scatterlist: replace flush_kernel_dcache_page with flush_dcache_page

Pages used in scatterlist can be mapped page cache pages (and often are),
so we must use flush_dcache_page here instead of the more limited
flush_kernel_dcache_page that is intended for highmem pages only.

Also remove the PageSlab check given that page_mapping_file as used by the
flush_dcache_page implementations already contains that check.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Christoph Hellwig <[e-mail]>
Acked-by: Linus Torvalds <[e-mail]>
Cc: Alex Shi <[e-mail]>
Cc: Geoff Levand <[e-mail]>
Cc: Greentime Hu <[e-mail]>
Cc: Guo Ren <[e-mail]>
Cc: Helge Deller <[e-mail]>
Cc: "James E.J. Bottomley" <[e-mail]>
Cc: Nick Hu <[e-mail]>
Cc: Paul Cercueil <[e-mail]>
Cc: Rich Felker <[e-mail]>
Cc: Russell King <[e-mail]>
Cc: Thomas Bogendoerfer <[e-mail]>
Cc: Ulf Hansson <[e-mail]>
Cc: Vincent Chen <[e-mail]>
Cc: Yoshinori Sato <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

lib/scatterlist.c

···
 		miter->__offset += miter->consumed;
 		miter->__remaining -= miter->consumed;
 
-		if ((miter->__flags & SG_MITER_TO_SG) &&
-		    !PageSlab(miter->page))
-			flush_kernel_dcache_page(miter->page);
+		if (miter->__flags & SG_MITER_TO_SG)
+			flush_dcache_page(miter->page);
 
 		if (miter->__flags & SG_MITER_ATOMIC) {
 			WARN_ON_ONCE(preemptible());