Re: Linux 5.1-rc5

[Linus Torvalds]

On Tue, Apr 16, 2019 at 9:16 AM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> We actually already *have* this function.
>
> It's called "gup_fast_permitted()" and it's used by x86-64 to verify
> the proper address range. Exactly like s390 needs..
>
> Could you please use that instead?

IOW, something like the attached.

Obviously untested. And maybe 'current' isn't declared in
<asm/pgtable.h>, in which case you'd need to modify it to instead make
the inline function be "s390_gup_fast_permitted()" that takes a
pointer to the mm, and do something like

  #define gup_fast_permitted(start, pages) \
         s390_gup_fast_permitted(current->mm, start, pages)

instead.

But I think you get the idea..

                Linus
 arch/s390/include/asm/pgtable.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 76dc344edb8c..a08248995f50 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -1659,4 +1659,16 @@ static inline void check_pgt_cache(void) { }
 
 #include <asm-generic/pgtable.h>
 
+static inline bool gup_fast_permitted(unsigned long start, int nr_pages)
+{
+	unsigned long len, end;
+
+	len = (unsigned long)nr_pages << PAGE_SHIFT;
+	end = start + len;
+	if (end < start)
+		return false;
+	return end <= current->mm->context.asce_limit;
+}
+#define gup_fast_permitted gup_fast_permitted
+
 #endif /* _S390_PAGE_H */