diff mbox series

[v4,10/21] mm/mmap: Support vma == NULL in init_vma_munmap()

Message ID 20240710192250.4114783-11-Liam.Howlett@oracle.com (mailing list archive)
State New
Headers show
Series Avoid MAP_FIXED gap exposure | expand

Commit Message

Liam R. Howlett July 10, 2024, 7:22 p.m. UTC 
From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>

Adding support for a NULL vma means the init_vma_munmap() can be
initialized for a less error-prone process when calling
vms_complete_munmap_vmas() later on.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
---
 mm/mmap.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

Comments

Lorenzo Stoakes July 11, 2024, 2:28 p.m. UTC | #1 
On Wed, Jul 10, 2024 at 03:22:39PM GMT, Liam R. Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
>
> Adding support for a NULL vma means the init_vma_munmap() can be
> initialized for a less error-prone process when calling
> vms_complete_munmap_vmas() later on.
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
> ---
>  mm/mmap.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index a1544a68558e..e2e6b3202c25 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -516,10 +516,12 @@ static inline void init_vma_munmap(struct vma_munmap_struct *vms,
>  		bool unlock)
>  {
>  	vms->vmi = vmi;
> -	vms->vma = vma;
> -	vms->mm = vma->vm_mm;
> -	vms->start = start;
> -	vms->end = end;
> +	if (vma) {
> +		vms->vma = vma;
> +		vms->mm = vma->vm_mm;
> +		vms->start = start;
> +		vms->end = end;
> +	}

Why not store start/end even if !vma? And shouldn't we have an else clause
to make sure these are initialised in this case too?

I mean also we could have vms->vma = vma outside of this clause to so it
looks something like:

	vms->vma = vma;
	vms->mm = vma ? vma->vm_mm : NULL;
	vms->start = start;
	vms->end = end;

>  	vms->unlock = unlock;
>  	vms->uf = uf;
>  	vms->vma_count = 0;
> @@ -2950,11 +2952,11 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>
>  	/* Find the first overlapping VMA */
>  	vma = vma_find(&vmi, end);
> +	init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
>  	if (vma) {
>  		mt_init_flags(&mt_detach, vmi.mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
>  		mt_on_stack(mt_detach);
>  		mas_init(&mas_detach, &mt_detach, /* addr = */ 0);
> -		init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
>  		/* Prepare to unmap any existing mapping in the area */
>  		if (vms_gather_munmap_vmas(&vms, &mas_detach))
>  			return -ENOMEM;
> --
> 2.43.0
>

I really like this approach in general though!
Liam R. Howlett July 11, 2024, 4:04 p.m. UTC | #2 
* Lorenzo Stoakes <lorenzo.stoakes@oracle.com> [240711 10:28]:
> On Wed, Jul 10, 2024 at 03:22:39PM GMT, Liam R. Howlett wrote:
> > From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
> >
> > Adding support for a NULL vma means the init_vma_munmap() can be
> > initialized for a less error-prone process when calling
> > vms_complete_munmap_vmas() later on.
> >
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
> > ---
> >  mm/mmap.c | 12 +++++++-----
> >  1 file changed, 7 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index a1544a68558e..e2e6b3202c25 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -516,10 +516,12 @@ static inline void init_vma_munmap(struct vma_munmap_struct *vms,
> >  		bool unlock)
> >  {
> >  	vms->vmi = vmi;
> > -	vms->vma = vma;
> > -	vms->mm = vma->vm_mm;
> > -	vms->start = start;
> > -	vms->end = end;
> > +	if (vma) {
> > +		vms->vma = vma;
> > +		vms->mm = vma->vm_mm;
> > +		vms->start = start;
> > +		vms->end = end;
> > +	}
> 
> Why not store start/end even if !vma? And shouldn't we have an else clause
> to make sure these are initialised in this case too?
> 
> I mean also we could have vms->vma = vma outside of this clause to so it
> looks something like:
> 
> 	vms->vma = vma;
> 	vms->mm = vma ? vma->vm_mm : NULL;
> 	vms->start = start;
> 	vms->end = end;

I'd rather not set it the start/end as it implies there is a start/end
of an unmap operation that won't happen.  I'll just make it an else and
set them to 0.

> 
> >  	vms->unlock = unlock;
> >  	vms->uf = uf;
> >  	vms->vma_count = 0;
> > @@ -2950,11 +2952,11 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> >
> >  	/* Find the first overlapping VMA */
> >  	vma = vma_find(&vmi, end);
> > +	init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
> >  	if (vma) {
> >  		mt_init_flags(&mt_detach, vmi.mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
> >  		mt_on_stack(mt_detach);
> >  		mas_init(&mas_detach, &mt_detach, /* addr = */ 0);
> > -		init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
> >  		/* Prepare to unmap any existing mapping in the area */
> >  		if (vms_gather_munmap_vmas(&vms, &mas_detach))
> >  			return -ENOMEM;
> > --
> > 2.43.0
> >
> 
> I really like this approach in general though!
diff mbox series

Patch

diff --git a/mm/mmap.c b/mm/mmap.c
index a1544a68558e..e2e6b3202c25 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -516,10 +516,12 @@  static inline void init_vma_munmap(struct vma_munmap_struct *vms,
 		bool unlock)
 {
 	vms->vmi = vmi;
-	vms->vma = vma;
-	vms->mm = vma->vm_mm;
-	vms->start = start;
-	vms->end = end;
+	if (vma) {
+		vms->vma = vma;
+		vms->mm = vma->vm_mm;
+		vms->start = start;
+		vms->end = end;
+	}
 	vms->unlock = unlock;
 	vms->uf = uf;
 	vms->vma_count = 0;
@@ -2950,11 +2952,11 @@  unsigned long mmap_region(struct file *file, unsigned long addr,
 
 	/* Find the first overlapping VMA */
 	vma = vma_find(&vmi, end);
+	init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
 	if (vma) {
 		mt_init_flags(&mt_detach, vmi.mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
 		mt_on_stack(mt_detach);
 		mas_init(&mas_detach, &mt_detach, /* addr = */ 0);
-		init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
 		/* Prepare to unmap any existing mapping in the area */
 		if (vms_gather_munmap_vmas(&vms, &mas_detach))
 			return -ENOMEM;