Merge tag 'v5.5-rc1' into core/kprobes, to resolve conflicts

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 8 insertions, 6 deletions

diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
index 3bd76e918b5d2..03e01b000f7ac 100644
--- a/drivers/gpu/drm/drm_cache.c
+++ b/drivers/gpu/drm/drm_cache.c
@@ -62,10 +62,10 @@ static void drm_cache_flush_clflush(struct page *pages[],
 {
 	unsigned long i;
 
-	mb();
+	mb(); /*Full memory barrier used before so that CLFLUSH is ordered*/
 	for (i = 0; i < num_pages; i++)
 		drm_clflush_page(*pages++);
-	mb();
+	mb(); /*Also used after CLFLUSH so that all cache is flushed*/
 }
 #endif
 
@@ -92,6 +92,7 @@ drm_clflush_pages(struct page *pages[], unsigned long num_pages)
 
 #elif defined(__powerpc__)
 	unsigned long i;
+
 	for (i = 0; i < num_pages; i++) {
 		struct page *page = pages[i];
 		void *page_virtual;
@@ -125,10 +126,10 @@ drm_clflush_sg(struct sg_table *st)
 	if (static_cpu_has(X86_FEATURE_CLFLUSH)) {
 		struct sg_page_iter sg_iter;
 
-		mb();
+		mb(); /*CLFLUSH is ordered only by using memory barriers*/
 		for_each_sg_page(st->sgl, &sg_iter, st->nents, 0)
 			drm_clflush_page(sg_page_iter_page(&sg_iter));
-		mb();
+		mb(); /*Make sure that all cache line entry is flushed*/
 
 		return;
 	}
@@ -157,12 +158,13 @@ drm_clflush_virt_range(void *addr, unsigned long length)
 	if (static_cpu_has(X86_FEATURE_CLFLUSH)) {
 		const int size = boot_cpu_data.x86_clflush_size;
 		void *end = addr + length;
+
 		addr = (void *)(((unsigned long)addr) & -size);
-		mb();
+		mb(); /*CLFLUSH is only ordered with a full memory barrier*/
 		for (; addr < end; addr += size)
 			clflushopt(addr);
 		clflushopt(end - 1); /* force serialisation */
-		mb();
+		mb(); /*Ensure that evry data cache line entry is flushed*/
 		return;
 	}