powerpc/44x: Introduce _PAGE_READ and remove _PAGE_USER

44x MMU has 6 page protection bits:
- R, W, X for supervisor
- R, W, X for user

It means that it can support X without R.

To do that, _PAGE_READ flag is needed but there is no bit available
for it in PTE. On the other hand the only real use of _PAGE_USER is
to implement PAGE_NONE by clearing _PAGE_USER.

As _PAGE_NONE can also be implemented by clearing _PAGE_READ,
remove _PAGE_USER and add _PAGE_READ. In order to insert bits in
one go during TLB miss, move _PAGE_ACCESSED and put _PAGE_READ
just after _PAGE_DIRTY so that _PAGE_DIRTY is copied into SW and
_PAGE_READ into SR at once.

With that change, 44x now also honors execute-only protection.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/043e17987b260b99b45094138c6cb2e89e63d499.1695659959.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/nohash/32/pte-44x.h

@@ -63,28 +63,21 @@
  */
 
 #define _PAGE_PRESENT	0x00000001		/* S: PTE valid */
-#define _PAGE_RW	0x00000002		/* S: Write permission */
+#define _PAGE_WRITE	0x00000002		/* S: Write permission */
 #define _PAGE_EXEC	0x00000004		/* H: Execute permission */
-#define _PAGE_ACCESSED	0x00000008		/* S: Page referenced */
+#define _PAGE_READ	0x00000008		/* S: Read permission */
 #define _PAGE_DIRTY	0x00000010		/* S: Page dirty */
 #define _PAGE_SPECIAL	0x00000020		/* S: Special page */
-#define _PAGE_USER	0x00000040		/* S: User page */
+#define _PAGE_ACCESSED	0x00000040		/* S: Page referenced */
 #define _PAGE_ENDIAN	0x00000080		/* H: E bit */
 #define _PAGE_GUARDED	0x00000100		/* H: G bit */
 #define _PAGE_COHERENT	0x00000200		/* H: M bit */
 #define _PAGE_NO_CACHE	0x00000400		/* H: I bit */
 #define _PAGE_WRITETHRU	0x00000800		/* H: W bit */
 
-#define _PAGE_WRITE	_PAGE_RW
-
 /* No page size encoding in the linux PTE */
 #define _PAGE_PSIZE		0
 
-#define _PAGE_KERNEL_RO		0
-#define _PAGE_KERNEL_ROX	_PAGE_EXEC
-#define _PAGE_KERNEL_RW		(_PAGE_DIRTY | _PAGE_RW)
-#define _PAGE_KERNEL_RWX	(_PAGE_DIRTY | _PAGE_RW | _PAGE_EXEC)
-
 /* TODO: Add large page lowmem mapping support */
 #define _PMD_PRESENT	0
 #define _PMD_PRESENT_MASK (PAGE_MASK)
@@ -107,14 +100,7 @@
 #define _PAGE_BASE	(_PAGE_BASE_NC)
 #endif
 
-/* Permission masks used to generate the __P and __S table */
-#define PAGE_NONE	__pgprot(_PAGE_BASE)
-#define PAGE_SHARED	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_RW)
-#define PAGE_SHARED_X	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_RW | _PAGE_EXEC)
-#define PAGE_COPY	__pgprot(_PAGE_BASE | _PAGE_USER)
-#define PAGE_COPY_X	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_EXEC)
-#define PAGE_READONLY	__pgprot(_PAGE_BASE | _PAGE_USER)
-#define PAGE_READONLY_X	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_EXEC)
+#include <asm/pgtable-masks.h>
 
 #endif /* __KERNEL__ */
 #endif /*  _ASM_POWERPC_NOHASH_32_PTE_44x_H */

arch/powerpc/kernel/head_44x.S

@@ -314,8 +314,8 @@ interrupt_base:
 	 * kernel page tables.
 	 */
 	lis	r11, PAGE_OFFSET@h
-	cmplw	r10, r11
-	blt+	3f
+	cmplw	cr7, r10, r11
+	blt+	cr7, 3f
 	lis	r11, swapper_pg_dir@h
 	ori	r11, r11, swapper_pg_dir@l
 
@@ -355,7 +355,7 @@ interrupt_base:
 	 *       place or can we save a couple of instructions here ?
 	 */
 	mfspr	r12,SPRN_ESR
-	li	r13,_PAGE_PRESENT|_PAGE_ACCESSED
+	li	r13,_PAGE_PRESENT|_PAGE_ACCESSED|_PAGE_READ
 	rlwimi	r13,r12,10,30,30
 
 	/* Load the PTE */
@@ -428,8 +428,8 @@ interrupt_base:
 	 * kernel page tables.
 	 */
 	lis	r11, PAGE_OFFSET@h
-	cmplw	r10, r11
-	blt+	3f
+	cmplw	cr7, r10, r11
+	blt+	cr7, 3f
 	lis	r11, swapper_pg_dir@h
 	ori	r11, r11, swapper_pg_dir@l
 
@@ -515,6 +515,7 @@ interrupt_base:
  * 	r11 - PTE high word value
  *	r12 - PTE low word value
  *	r13 - TLB index
+ *	cr7 - Result of comparison with PAGE_OFFSET
  *	MMUCR - loaded with proper value when we get here
  *	Upon exit, we reload everything and RFI.
  */
@@ -533,11 +534,10 @@ finish_tlb_load_44x:
 	tlbwe	r10,r13,PPC44x_TLB_PAGEID	/* Write PAGEID */
 
 	/* And WS 2 */
-	li	r10,0xf85			/* Mask to apply from PTE */
-	rlwimi	r10,r12,29,30,30		/* DIRTY -> SW position */
+	li	r10,0xf84			/* Mask to apply from PTE */
+	rlwimi	r10,r12,29,30,31		/* DIRTY,READ -> SW,SR position */
 	and	r11,r12,r10			/* Mask PTE bits to keep */
-	andi.	r10,r12,_PAGE_USER		/* User page ? */
-	beq	1f				/* nope, leave U bits empty */
+	bge	cr7,1f			/* User page ? no, leave U bits empty */
 	rlwimi	r11,r11,3,26,28			/* yes, copy S bits to U */
 	rlwinm	r11,r11,0,~PPC44x_TLB_SX	/* Clear SX if User page */
 1:	tlbwe	r11,r13,PPC44x_TLB_ATTRIB	/* Write ATTRIB */
@@ -568,8 +568,8 @@ finish_tlb_load_44x:
 	 * kernel page tables.
 	 */
 	lis	r11,PAGE_OFFSET@h
-	cmplw	cr0,r10,r11
-	blt+	3f
+	cmplw	cr7,r10,r11
+	blt+	cr7,3f
 	lis	r11,swapper_pg_dir@h
 	ori	r11,r11, swapper_pg_dir@l
 	li	r12,0			/* MMUCR = 0 */
@@ -599,7 +599,7 @@ finish_tlb_load_44x:
 	 *       place or can we save a couple of instructions here ?
 	 */
 	mfspr	r12,SPRN_ESR
-	li	r13,_PAGE_PRESENT|_PAGE_ACCESSED
+	li	r13,_PAGE_PRESENT|_PAGE_ACCESSED|_PAGE_READ
 	rlwimi	r13,r12,10,30,30
 
 	/* Load the PTE */
@@ -669,8 +669,8 @@ finish_tlb_load_44x:
 	 * kernel page tables.
 	 */
 	lis	r11,PAGE_OFFSET@h
-	cmplw	cr0,r10,r11
-	blt+	3f
+	cmplw	cr7,r10,r11
+	blt+	cr7,3f
 	lis	r11,swapper_pg_dir@h
 	ori	r11,r11, swapper_pg_dir@l
 	li	r12,0			/* MMUCR = 0 */
@@ -744,6 +744,7 @@ finish_tlb_load_44x:
  * 	r11 - PTE high word value
  *	r12 - PTE low word value
  *      r13 - free to use
+ *	cr7 - Result of comparison with PAGE_OFFSET
  *	MMUCR - loaded with proper value when we get here
  *	Upon exit, we reload everything and RFI.
  */
@@ -753,11 +754,10 @@ finish_tlb_load_47x:
 	tlbwe	r11,r13,1
 
 	/* And make up word 2 */
-	li	r10,0xf85			/* Mask to apply from PTE */
-	rlwimi	r10,r12,29,30,30		/* DIRTY -> SW position */
+	li	r10,0xf84			/* Mask to apply from PTE */
+	rlwimi	r10,r12,29,30,31		/* DIRTY,READ -> SW,SR position */
 	and	r11,r12,r10			/* Mask PTE bits to keep */
-	andi.	r10,r12,_PAGE_USER		/* User page ? */
-	beq	1f				/* nope, leave U bits empty */
+	bge	cr7,1f			/* User page ? no, leave U bits empty */
 	rlwimi	r11,r11,3,26,28			/* yes, copy S bits to U */
 	rlwinm	r11,r11,0,~PPC47x_TLB2_SX	/* Clear SX if User page */
 1:	tlbwe	r11,r13,2