Patch "MIPS: Flush highmem pages in __flush_dcache_page" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

MIPS: Flush highmem pages in __flush_dcache_page

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mips-flush-highmem-pages-in-__flush_dcache_page.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Paul Burton <[email protected]>
Date: Tue, 1 Mar 2016 02:37:57 +0000
Subject: MIPS: Flush highmem pages in __flush_dcache_page

From: Paul Burton <[email protected]>

commit 234859e49a15323cf1b2331bdde7f658c4cb45fb upstream.

When flush_dcache_page is called on an executable page, that page is about to be provided to userland & we can presume that the icache contains no valid entries for its address range. However if the icache does not fill from the dcache then we cannot presume that the pages content has been written back as far as the memories that the dcache will fill from (ie. L2 or further out).

This was being done for lowmem pages, but not for highmem which can lead to icache corruption. Fix this by mapping highmem pages & flushing their content from the dcache in __flush_dcache_page before providing the page to userland, just as is done for lowmem pages.

Patchwork: https://patchwork.linux-mips.org/patch/12720/

---
 arch/mips/mm/cache.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

@@ -16,6 +16,7 @@
 #include <linux/mm.h>
 
 #include <asm/cacheflush.h>
+#include <asm/highmem.h>
 #include <asm/processor.h>
 #include <asm/cpu.h>
 #include <asm/cpu-features.h>

@@ -83,8 +84,6 @@ void __flush_dcache_page(struct page *pa
 	struct address_space *mapping = page_mapping(page);
 	unsigned long addr;
 
-	if (PageHighMem(page))
-		return;
 	if (mapping && !mapping_mapped(mapping)) {
 		SetPageDcacheDirty(page);
 		return;

@@ -95,8 +94,15 @@ void __flush_dcache_page(struct page *pa
 	 * case is for exec env/arg pages and those are %99 certainly going to
 	 * get faulted into the tlb (and thus flushed) anyways.
 	 */
-	addr = (unsigned long) page_address(page);
+	if (PageHighMem(page))
+		addr = (unsigned long)kmap_atomic(page);
+	else
+		addr = (unsigned long)page_address(page);
+
 	flush_data_cache_page(addr);
+
+	if (PageHighMem(page))
+		__kunmap_atomic((void *)addr);
 }
 
 EXPORT_SYMBOL(__flush_dcache_page);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/mips-disable-preemption-during-prctl-pr_set_fp_mode.patch queue-4.4/mips-flush-highmem-pages-in-__flush_dcache_page.patch queue-4.4/mips-fix-sigreturn-via-vdso-on-micromips-kernel.patch queue-4.4/mips-handle-highmem-pages-in-__update_cache.patch queue-4.4/mips-fix-watchpoint-restoration.patch queue-4.4/mips-build-micromips-vdso-for-micromips-kernels.patch queue-4.4/mips-math-emu-fix-jalr-emulation-when-rd-0.patch queue-4.4/mips-sync-icache-dcache-in-set_pte_at.patch queue-4.4/mips-fix-msa-ld_-st_-asm-macros-to-use-ptr_addu.patch queue-4.4/mips-prevent-restoration-of-msa-context-in-non-msa-kernels.patch queue-4.4/mips-use-copy_s.fmt-rather-than-copy_u.fmt.patch