linux-kernel - Re: [PATCH v2 1/4] mm: declare VMA flags by bit

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Message-ID: <7d63aa31-e77e-4b60-9edb-aeef17849388@lucifer.local>
Date: Fri, 14 Nov 2025 14:11:31 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Muchun Song <muchun.song@...ux.dev>,
        Oscar Salvador <osalvador@...e.de>,
        David Hildenbrand <david@...hat.com>,
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        rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v2 1/4] mm: declare VMA flags by bit

On Fri, Nov 14, 2025 at 03:08:21PM +0100, Alice Ryhl wrote:
> On Fri, Nov 14, 2025 at 3:02 PM Lorenzo Stoakes
> <lorenzo.stoakes@...cle.com> wrote:
> >
> > On Fri, Nov 14, 2025 at 01:50:45PM +0000, Alice Ryhl wrote:
> > > On Fri, Nov 14, 2025 at 01:26:08PM +0000, Lorenzo Stoakes wrote:
> > > > diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> > > > index 2e43c66635a2..4c327db01ca0 100644
> > > > --- a/rust/bindings/bindings_helper.h
> > > > +++ b/rust/bindings/bindings_helper.h
> > > > @@ -108,7 +108,32 @@ const xa_mark_t RUST_CONST_HELPER_XA_PRESENT = XA_PRESENT;
> > > >
> > > >  const gfp_t RUST_CONST_HELPER_XA_FLAGS_ALLOC = XA_FLAGS_ALLOC;
> > > >  const gfp_t RUST_CONST_HELPER_XA_FLAGS_ALLOC1 = XA_FLAGS_ALLOC1;
> > > > +
> > > >  const vm_flags_t RUST_CONST_HELPER_VM_MERGEABLE = VM_MERGEABLE;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_READ = VM_READ;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_WRITE = VM_WRITE;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_EXEC = VM_EXEC;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_SHARED = VM_SHARED;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_MAYREAD = VM_MAYREAD;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_MAYWRITE = VM_MAYWRITE;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_MAYEXEC = VM_MAYEXEC;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_MAYSHARE = VM_MAYEXEC;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_PFNMAP = VM_PFNMAP;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_IO = VM_IO;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_DONTCOPY = VM_DONTCOPY;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_DONTEXPAND = VM_DONTEXPAND;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_LOCKONFAULT = VM_LOCKONFAULT;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_ACCOUNT = VM_ACCOUNT;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_NORESERVE = VM_NORESERVE;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_HUGETLB = VM_HUGETLB;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_SYNC = VM_SYNC;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_ARCH_1 = VM_ARCH_1;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_WIPEONFORK = VM_WIPEONFORK;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_DONTDUMP = VM_DONTDUMP;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_SOFTDIRTY = VM_SOFTDIRTY;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_MIXEDMAP = VM_MIXEDMAP;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_HUGEPAGE = VM_HUGEPAGE;
> > > > +const vm_flags_t RUST_CONST_HELPER_VM_NOHUGEPAGE = VM_NOHUGEPAGE;
> > >
> > > I got this error:
> > >
> > > error[E0428]: the name `VM_SOFTDIRTY` is defined multiple times
> > >       --> rust/bindings/bindings_generated.rs:115967:1
> > >        |
> > > 13440  | pub const VM_SOFTDIRTY: u32 = 0;
> > >        | -------------------------------- previous definition of the value `VM_SOFTDIRTY` here
> > > ...
> > > 115967 | pub const VM_SOFTDIRTY: vm_flags_t = 0;
> > >        | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `VM_SOFTDIRTY` redefined here
> > >        |
> > >        = note: `VM_SOFTDIRTY` must be defined only once in the value namespace of this module
> > >
> >
> > That's odd, obviously I build tested this and didn't get the same error.
> >
> > Be good to know what config options to enable for testing for rust. I repro'd
> > the previously reported issues, and new ones since I'm now declaring these
> > values consistently using BIT().
> >
> > But in my build locally, no errors with LLVM=1 and CONFIG_RUST=y.
>
> I got this error because my config defines VM_SOFTDIRTY as VM_NONE,
> which bindgen can resolve to zero. You probably have a config where
> it's defined using a function-like macro, so bindgen did not generate
> a duplicate for you.

Ugh yeah of course, damn.

>
> > > Please add the constants in rust/bindgen_parameters next to
> > > ARCH_KMALLOC_MINALIGN to avoid this error. This ensures that only the
> > > version from bindings_helper.h is generated.
> >
> > As in
> >
> > --block-list-item <VM_blah> for every flag?
>
> Yes.

OK will send a fixpatch, better to add them all to be safe.

Bit ugly but we can fix this up later when I add in the actual accessor
helpers.

>
> Alice
>

Thanks, Lorenzo