pte_modify fix backport...

From: Daniel J Blueman
Date: Thu Aug 05 2004 - 06:18:47 EST


This patch [1] corrects the behaviour of pte_modify() on ia64 to not
clear page protection flags it shouldn't touch.

Without this patch, it clears the uncacheable flag on UC memory regions,
which can cause MCAs with device I/O.

It was taken into 2.6.0 a while ago, but is yet to be included in 2.4 -
the patch here is rediffed against 2.4.26-rc5.

Is there chance of it being taken in?

--- [1]

diff -durN linux-2.4.26-rc5-orig/include/asm-ia64/pgtable.h linux-2.4.26-rc5-patched/include/asm-ia64/pgtable.h
--- linux-2.4.26-rc5-orig/include/asm-ia64/pgtable.h 2004-02-18 13:36:32.000000000 +0000
+++ linux-2.4.26-rc5-patched/include/asm-ia64/pgtable.h 2004-08-05 11:46:03.000000000 +0100
@@ -60,7 +60,8 @@
#define _PAGE_PROTNONE (__IA64_UL(1) << 63)

#define _PFN_MASK _PAGE_PPN_MASK
-#define _PAGE_CHG_MASK (_PFN_MASK | _PAGE_A | _PAGE_D)
+/* Mask of bits which may be changed by pte_modify(); the odd bits are there for _PAGE_PROTNONE */
+#define _PAGE_CHG_MASK (_PAGE_P | _PAGE_PROTNONE | _PAGE_PL_MASK | _PAGE_AR_MASK | _PAGE_ED)

#define _PAGE_SIZE_4K 12
#define _PAGE_SIZE_8K 13
@@ -216,7 +217,7 @@
({ pte_t __pte; pte_val(__pte) = physpage + pgprot_val(pgprot); __pte; })

#define pte_modify(_pte, newprot) \
- (__pte((pte_val(_pte) & _PAGE_CHG_MASK) | pgprot_val(newprot)))
+ (__pte((pte_val(_pte) & ~_PAGE_CHG_MASK) | (pgprot_val(newprot) & _PAGE_CHG_MASK)))

#define page_pte_prot(page,prot) mk_pte(page, prot)
#define page_pte(page) page_pte_prot(page, __pgprot(0))

--
Daniel J Blueman
Software Engineer, Quadrics Ltd

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