Re: [PATCH 12/13] mm/mprotect: convert mprotect code to use vma_flags_t

[Lorenzo Stoakes <ljs@kernel.org>]

On Wed, Jul 08, 2026 at 10:16:15PM -0400, Zi Yan wrote:
> On Thu Jul 2, 2026 at 11:53 AM EDT, Lorenzo Stoakes wrote:
> > On Thu, Jul 02, 2026 at 12:09:17AM +0800, Lance Yang wrote:
> >>
> >> On Mon, Jun 29, 2026 at 08:25:35PM +0100, Lorenzo Stoakes wrote:
> >> >Replace use of the legacy vm_flags_t flags with vma_flags_t values
> >> >throughout the mprotect logic.
> >> >
> >> >Note that we retain the legacy vm_flags_t bit shifting code in
> >> >do_mprotect_key(), deferring a vma_flags_t approach to this for the time
> >> >being.
> >> >
> >> >Additionally update comments to reflect the changes to be consistent.
> >> >
> >> >No functional change intended.
> >> >
> >> >Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
> >> >---
> >> > mm/mprotect.c | 16 ++++++++--------
> >> > 1 file changed, 8 insertions(+), 8 deletions(-)
> >> >
> >> >diff --git a/mm/mprotect.c b/mm/mprotect.c
> >> >index 9cbf932b028c..c9504b2a2525 100644
> >> >--- a/mm/mprotect.c
> >> >+++ b/mm/mprotect.c
> >> >@@ -40,7 +40,7 @@
> >> >
> >> > static bool maybe_change_pte_writable(struct vm_area_struct *vma, pte_t pte)
> >> > {
> >> >-	if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE)))
> >> >+	if (WARN_ON_ONCE(!vma_test(vma, VMA_WRITE_BIT)))
> >> > 		return false;
> >> >
> >> > 	/* Don't touch entries that are not even readable. */
> >> >@@ -97,7 +97,7 @@ static bool can_change_shared_pte_writable(struct vm_area_struct *vma,
> >> > bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr,
> >> > 			     pte_t pte)
> >> > {
> >> >-	if (!(vma->vm_flags & VM_SHARED))
> >> >+	if (!vma_test(vma, VMA_SHARED_BIT))
> >> > 		return can_change_private_pte_writable(vma, addr, pte);
> >> >
> >> > 	return can_change_shared_pte_writable(vma, pte);
> >> >@@ -194,7 +194,7 @@ static __always_inline void set_write_prot_commit_flush_ptes(struct vm_area_stru
> >> > {
> >> > 	bool set_write;
> >> >
> >> >-	if (vma->vm_flags & VM_SHARED) {
> >> >+	if (vma_test(vma, VMA_SHARED_BIT)) {
> >> > 		set_write = can_change_shared_pte_writable(vma, ptent);
> >> > 		prot_commit_flush_ptes(vma, addr, ptep, oldpte, ptent, nr_ptes,
> >> > 				       /* idx = */ 0, set_write, tlb);
> >> >@@ -811,8 +811,8 @@ mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb,
> >> > 		vm_unacct_memory(nrpages);
> >> >
> >> > 	/*
> >> >-	 * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major
> >> >-	 * fault on access.
> >> >+	 * Private VMA_LOCKED_BIT VMA becoming writable: trigger COW to avoid
> >> >+	 * major fault on access.
> >> > 	 */
> >> > 	if (vma_flags_test(&new_vma_flags, VMA_WRITE_BIT) &&
> >> > 	    vma_flags_test(&old_vma_flags, VMA_LOCKED_BIT) &&
> >> >@@ -886,7 +886,7 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
> >> > 			goto out;
> >> > 		start = vma->vm_start;
> >> > 		error = -EINVAL;
> >> >-		if (!(vma->vm_flags & VM_GROWSDOWN))
> >> >+		if (!vma_test(vma, VMA_GROWSDOWN_BIT))
> >> > 			goto out;
> >> > 	} else {
> >> > 		if (vma->vm_start > start)
> >> >@@ -894,7 +894,7 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
> >> > 		if (unlikely(grows & PROT_GROWSUP)) {
> >> > 			end = vma->vm_end;
> >> > 			error = -EINVAL;
> >> >-			if (!(vma->vm_flags & VM_GROWSUP))
> >> >+			if (!vma_test(vma, VMA_GROWSUP_BIT))
> >>
> >> IIUC, should this be
> >>
> >> if (!vma_test_single_mask(vma, VMA_GROWSUP))
> >>
> >> instead?
> >>
> >> #elif defined(CONFIG_PARISC)
> >> #define VM_GROWSUP	INIT_VM_FLAG(GROWSUP)
> >> ...
> >> #ifndef VM_GROWSUP
> >> #define VM_GROWSUP	VM_NONE
> >> ...
> >>
> >> VM_GROWSUP is only defined as GROWSUP on parisc and becomes VM_NONE
> >> elsewhere. But VMA_GROWSUP_BIT is the raw ARCH_1 bit, which is also used
> >> for other arch-specific VMA flags:
> >>
> >> 	DECLARE_VMA_BIT_ALIAS(SAO, ARCH_1),		/* Strong Access Ordering (powerpc) */
> >> 	DECLARE_VMA_BIT_ALIAS(GROWSUP, ARCH_1),		/* parisc */
> >> 	DECLARE_VMA_BIT_ALIAS(SPARC_ADI, ARCH_1),	/* sparc64 */
> >> 	DECLARE_VMA_BIT_ALIAS(ARM64_BTI, ARCH_1),	/* arm64 */
> >> 	DECLARE_VMA_BIT_ALIAS(ARCH_CLEAR, ARCH_1),	/* sparc64, arm64 */
> >> 	DECLARE_VMA_BIT_ALIAS(MAPPED_COPY, ARCH_1),	/* !CONFIG_MMU */
> >>
> >> Other vma_test() changes look fine to me: just fixed INIT_VM_FLAG()
> >> masks matching their VMA_*_BIT :)
> >
> > Thanks you're right, will fix!
> >
> > Again I swear I ran claude on all of this so it's failing me here :)
> >
>
> Is it better to add something like below to avoid misuse these mutually
> exclusive bit aliases?
>
> An example for VMA_GROWSUP_BIT:
>
> #if defined(CONFIG_PARISC)
> DECLARE_VMA_BIT_ALIAS(GROWSUP, ARCH_1),		/* parisc */
> #else
> /* make VMA_GROWSUP_BIT a build bug on */
> #endif

Nah we can't...

>
> Hmm, these VMA_*_BIT are enum items, so the above might not be possible.

...because of this but also this is the canonical definition and we want to use
it for the VMA_xxx form.

> An alternative is to only define them for the corresponding config and
> you will get build errors when trying to use them directly and the
> config is not enabled. Otherwise, misuses like "vma_test(vma,
> VMA_GROWSUP_BIT)" is harder to uncover.

Yeah good idea, I may add a new DECLARE_INTERNAL_VMA_BIT() that gives you
__VMA_xxx_BIT, so nobody makes the obvious mistake and we force uses of safe
VMA_xxx form. Hmm :)

>
>
> --
> Best Regards,
> Yan, Zi
>

Thanks, Lorenzo