[OpenWrt-Devel] [RFC PATCH] kernel: drop MIPS: fix cache flushing for highmem pages

Kevin 'ldir' Darbyshire-Bryant ldir at darbyshire-bryant.me.uk
Tue Dec 18 05:34:35 EST 2018

Signed-off-by: Kevin Darbyshire-Bryant <ldir at darbyshire-bryant.me.uk>

This patch, in a variety of forms, has been around since beginning 2016
as e756c2bb07, ending up in present form 0aa6c7df60 (kernel 4.4.13 bump)
and carried forward ever since.

There have been a number of MIPS kernel memory handling changes since,
including VDSO fixes that meant openwrt patches have been dropped with
no apparent fallout.

I'm basically wondering if this patch needs to still exist in the kernel
4.14.88 world?  I have been running without this patch for 3+ months on
Archer C7 v2 with no obvious ill effects (I'd expect to see "nasty
segfaults and kernel crashes")

If it does still need to exist, should it go upstream?

Thoughts, comments, more testers?

 ...fix-cache-flushing-for-highmem-pages.patch | 30 -------------------
 1 file changed, 30 deletions(-)
 delete mode 100644 target/linux/generic/pending-4.14/100-MIPS-fix-cache-flushing-for-highmem-pages.patch

diff --git a/target/linux/generic/pending-4.14/100-MIPS-fix-cache-flushing-for-highmem-pages.patch b/target/linux/generic/pending-4.14/100-MIPS-fix-cache-flushing-for-highmem-pages.patch
deleted file mode 100644
index b1c65f7cd8..0000000000
--- a/target/linux/generic/pending-4.14/100-MIPS-fix-cache-flushing-for-highmem-pages.patch
+++ /dev/null
@@ -1,30 +0,0 @@
-From: Felix Fietkau <nbd at nbd.name>
-Subject: MIPS: fix cache flushing for highmem pages
-Most cache flush ops were no-op for highmem pages. This led to nasty
-segfaults and (in the case of page_address(page) == NULL) kernel
-Fix this by always flushing highmem pages using kmap/kunmap_atomic
-around the actual cache flush. This might be a bit inefficient, but at
-least it's stable.
-Signed-off-by: Felix Fietkau <nbd at nbd.name>
---- a/arch/mips/mm/cache.c
-+++ b/arch/mips/mm/cache.c
-@@ -116,6 +116,13 @@ void __flush_anon_page(struct page *page
- {
- 	unsigned long addr = (unsigned long) page_address(page);
-+	if (PageHighMem(page)) {
-+		addr = (unsigned long)kmap_atomic(page);
-+		flush_data_cache_page(addr);
-+		__kunmap_atomic((void *)addr);
-+		return;
-+	}
- 	if (pages_do_alias(addr, vmaddr)) {
- 		if (page_mapcount(page) && !Page_dcache_dirty(page)) {
- 			void *kaddr;
2.17.2 (Apple Git-113)

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