[kvm-unit-tests RFC PATCH v2 12/19] arm/arm64: Invalidate TLB before enabling MMU

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Let's invalidate the TLB before enabling the MMU, not after, so we don't
accidently use a stale TLB mapping. For arm, we add a TLBIALL operation,
which applies only to the PE that executed the instruction [1]. For arm64,
we already do that in asm_mmu_enable.

We now find ourselves in a situation where we issue an extra invalidation
after asm_mmu_enable returns. Remove this redundant call to tlb_flush_all.

[1] ARM DDI 0406C.d, section B3.10.6

Reviewed-by: Andrew Jones <drjones@xxxxxxxxxx>
Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
---
Changes:
* Reworded the commit message a bit, but I figured the changes are small and so
  I kept the Reviewed-by.

 lib/arm/mmu.c | 1 -
 arm/cstart.S  | 4 ++++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/arm/mmu.c b/lib/arm/mmu.c
index 161f7a8e607c..66a05d789386 100644
--- a/lib/arm/mmu.c
+++ b/lib/arm/mmu.c
@@ -57,7 +57,6 @@ void mmu_enable(pgd_t *pgtable)
 	struct thread_info *info = current_thread_info();
 
 	asm_mmu_enable(__pa(pgtable));
-	flush_tlb_all();
 
 	info->pgtable = pgtable;
 	mmu_mark_enabled(info->cpu);
diff --git a/arm/cstart.S b/arm/cstart.S
index c8bbb4f0a2a2..748548c3b516 100644
--- a/arm/cstart.S
+++ b/arm/cstart.S
@@ -160,6 +160,10 @@ halt:
 .equ	NMRR,	0xff000004		@ MAIR1 (from Linux kernel)
 .globl asm_mmu_enable
 asm_mmu_enable:
+	/* TLBIALL */
+	mcr	p15, 0, r2, c8, c7, 0
+	dsb	ish
+
 	/* TTBCR */
 	mrc	p15, 0, r2, c2, c0, 2
 	orr	r2, #(1 << 31)		@ TTB_EAE
-- 
2.20.1

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