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

["Zi Yan" <ziy@xxxxxxxxxx>]

On Tue Jun 30, 2026 at 3:38 AM EDT, Lorenzo Stoakes wrote:
> 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@xxxxxxxxxx>
>> > ---
>> >  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 :)
>

Got it. I think I need to finish this series. :)

>>
>> > +}
>> > +
>> > +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...

Sure.

-- 
Best Regards,
Yan, Zi