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Message-ID: <37092fb8-c8f7-4d9e-ba43-f2104e33f388@nvidia.com>
Date: Tue, 7 Oct 2025 19:36:42 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Alice Ryhl <aliceryhl@...gle.com>, acsjakub@...zon.de
Cc: akpm@...ux-foundation.org, axelrasmussen@...gle.com,
chengming.zhou@...ux.dev, david@...hat.com, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org, peterx@...hat.com,
xu.xin16@....com.cn, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH] mm: use enum for vm_flags
On 10/7/25 9:21 AM, Alice Ryhl wrote:
> The bindgen tool is better able to handle BIT(_) declarations when used
> in an enum.
>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
> Hi Jakub,
>
> what do you think about modifying the patch like this to use an enum? It
> resolves the issues brought up in
> https://lore.kernel.org/all/CAH5fLghTu-Zcm9e3Hy07nNtvB_-hRjojAWDoq-hhBYGE7LPEbQ@mail.gmail.com/
>
> Feel free to squash this patch into your patch.
>
> include/linux/mm.h | 90 +++++++++++++++++----------------
> rust/bindings/bindings_helper.h | 1 -
> 2 files changed, 46 insertions(+), 45 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 7916d527f687..69da7ce13e50 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -273,57 +273,58 @@ extern unsigned int kobjsize(const void *objp);
> * vm_flags in vm_area_struct, see mm_types.h.
> * When changing, update also include/trace/events/mmflags.h
> */
> -#define VM_NONE 0
> +enum {
> + VM_NONE = 0,
>
> -#define VM_READ BIT(0) /* currently active flags */
> -#define VM_WRITE BIT(1)
> -#define VM_EXEC BIT(2)
> -#define VM_SHARED BIT(3)
> + VM_READ = BIT(0), /* currently active flags */
> + VM_WRITE = BIT(1),
> + VM_EXEC = BIT(2),
> + VM_SHARED = BIT(3),
Hi Alice,
If this approach actually works, then I think it is a reasonable
trade off, given that Rust's bindgen(1) is not going to be able
to help us for a while.
In other words, a small change to mm.h's format here, to avoid
a messy sort of "forked" copy of these over in
rust/bindings/bindings_helper.h, seems better overall.
At least, I think it's better. :)
thanks,
John Hubbard
>
> /* mprotect() hardcodes VM_MAYREAD >> 4 == VM_READ, and so for r/w/x bits. */
> -#define VM_MAYREAD BIT(4) /* limits for mprotect() etc */
> -#define VM_MAYWRITE BIT(5)
> -#define VM_MAYEXEC BIT(6)
> -#define VM_MAYSHARE BIT(7)
> + VM_MAYREAD = BIT(4), /* limits for mprotect() etc */
> + VM_MAYWRITE = BIT(5),
> + VM_MAYEXEC = BIT(6),
> + VM_MAYSHARE = BIT(7),
>
> -#define VM_GROWSDOWN BIT(8) /* general info on the segment */
> + VM_GROWSDOWN = BIT(8), /* general info on the segment */
> #ifdef CONFIG_MMU
> -#define VM_UFFD_MISSING BIT(9) /* missing pages tracking */
> + VM_UFFD_MISSING = BIT(9), /* missing pages tracking */
> #else /* CONFIG_MMU */
> -#define VM_MAYOVERLAY BIT(9) /* nommu: R/O MAP_PRIVATE mapping that might overlay a file mapping */
> + VM_MAYOVERLAY = BIT(9), /* nommu: R/O MAP_PRIVATE mapping that might overlay a file mapping */
> #define VM_UFFD_MISSING 0
> #endif /* CONFIG_MMU */
> -#define VM_PFNMAP BIT(10) /* Page-ranges managed without "struct page", just pure PFN */
> -#define VM_UFFD_WP BIT(12) /* wrprotect pages tracking */
> -
> -#define VM_LOCKED BIT(13)
> -#define VM_IO BIT(14) /* Memory mapped I/O or similar */
> -
> - /* Used by sys_madvise() */
> -#define VM_SEQ_READ BIT(15) /* App will access data sequentially */
> -#define VM_RAND_READ BIT(16) /* App will not benefit from clustered reads */
> -
> -#define VM_DONTCOPY BIT(17) /* Do not copy this vma on fork */
> -#define VM_DONTEXPAND BIT(18) /* Cannot expand with mremap() */
> -#define VM_LOCKONFAULT BIT(19) /* Lock the pages covered when they are faulted in */
> -#define VM_ACCOUNT BIT(20) /* Is a VM accounted object */
> -#define VM_NORESERVE BIT(21) /* should the VM suppress accounting */
> -#define VM_HUGETLB BIT(22) /* Huge TLB Page VM */
> -#define VM_SYNC BIT(23) /* Synchronous page faults */
> -#define VM_ARCH_1 BIT(24) /* Architecture-specific flag */
> -#define VM_WIPEONFORK BIT(25) /* Wipe VMA contents in child. */
> -#define VM_DONTDUMP BIT(26) /* Do not include in the core dump */
> + VM_PFNMAP = BIT(10), /* Page-ranges managed without "struct page", just pure PFN */
> + VM_UFFD_WP = BIT(12), /* wrprotect pages tracking */
> +
> + VM_LOCKED = BIT(13),
> + VM_IO = BIT(14), /* Memory mapped I/O or similar */
> +
> + /* Used by sys_madvise() */
> + VM_SEQ_READ = BIT(15), /* App will access data sequentially */
> + VM_RAND_READ = BIT(16), /* App will not benefit from clustered reads */
> +
> + VM_DONTCOPY = BIT(17), /* Do not copy this vma on fork */
> + VM_DONTEXPAND = BIT(18), /* Cannot expand with mremap() */
> + VM_LOCKONFAULT = BIT(19), /* Lock the pages covered when they are faulted in */
> + VM_ACCOUNT = BIT(20), /* Is a VM accounted object */
> + VM_NORESERVE = BIT(21), /* should the VM suppress accounting */
> + VM_HUGETLB = BIT(22), /* Huge TLB Page VM */
> + VM_SYNC = BIT(23), /* Synchronous page faults */
> + VM_ARCH_1 = BIT(24), /* Architecture-specific flag */
> + VM_WIPEONFORK = BIT(25), /* Wipe VMA contents in child. */
> + VM_DONTDUMP = BIT(26), /* Do not include in the core dump */
>
> #ifdef CONFIG_MEM_SOFT_DIRTY
> -# define VM_SOFTDIRTY BIT(27) /* Not soft dirty clean area */
> + VM_SOFTDIRTY = BIT(27), /* Not soft dirty clean area */
> #else
> # define VM_SOFTDIRTY 0
> #endif
>
> -#define VM_MIXEDMAP BIT(28) /* Can contain "struct page" and pure PFN pages */
> -#define VM_HUGEPAGE BIT(29) /* MADV_HUGEPAGE marked this vma */
> -#define VM_NOHUGEPAGE BIT(30) /* MADV_NOHUGEPAGE marked this vma */
> -#define VM_MERGEABLE BIT(31) /* KSM may merge identical pages */
> + VM_MIXEDMAP = BIT(28), /* Can contain "struct page" and pure PFN pages */
> + VM_HUGEPAGE = BIT(29), /* MADV_HUGEPAGE marked this vma */
> + VM_NOHUGEPAGE = BIT(30), /* MADV_NOHUGEPAGE marked this vma */
> + VM_MERGEABLE = BIT(31), /* KSM may merge identical pages */
>
> #ifdef CONFIG_ARCH_USES_HIGH_VMA_FLAGS
> #define VM_HIGH_ARCH_BIT_0 32 /* bit only usable on 64-bit architectures */
> @@ -333,14 +334,15 @@ extern unsigned int kobjsize(const void *objp);
> #define VM_HIGH_ARCH_BIT_4 36 /* bit only usable on 64-bit architectures */
> #define VM_HIGH_ARCH_BIT_5 37 /* bit only usable on 64-bit architectures */
> #define VM_HIGH_ARCH_BIT_6 38 /* bit only usable on 64-bit architectures */
> -#define VM_HIGH_ARCH_0 BIT(VM_HIGH_ARCH_BIT_0)
> -#define VM_HIGH_ARCH_1 BIT(VM_HIGH_ARCH_BIT_1)
> -#define VM_HIGH_ARCH_2 BIT(VM_HIGH_ARCH_BIT_2)
> -#define VM_HIGH_ARCH_3 BIT(VM_HIGH_ARCH_BIT_3)
> -#define VM_HIGH_ARCH_4 BIT(VM_HIGH_ARCH_BIT_4)
> -#define VM_HIGH_ARCH_5 BIT(VM_HIGH_ARCH_BIT_5)
> -#define VM_HIGH_ARCH_6 BIT(VM_HIGH_ARCH_BIT_6)
> + VM_HIGH_ARCH_0 = BIT(VM_HIGH_ARCH_BIT_0),
> + VM_HIGH_ARCH_1 = BIT(VM_HIGH_ARCH_BIT_1),
> + VM_HIGH_ARCH_2 = BIT(VM_HIGH_ARCH_BIT_2),
> + VM_HIGH_ARCH_3 = BIT(VM_HIGH_ARCH_BIT_3),
> + VM_HIGH_ARCH_4 = BIT(VM_HIGH_ARCH_BIT_4),
> + VM_HIGH_ARCH_5 = BIT(VM_HIGH_ARCH_BIT_5),
> + VM_HIGH_ARCH_6 = BIT(VM_HIGH_ARCH_BIT_6),
> #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */
> +};
>
> #ifdef CONFIG_ARCH_HAS_PKEYS
> # define VM_PKEY_SHIFT VM_HIGH_ARCH_BIT_0
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index 2e43c66635a2..04b75d4d01c3 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -108,7 +108,6 @@ 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;
>
> #if IS_ENABLED(CONFIG_ANDROID_BINDER_IPC_RUST)
> #include "../../drivers/android/binder/rust_binder.h"
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