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SubjectRe: [PATCH 01/16] mm: use untagged_addr() for get_user_pages_fast addresses
On Tue, Jun 11, 2019 at 04:40:47PM +0200, Christoph Hellwig wrote:
> This will allow sparc64 to override its ADI tags for
> get_user_pages and get_user_pages_fast.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> mm/gup.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index ddde097cf9e4..6bb521db67ec 100644
> +++ b/mm/gup.c
> @@ -2146,7 +2146,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
> unsigned long flags;
> int nr = 0;
>
> - start &= PAGE_MASK;
> + start = untagged_addr(start) & PAGE_MASK;
> len = (unsigned long) nr_pages << PAGE_SHIFT;
> end = start + len;

Hmm, this function, and the other, goes on to do:

if (unlikely(!access_ok((void __user *)start, len)))
return 0;

and I thought that access_ok takes in the tagged pointer?

How about re-order it a bit?

diff --git a/mm/gup.c b/mm/gup.c
index ddde097cf9e410..f48747ced4723b 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2148,11 +2148,12 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,

start &= PAGE_MASK;
len = (unsigned long) nr_pages << PAGE_SHIFT;
- end = start + len;
-
if (unlikely(!access_ok((void __user *)start, len)))
return 0;

+ start = untagged_ptr(start);
+ end = start + len;
+
/*
* Disable interrupts. We use the nested form as we can already have
* interrupts disabled by get_futex_key.
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