliceryhl@...gle.com> wrote:
> > +    /// Map a physically contiguous range of pages of the same size.
> > +    ///
> > +    /// # Safety
> > +    ///
> > +    /// * This page table must not contain any mapping that overlaps with the mapping created by
> > +    ///   this call.
> 
> I don't think there is a restriction that forbids you from mapping a region that has already been mapped.
> 
> If A->B->C are adjacent regions, and you try to map A -> C when B->C is already mapped, I think this
> call will simply return length(A->B).

I think that such overlapping ranges are not allowed. It triggers a
warn:

        } else if (pte) {                                                           
                /* We require an unmap first */                                 
                WARN_ON(!(cfg->quirks & IO_PGTABLE_QUIRK_NO_WARN));             
                return -EEXIST;

Alice