lib/scatterlist: add a flags to signalize mapping direction

sg_miter_start() is currently unaware of the direction of the copy
process (to or from the scatter list). It is important to know the
direction because the page has to be flushed in case the data written
is seen on a different mapping in user land on cache incoherent
architectures.

Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Acked-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Pierre Ossman <pierre@ossman.eu>

1 files changed, 12 insertions, 4 deletions

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index a295e404e908..0d475d8167bf 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -314,6 +314,7 @@ void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
         miter->__sg = sgl;
         miter->__nents = nents;
         miter->__offset = 0;
+        WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG)));
         miter->__flags = flags;
 }
 EXPORT_SYMBOL(sg_miter_start);
@@ -394,6 +395,9 @@ void sg_miter_stop(struct sg_mapping_iter *miter)
         if (miter->addr) {
                 miter->__offset += miter->consumed;
 
+                if (miter->__flags & SG_MITER_TO_SG)
+                        flush_kernel_dcache_page(miter->page);
+
                 if (miter->__flags & SG_MITER_ATOMIC) {
                         WARN_ON(!irqs_disabled());
                         kunmap_atomic(miter->addr, KM_BIO_SRC_IRQ);
@@ -426,8 +430,14 @@ static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
         unsigned int offset = 0;
         struct sg_mapping_iter miter;
         unsigned long flags;
+        unsigned int sg_flags = SG_MITER_ATOMIC;
+
+        if (to_buffer)
+                sg_flags |= SG_MITER_FROM_SG;
+        else
+                sg_flags |= SG_MITER_TO_SG;
 
-        sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC);
+        sg_miter_start(&miter, sgl, nents, sg_flags);
 
         local_irq_save(flags);
 
@@ -438,10 +448,8 @@ static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
 
                 if (to_buffer)
                         memcpy(buf + offset, miter.addr, len);
-                else {
+                else
                         memcpy(miter.addr, buf + offset, len);
-                        flush_kernel_dcache_page(miter.page);
-                }
 
                 offset += len;
         }