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powerpc/603: Clear C bit when PTE is read only
On book3s/32 MMU, PP bits don't offer kernel RO protection, kernel pages are always RW. However, on the 603 a page fault is always generated when the C bit (change bit = dirty bit) is not set. Enforce kernel RO protection by clearing C bit in TLB miss handler when the page doesn't have _PAGE_RW flag. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/bbb13848ff0100a76ee9ea95118058c30ae95f2c.1643613343.git.christophe.leroy@csgroup.eu
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@ -507,7 +507,9 @@ DataLoadTLBMiss:
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/* Convert linux-style PTE to low word of PPC-style PTE */
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rlwinm r1,r0,32-9,30,30 /* _PAGE_RW -> PP msb */
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rlwimi r0,r0,32-1,30,30 /* _PAGE_USER -> PP msb */
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rlwimi r1,r0,32-3,24,24 /* _PAGE_RW -> _PAGE_DIRTY */
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rlwimi r0,r0,32-1,31,31 /* _PAGE_USER -> PP lsb */
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xori r1,r1,_PAGE_DIRTY /* clear dirty when not rw */
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ori r1,r1,0xe04 /* clear out reserved bits */
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andc r1,r0,r1 /* PP = user? rw? 1: 3: 0 */
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BEGIN_FTR_SECTION
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