MIPS: mm: Add set_cpu_context() for ASID assignments

When we gain MMID support we'll be storing MMIDs as atomic64_t values
and accessing them via atomic64_* functions. This necessitates that we
don't use cpu_context() as the left hand side of an assignment, ie. as a
modifiable lvalue. In preparation for this introduce a new
set_cpu_context() function & replace all assignments with cpu_context()
on their left hand side with an equivalent call to set_cpu_context().

To enforce that cpu_context() should not be used for assignments, we
rewrite it as a static inline function.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org

arch/mips/include/asm/mmu_context.h

@@ -88,7 +88,17 @@ static inline u64 asid_first_version(unsigned int cpu)
 	return ~asid_version_mask(cpu) + 1;
 }
 
-#define cpu_context(cpu, mm)	((mm)->context.asid[cpu])
+static inline u64 cpu_context(unsigned int cpu, const struct mm_struct *mm)
+{
+	return mm->context.asid[cpu];
+}
+
+static inline void set_cpu_context(unsigned int cpu,
+				   struct mm_struct *mm, u64 ctx)
+{
+	mm->context.asid[cpu] = ctx;
+}
+
 #define asid_cache(cpu)		(cpu_data[cpu].asid_cache)
 #define cpu_asid(cpu, mm) \
 	(cpu_context((cpu), (mm)) & cpu_asid_mask(&cpu_data[cpu]))
@@ -111,7 +121,7 @@ init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 	int i;
 
 	for_each_possible_cpu(i)
-		cpu_context(i, mm) = 0;
+		set_cpu_context(i, mm, 0);
 
 	mm->context.bd_emupage_allocmap = NULL;
 	spin_lock_init(&mm->context.bd_emupage_lock);
@@ -175,7 +185,7 @@ drop_mmu_context(struct mm_struct *mm)
 		htw_start();
 	} else {
 		/* will get a new context next time */
-		cpu_context(cpu, mm) = 0;
+		set_cpu_context(cpu, mm, 0);
 	}
 
 	local_irq_restore(flags);

arch/mips/kernel/smp.c

@@ -537,7 +537,7 @@ void flush_tlb_mm(struct mm_struct *mm)
 
 		for_each_online_cpu(cpu) {
 			if (cpu != smp_processor_id() && cpu_context(cpu, mm))
-				cpu_context(cpu, mm) = 0;
+				set_cpu_context(cpu, mm, 0);
 		}
 	}
 	drop_mmu_context(mm);
@@ -583,7 +583,7 @@ void flush_tlb_range(struct vm_area_struct *vma, unsigned long start, unsigned l
 			 * mm has been completely unused by that CPU.
 			 */
 			if (cpu != smp_processor_id() && cpu_context(cpu, mm))
-				cpu_context(cpu, mm) = !exec;
+				set_cpu_context(cpu, mm, !exec);
 		}
 	}
 	local_flush_tlb_range(vma, start, end);
@@ -635,7 +635,7 @@ void flush_tlb_page(struct vm_area_struct *vma, unsigned long page)
 			 * by that CPU.
 			 */
 			if (cpu != smp_processor_id() && cpu_context(cpu, vma->vm_mm))
-				cpu_context(cpu, vma->vm_mm) = 1;
+				set_cpu_context(cpu, vma->vm_mm, 1);
 		}
 	}
 	local_flush_tlb_page(vma, page);

arch/mips/kvm/emulate.c

@@ -1019,7 +1019,7 @@ static void kvm_mips_change_entryhi(struct kvm_vcpu *vcpu,
 		get_new_mmu_context(kern_mm);
 		for_each_possible_cpu(i)
 			if (i != cpu)
-				cpu_context(i, kern_mm) = 0;
+				set_cpu_context(i, kern_mm, 0);
 		preempt_enable();
 	}
 	kvm_write_c0_guest_entryhi(cop0, entryhi);
@@ -1090,8 +1090,8 @@ static void kvm_mips_invalidate_guest_tlb(struct kvm_vcpu *vcpu,
 		if (i == cpu)
 			continue;
 		if (user)
-			cpu_context(i, user_mm) = 0;
-		cpu_context(i, kern_mm) = 0;
+			set_cpu_context(i, user_mm, 0);
+		set_cpu_context(i, kern_mm, 0);
 	}
 
 	preempt_enable();

arch/mips/kvm/trap_emul.c

@@ -1098,8 +1098,8 @@ static void kvm_trap_emul_check_requests(struct kvm_vcpu *vcpu, int cpu,
 		kvm_mips_flush_gva_pt(kern_mm->pgd, KMF_GPA | KMF_KERN);
 		kvm_mips_flush_gva_pt(user_mm->pgd, KMF_GPA | KMF_USER);
 		for_each_possible_cpu(i) {
-			cpu_context(i, kern_mm) = 0;
-			cpu_context(i, user_mm) = 0;
+			set_cpu_context(i, kern_mm, 0);
+			set_cpu_context(i, user_mm, 0);
 		}
 
 		/* Generate new ASID for current mode */
@@ -1211,7 +1211,7 @@ static void kvm_trap_emul_vcpu_reenter(struct kvm_run *run,
 		if (gasid != vcpu->arch.last_user_gasid) {
 			kvm_mips_flush_gva_pt(user_mm->pgd, KMF_USER);
 			for_each_possible_cpu(i)
-				cpu_context(i, user_mm) = 0;
+				set_cpu_context(i, user_mm, 0);
 			vcpu->arch.last_user_gasid = gasid;
 		}
 	}

arch/mips/mm/context.c

@@ -15,7 +15,8 @@ void get_new_mmu_context(struct mm_struct *mm)
 		local_flush_tlb_all();	/* start new asid cycle */
 	}
 
-	cpu_context(cpu, mm) = asid_cache(cpu) = asid;
+	set_cpu_context(cpu, mm, asid);
+	asid_cache(cpu) = asid;
 }
 
 void check_mmu_context(struct mm_struct *mm)