powerpc/603: Inconditionally use task PGDIR in ITLB misses

Now that modules exec page tables are preallocated, the instruction
TLBmiss handler can use task PGDIR inconditionally.

Also revise the identification of user vs kernel user space by doing
a calculation instead of a comparison: Get the segment number and
subtract the number of the first kernel segment. The result is
positive for kernel addresses and negative for user addresses,
which means that upper 2 bits are 0 for kernel and 3 for user.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/9a3242162ad2faab8019c698e501b326a126ee9e.1724173828.git.christophe.leroy@csgroup.eu

Author: chleroy

arch/powerpc/kernel/head_book3s_32.S

@@ -413,22 +413,15 @@ END_FTR_SECTION_IFSET(CPU_FTR_FPU_UNAVAILABLE)
 InstructionTLBMiss:
 	/* Get PTE (linux-style) and check access */
 	mfspr	r0,SPRN_IMISS
-#ifdef CONFIG_EXECMEM
-	lis	r1, TASK_SIZE@h		/* check if kernel address */
-	cmplw	0,r1,r0
-#endif
 	mfspr	r2, SPRN_SDR1
 	li	r1,_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_EXEC
 	rlwinm	r2, r2, 28, 0xfffff000
+	rlwimi	r2,r0,12,20,29		/* insert top 10 bits of address */
+	lwz	r2,0(r2)		/* get pmd entry */
 #ifdef CONFIG_EXECMEM
-	li	r3, 3
-	bgt-	112f
-	lis	r2, (swapper_pg_dir - PAGE_OFFSET)@ha	/* if kernel address, use */
-	li	r3, 0
-	addi	r2, r2, (swapper_pg_dir - PAGE_OFFSET)@l	/* kernel page table */
+	rlwinm	r3, r0, 4, 0xf
+	subi	r3, r3, (TASK_SIZE >> 28) & 0xf
 #endif
-112:	rlwimi	r2,r0,12,20,29		/* insert top 10 bits of address */
-	lwz	r2,0(r2)		/* get pmd entry */
 	rlwinm.	r2,r2,0,0,19		/* extract address of pte page */
 	beq-	InstructionAddressInvalid	/* return if no mapping */
 	rlwimi	r2,r0,22,20,29		/* insert next 10 bits of address */
@@ -437,7 +430,7 @@ InstructionTLBMiss:
 	bne-	InstructionAddressInvalid /* return if access not permitted */
 	/* Convert linux-style PTE to low word of PPC-style PTE */
 #ifdef CONFIG_EXECMEM
-	rlwimi	r2, r3, 0, 31, 31	/* userspace ? -> PP lsb */
+	rlwimi	r2, r3, 1, 31, 31	/* userspace ? -> PP lsb */
 #endif
 	ori	r1, r1, 0xe06		/* clear out reserved bits */
 	andc	r1, r2, r1		/* PP = user? 1 : 0 */