[v2,1/3] migrate.c: Remove vma check in migrate_vma_setup()

Commit Message

Alistair Popple Feb. 7, 2022, 4:26 a.m. UTC

migrate_vma_setup() checks that a valid vma is passed so that the page
tables can be walked to find the pfns associated with a given address
range. However in some cases the pfns are already known, such as when
migrating device coherent pages during pin_user_pages() meaning a valid
vma isn't required.

Signed-off-by: Alistair Popple <[e-mail]>
Acked-by: Felix Kuehling <[e-mail]>
---

Changes for v2:

 - Added Felix's Acked-by

 mm/migrate.c | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

Comments

John Hubbard Feb. 15, 2022, 9:50 p.m. UTC | #1

On 2/6/22 20:26, Alistair Popple wrote:
> migrate_vma_setup() checks that a valid vma is passed so that the page
> tables can be walked to find the pfns associated with a given address
> range. However in some cases the pfns are already known, such as when
> migrating device coherent pages during pin_user_pages() meaning a valid
> vma isn't required.
> 
> Signed-off-by: Alistair Popple <[e-mail]>
> Acked-by: Felix Kuehling <[e-mail]>
> ---
> 
> Changes for v2:
> 
>   - Added Felix's Acked-by
> 
>   mm/migrate.c | 34 +++++++++++++++++-----------------
>   1 file changed, 17 insertions(+), 17 deletions(-)
> 

Hi Alistair,

Another late-breaking review question, below. :)

> diff --git a/mm/migrate.c b/mm/migrate.c
> index a9aed12..0d6570d 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2602,24 +2602,24 @@ int migrate_vma_setup(struct migrate_vma *args)
>   
>   	args->start &= PAGE_MASK;
>   	args->end &= PAGE_MASK;
> -	if (!args->vma || is_vm_hugetlb_page(args->vma) ||
> -	    (args->vma->vm_flags & VM_SPECIAL) || vma_is_dax(args->vma))
> -		return -EINVAL;
> -	if (nr_pages <= 0)
> -		return -EINVAL;

Was the above check left out intentionally? If so, then it needs a
commit description note. And maybe even a separate patch, because it
changes the behavior.

If you do want to change the behavior:

* The kerneldoc comment above this function supports such a change: it
requires returning 0 for the case of zero pages requested. So your
change would bring the comments into alignment with the code.

* I don't think memset deals properly with a zero length input arg, so
it's probably better to return 0, before that point.


thanks,

Patch

diff --git a/mm/migrate.c b/mm/migrate.c
index a9aed12..0d6570d 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2602,24 +2602,24 @@  int migrate_vma_setup(struct migrate_vma *args)
 
 	args->start &= PAGE_MASK;
 	args->end &= PAGE_MASK;
-	if (!args->vma || is_vm_hugetlb_page(args->vma) ||
-	    (args->vma->vm_flags & VM_SPECIAL) || vma_is_dax(args->vma))
-		return -EINVAL;
-	if (nr_pages <= 0)
-		return -EINVAL;
-	if (args->start < args->vma->vm_start ||
-	    args->start >= args->vma->vm_end)
-		return -EINVAL;
-	if (args->end <= args->vma->vm_start || args->end > args->vma->vm_end)
-		return -EINVAL;
 	if (!args->src || !args->dst)
 		return -EINVAL;
-
-	memset(args->src, 0, sizeof(*args->src) * nr_pages);
-	args->cpages = 0;
-	args->npages = 0;
-
-	migrate_vma_collect(args);
+	if (args->vma) {
+		if (is_vm_hugetlb_page(args->vma) ||
+			(args->vma->vm_flags & VM_SPECIAL) || vma_is_dax(args->vma))
+			return -EINVAL;
+		if (args->start < args->vma->vm_start ||
+			args->start >= args->vma->vm_end)
+			return -EINVAL;
+		if (args->end <= args->vma->vm_start || args->end > args->vma->vm_end)
+			return -EINVAL;
+
+		memset(args->src, 0, sizeof(*args->src) * nr_pages);
+		args->cpages = 0;
+		args->npages = 0;
+
+		migrate_vma_collect(args);
+	}
 
 	if (args->cpages)
 		migrate_vma_unmap(args);
@@ -2804,7 +2804,7 @@  void migrate_vma_pages(struct migrate_vma *migrate)
 			continue;
 		}
 
-		if (!page) {
+		if (!page && migrate->vma) {
 			if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE))
 				continue;
 			if (!notified) {