s390/trng: Replace __get_free_page() with kmalloc()

trng_read() allocates a temporary staging buffer for CPACF TRNG
random data before copying it to userspace.

This buffer can be allocated with kmalloc() as there's nothing special
about it to go directly to the page allocator.

kmalloc() provides a better API that does not require ugly casts and
kfree() does not need to know the size of the freed object.

Performance difference between kmalloc() and __get_free_pages() is not
measurable as both allocators take an object/page from a per-CPU list for
fast path allocations.

For the slow path the performance is anyway determined by the amount of
reclaim involved rather than by what allocator is used.

Replace use of __get_free_page() with kmalloc() and free_page() with
kfree().

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

diff --git a/drivers/char/hw_random/s390-trng.c b/drivers/char/hw_random/s390-trng.c
index 3024d5e9fd61ff0edc7ac7510258908b85a396f3..5520f66274b3c6a7aa97051fa4c75c6049c391ee 100644 (file)
--- a/drivers/char/hw_random/s390-trng.c
+++ b/drivers/char/hw_random/s390-trng.c
@@ -20,6 +20,7 @@
 #include <linux/atomic.h>
 #include <linux/random.h>
 #include <linux/sched/signal.h>
+#include <linux/slab.h>
 #include <asm/debug.h>
 #include <asm/cpacf.h>
 #include <asm/archrandom.h>
@@ -67,7 +68,7 @@ static ssize_t trng_read(struct file *file, char __user *ubuf,
         */
 
        if (nbytes > sizeof(buf)) {
-               p = (u8 *) __get_free_page(GFP_KERNEL);
+               p = kmalloc(PAGE_SIZE, GFP_KERNEL);
                if (!p)
                        return -ENOMEM;
        }
@@ -94,7 +95,7 @@ static ssize_t trng_read(struct file *file, char __user *ubuf,
        }
 
        if (p != buf)
-               free_page((unsigned long) p);
+               kfree(p);
 
        DEBUG_DBG("trng_read()=%zd\n", ret);
        return ret;