diff mbox series

[v2,17/19] powerpc: book3s64: convert to pin_user_pages() and put_user_page()

Message ID 20191125231035.1539120-18-jhubbard@nvidia.com (mailing list archive)
State New
Headers show
Series pin_user_pages(): reduced-risk series for Linux 5.5 | expand

Commit Message

John Hubbard Nov. 25, 2019, 11:10 p.m. UTC
1. Convert from get_user_pages() to pin_user_pages().

2. As required by pin_user_pages(), release these pages via
put_user_page(). In this case, do so via put_user_pages_dirty_lock().

That has the side effect of calling set_page_dirty_lock(), instead
of set_page_dirty(). This is probably more accurate.

As Christoph Hellwig put it, "set_page_dirty() is only safe if we are
dealing with a file backed page where we have reference on the inode it
hangs off." [1]

[1] https://lore.kernel.org/r/20190723153640.GB720@lst.de

Cc: Jan Kara <jack@suse.cz>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 arch/powerpc/mm/book3s64/iommu_api.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

Comments

Jan Kara Nov. 29, 2019, 11:23 a.m. UTC | #1
On Mon 25-11-19 15:10:33, John Hubbard wrote:
> 1. Convert from get_user_pages() to pin_user_pages().
> 
> 2. As required by pin_user_pages(), release these pages via
> put_user_page(). In this case, do so via put_user_pages_dirty_lock().
> 
> That has the side effect of calling set_page_dirty_lock(), instead
> of set_page_dirty(). This is probably more accurate.

Maybe more accurate but it doesn't work for mm_iommu_unpin(). As I'm
checking mm_iommu_unpin() gets called from RCU callback which is executed
interrupt context and you cannot lock pages from such context. So you need
to queue work from the RCU callback and then do the real work from the
workqueue...

								Honza

> 
> As Christoph Hellwig put it, "set_page_dirty() is only safe if we are
> dealing with a file backed page where we have reference on the inode it
> hangs off." [1]
> 
> [1] https://lore.kernel.org/r/20190723153640.GB720@lst.de
> 
> Cc: Jan Kara <jack@suse.cz>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  arch/powerpc/mm/book3s64/iommu_api.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/powerpc/mm/book3s64/iommu_api.c b/arch/powerpc/mm/book3s64/iommu_api.c
> index 56cc84520577..fc1670a6fc3c 100644
> --- a/arch/powerpc/mm/book3s64/iommu_api.c
> +++ b/arch/powerpc/mm/book3s64/iommu_api.c
> @@ -103,7 +103,7 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
>  	for (entry = 0; entry < entries; entry += chunk) {
>  		unsigned long n = min(entries - entry, chunk);
>  
> -		ret = get_user_pages(ua + (entry << PAGE_SHIFT), n,
> +		ret = pin_user_pages(ua + (entry << PAGE_SHIFT), n,
>  				FOLL_WRITE | FOLL_LONGTERM,
>  				mem->hpages + entry, NULL);
>  		if (ret == n) {
> @@ -167,9 +167,8 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
>  	return 0;
>  
>  free_exit:
> -	/* free the reference taken */
> -	for (i = 0; i < pinned; i++)
> -		put_page(mem->hpages[i]);
> +	/* free the references taken */
> +	put_user_pages(mem->hpages, pinned);
>  
>  	vfree(mem->hpas);
>  	kfree(mem);
> @@ -212,10 +211,9 @@ static void mm_iommu_unpin(struct mm_iommu_table_group_mem_t *mem)
>  		if (!page)
>  			continue;
>  
> -		if (mem->hpas[i] & MM_IOMMU_TABLE_GROUP_PAGE_DIRTY)
> -			SetPageDirty(page);
> +		put_user_pages_dirty_lock(&page, 1,
> +				mem->hpas[i] & MM_IOMMU_TABLE_GROUP_PAGE_DIRTY);
>  
> -		put_page(page);
>  		mem->hpas[i] = 0;
>  	}
>  }
> -- 
> 2.24.0
>
John Hubbard Nov. 29, 2019, 9:44 p.m. UTC | #2
On 11/29/19 3:23 AM, Jan Kara wrote:
> On Mon 25-11-19 15:10:33, John Hubbard wrote:
>> 1. Convert from get_user_pages() to pin_user_pages().
>>
>> 2. As required by pin_user_pages(), release these pages via
>> put_user_page(). In this case, do so via put_user_pages_dirty_lock().
>>
>> That has the side effect of calling set_page_dirty_lock(), instead
>> of set_page_dirty(). This is probably more accurate.
> 
> Maybe more accurate but it doesn't work for mm_iommu_unpin(). As I'm
> checking mm_iommu_unpin() gets called from RCU callback which is executed
> interrupt context and you cannot lock pages from such context. So you need
> to queue work from the RCU callback and then do the real work from the
> workqueue...
> 
> 								Honza

ah yes, fixed locally. (In order to avoid  distracting people during the merge
window, I won't post any more versions of the series until the merge window is
over, unless a maintainer tells me that any of these patches are desired for
5.5.)

With that, we are back to a one-line diff for this part:

@@ -215,7 +214,7 @@ static void mm_iommu_unpin(struct mm_iommu_table_group_mem_t *mem)
                 if (mem->hpas[i] & MM_IOMMU_TABLE_GROUP_PAGE_DIRTY)
                         SetPageDirty(page);
  
-               put_page(page);
+               put_user_page(page);
                 mem->hpas[i] = 0;
         }
  }

btw, I'm also working on your feedback for patch 17 (mm/gup: track FOLL_PIN pages [1]),
from a few days earlier, it's not being ignored, I'm just trying to avoid distracting
people during the merge window.

[1] https://lore.kernel.org/r/20191121093941.GA18190@quack2.suse.cz

thanks,
diff mbox series

Patch

diff --git a/arch/powerpc/mm/book3s64/iommu_api.c b/arch/powerpc/mm/book3s64/iommu_api.c
index 56cc84520577..fc1670a6fc3c 100644
--- a/arch/powerpc/mm/book3s64/iommu_api.c
+++ b/arch/powerpc/mm/book3s64/iommu_api.c
@@ -103,7 +103,7 @@  static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
 	for (entry = 0; entry < entries; entry += chunk) {
 		unsigned long n = min(entries - entry, chunk);
 
-		ret = get_user_pages(ua + (entry << PAGE_SHIFT), n,
+		ret = pin_user_pages(ua + (entry << PAGE_SHIFT), n,
 				FOLL_WRITE | FOLL_LONGTERM,
 				mem->hpages + entry, NULL);
 		if (ret == n) {
@@ -167,9 +167,8 @@  static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
 	return 0;
 
 free_exit:
-	/* free the reference taken */
-	for (i = 0; i < pinned; i++)
-		put_page(mem->hpages[i]);
+	/* free the references taken */
+	put_user_pages(mem->hpages, pinned);
 
 	vfree(mem->hpas);
 	kfree(mem);
@@ -212,10 +211,9 @@  static void mm_iommu_unpin(struct mm_iommu_table_group_mem_t *mem)
 		if (!page)
 			continue;
 
-		if (mem->hpas[i] & MM_IOMMU_TABLE_GROUP_PAGE_DIRTY)
-			SetPageDirty(page);
+		put_user_pages_dirty_lock(&page, 1,
+				mem->hpas[i] & MM_IOMMU_TABLE_GROUP_PAGE_DIRTY);
 
-		put_page(page);
 		mem->hpas[i] = 0;
 	}
 }