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 b5efec00b671 ("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

1 files changed, 35 insertions, 0 deletions

diff --git a/arch/powerpc/mm/book3s32/mmu_context.c b/arch/powerpc/mm/book3s32/mmu_context.c
index c949363f315f..e2708e387dc3 100644
--- a/arch/powerpc/mm/book3s32/mmu_context.c
+++ b/arch/powerpc/mm/book3s32/mmu_context.c
@@ -24,6 +24,12 @@
 #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
  * hardware supports 24-bit VSIDs, and thus >1 million contexts,
@@ -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);