powerpc/32s: Convert switch_mmu_context() to C

switch_mmu_context() does things that can easily be done in C.

For updating user segments, we have update_user_segments().

As mentionned in commit b5efec00 ("powerpc/32s: Move KUEP
locking/unlocking in C"), update_user_segments() has the loop
unrolled which is a significant performance gain.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/05c0875ad8220c03452c3a334946e207c6ca04d6.1622708530.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/book3s/32/kup.h

@@ -7,6 +7,11 @@
 
 #ifndef __ASSEMBLY__
 
+static __always_inline bool kuap_is_disabled(void)
+{
+	return !IS_ENABLED(CONFIG_PPC_KUAP);
+}
+
 static __always_inline bool kuep_is_disabled(void)
 {
 	return !IS_ENABLED(CONFIG_PPC_KUEP);

arch/powerpc/kernel/asm-offsets.c

@@ -86,7 +86,6 @@ int main(void)
 	OFFSET(PACA_CANARY, paca_struct, canary);
 #endif
 #endif
-	OFFSET(MMCONTEXTID, mm_struct, context.id);
 #ifdef CONFIG_PPC32
 #ifdef CONFIG_PPC_RTAS
 	OFFSET(RTAS_SP, thread_struct, rtas_sp);
@@ -323,10 +322,6 @@ int main(void)
 #endif
 #endif
 
-#ifndef CONFIG_PPC64
-	OFFSET(MM_PGD, mm_struct, pgd);
-#endif /* ! CONFIG_PPC64 */
-
 	/* About the CPU features table */
 	OFFSET(CPU_SPEC_FEATURES, cpu_spec, cpu_features);
 	OFFSET(CPU_SPEC_SETUP, cpu_spec, cpu_setup);

arch/powerpc/kernel/head_book3s_32.S

@@ -1033,58 +1033,6 @@ END_MMU_FTR_SECTION_IFCLR(MMU_FTR_HPTE_TABLE)
 	mtspr	SPRN_SRR1,r4
 	rfi
 
-/*
- * void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next);
- *
- * Set up the segment registers for a new context.
- */
-_ENTRY(switch_mmu_context)
-	lwz	r3,MMCONTEXTID(r4)
-	cmpwi	cr0,r3,0
-	blt-	4f
-	mulli	r3,r3,897	/* multiply context by skew factor */
-	rlwinm	r3,r3,4,8,27	/* VSID = (context & 0xfffff) << 4 */
-#ifdef CONFIG_PPC_KUEP
-	oris	r3, r3, SR_NX@h	/* Set Nx */
-#endif
-#ifdef CONFIG_PPC_KUAP
-	oris	r3, r3, SR_KS@h	/* Set Ks */
-#endif
-	li	r0,NUM_USER_SEGMENTS
-	mtctr	r0
-
-#ifdef CONFIG_BDI_SWITCH
-	/* Context switch the PTE pointer for the Abatron BDI2000.
-	 * The PGDIR is passed as second argument.
-	 */
-	lwz	r4, MM_PGD(r4)
-	lis	r5, abatron_pteptrs@ha
-	stw	r4, abatron_pteptrs@l + 0x4(r5)
-#endif
-BEGIN_MMU_FTR_SECTION
-#ifndef CONFIG_BDI_SWITCH
-	lwz	r4, MM_PGD(r4)
-#endif
-	tophys(r4, r4)
-	rlwinm	r4, r4, 4, 0xffff01ff
-	mtspr	SPRN_SDR1, r4
-END_MMU_FTR_SECTION_IFCLR(MMU_FTR_HPTE_TABLE)
-	li	r4,0
-	isync
-3:
-	mtsrin	r3,r4
-	addi	r3,r3,0x111	/* next VSID */
-	rlwinm	r3,r3,0,8,3	/* clear out any overflow from VSID field */
-	addis	r4,r4,0x1000	/* address of next segment */
-	bdnz	3b
-	sync
-	isync
-	blr
-4:	trap
-	EMIT_BUG_ENTRY 4b,__FILE__,__LINE__,0
-	blr
-EXPORT_SYMBOL(switch_mmu_context)
-
 /*
  * An undocumented "feature" of 604e requires that the v bit
  * be cleared before changing BAT values.
@@ -1282,9 +1230,3 @@ EXPORT_SYMBOL(empty_zero_page)
 	.globl	swapper_pg_dir
 swapper_pg_dir:
 	.space	PGD_TABLE_SIZE
-
-/* Room for two PTE pointers, usually the kernel and current user pointers
- * to their respective root page table.
- */
-abatron_pteptrs:
-	.space	8

arch/powerpc/mm/book3s32/mmu_context.c

@@ -23,6 +23,12 @@
 
 #include <asm/mmu_context.h>
 
+/*
+ * Room for two PTE pointers, usually the kernel and current user pointers
+ * to their respective root page table.
+ */
+void *abatron_pteptrs[2];
+
 /*
  * On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs
  * (virtual segment identifiers) for each context.  Although the
@@ -98,3 +104,32 @@ void __init mmu_context_init(void)
 	context_map[0] = (1 << FIRST_CONTEXT) - 1;
 	next_mmu_context = FIRST_CONTEXT;
 }
+
+void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next, struct task_struct *tsk)
+{
+	long id = next->context.id;
+	unsigned long val;
+
+	if (id < 0)
+		panic("mm_struct %p has no context ID", next);
+
+	isync();
+
+	val = CTX_TO_VSID(id, 0);
+	if (!kuep_is_disabled())
+		val |= SR_NX;
+	if (!kuap_is_disabled())
+		val |= SR_KS;
+
+	update_user_segments(val);
+
+	if (IS_ENABLED(CONFIG_BDI_SWITCH))
+		abatron_pteptrs[1] = next->pgd;
+
+	if (!mmu_has_feature(MMU_FTR_HPTE_TABLE))
+		mtspr(SPRN_SDR1, rol32(__pa(next->pgd), 4) & 0xffff01ff);
+
+	mb();	/* sync */
+	isync();
+}
+EXPORT_SYMBOL(switch_mmu_context);