Re: [PATCH 01/13] mm: introduce vma_flags_can_grow() and vma_can_grow()

[Lorenzo Stoakes <ljs@kernel.org>]

On Mon, Jun 29, 2026 at 04:26:18PM -0400, Zi Yan wrote:
> On Mon Jun 29, 2026 at 3:25 PM EDT, Lorenzo Stoakes wrote:
> > These test whether the VMA has stack sematics, i.e. is able to grow upwards
> > or downwards depending on the architecture.
> >
> > In order to account for arches which do not support upward-growing stacks,
> > introduce VMA_GROWSUP whose definition depends on the architecture
> > supporting it, and use vma_flags_test_single_mask() in vma_flags_can_grow()
> > to account for this.
> >
> > Update the VMA userland tests to reflect the changes
> >
> > No functional change intended.
> >
> > Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
> > ---
> >  include/linux/mm.h              | 21 ++++++++++++++++++---
> >  tools/testing/vma/include/dup.h |  4 ++++
> >  2 files changed, 22 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 868b2334bff3..cf7df1569052 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -472,6 +472,7 @@ enum {
> >  #define VM_SAO		INIT_VM_FLAG(SAO)
> >  #elif defined(CONFIG_PARISC)
> >  #define VM_GROWSUP	INIT_VM_FLAG(GROWSUP)
> > +#define VMA_GROWSUP	mk_vma_flags(VMA_GROWSUP_BIT)
> >  #elif defined(CONFIG_SPARC64)
> >  #define VM_SPARC_ADI	INIT_VM_FLAG(SPARC_ADI)
> >  #define VM_ARCH_CLEAR	INIT_VM_FLAG(ARCH_CLEAR)
> > @@ -483,6 +484,7 @@ enum {
> >  #endif
> >  #ifndef VM_GROWSUP
> >  #define VM_GROWSUP	VM_NONE
> > +#define VMA_GROWSUP	EMPTY_VMA_FLAGS
> >  #endif
> >  #ifdef CONFIG_ARM64_MTE
> >  #define VM_MTE		INIT_VM_FLAG(MTE)
> > @@ -1563,11 +1565,24 @@ static inline bool vma_is_initial_stack(const struct vm_area_struct *vma)
> >  		vma->vm_end >= vma->vm_mm->start_stack;
> >  }
> >
> > -static inline bool vma_is_temporary_stack(const struct vm_area_struct *vma)
> > +static inline bool vma_flags_can_grow(const vma_flags_t *flags)
> >  {
> > -	int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);
> > +	if (vma_flags_test_single_mask(flags, VMA_GROWSUP))
> > +		return true;
> > +	if (vma_flags_test(flags, VMA_GROWSDOWN_BIT))
> > +		return true;
> > +
> > +	return false;
> > +}
> >
> > -	if (!maybe_stack)
> > +static inline bool vma_can_grow(const struct vm_area_struct *vma)
> > +{
> > +	return vma_flags_can_grow(&vma->flags);
>
> Would it save vma_flags_can_grow() if we do below?
>
> return vma_test(vma, VMA_GROWSDOWN_BIT) || vma_test_single_mask(vma, VMA_GROWSUP);
>
> I find these two functions when I am reading mm.h.

Yeah but we require vma_flags_can_grow() for code in mmap.c, the majority of
checks of this have only vma_flags_t to work with not a VMA :)

>
> > +}
> > +
> > +static inline bool vma_is_temporary_stack(const struct vm_area_struct *vma)
> > +{
> > +	if (!vma_can_grow(vma))
> >  		return false;
> >
> >  	if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) ==
> > diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
> > index 5d7d0afd7765..6f5bcd7fbcd8 100644
> > --- a/tools/testing/vma/include/dup.h
> > +++ b/tools/testing/vma/include/dup.h
> > @@ -245,8 +245,10 @@ enum {
> >  #define VM_STACK	INIT_VM_FLAG(STACK)
> >  #ifdef CONFIG_STACK_GROWS_UP
> >  #define VM_STACK_EARLY	INIT_VM_FLAG(STACK_EARLY)
> > +#define VMA_STACK_EARLY mk_vma_flags(VMA_STACK_EARLY_BIT)
> >  #else
> >  #define VM_STACK_EARLY	VM_NONE
> > +#define VMA_STACK_EARLY EMPTY_VMA_FLAGS
> >  #endif
> >  #ifdef CONFIG_ARCH_HAS_PKEYS
> >  #define VM_PKEY_SHIFT ((__force int)VMA_HIGH_ARCH_0_BIT)
> > @@ -315,6 +317,8 @@ enum {
> >
> >  /* Bits set in the VMA until the stack is in its final location */
> >  #define VM_STACK_INCOMPLETE_SETUP (VM_RAND_READ | VM_SEQ_READ | VM_STACK_EARLY)
> > +#define VMA_STACK_INCOMPLETE_SETUP append_vma_flags(		\
> > +	VMA_STACK_EARLY, VMA_RAND_READ_BIT, VMA_SEQ_READ_BIT)
> >
> >  #define TASK_EXEC_BIT ((current->personality & READ_IMPLIES_EXEC) ? \
> >  		       VM_EXEC_BIT : VM_READ_BIT)
>
> Why are VMA_STACK_EARLY and VMA_STACK_INCOMPLETE_SETUP added here but
> not in mm.h?

Yeah urgh oops my bad. It doesn't really break anything but I'll fix it if a
respin is needed...

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

Thanks, Lorenzo