arm64: mm: Rename asid2idx() to ctxid2asid()

The commit 0c8ea531 ("arm64: mm: Allocate ASIDs in pairs") introduce
the asid2idx and idx2asid macro, but these macros are not really useful
after the commit f88f42f8 ("arm64: context: Free up kernel ASIDs if
KPTI is not in use").

The code "(asid & ~ASID_MASK)" can be instead by a macro, which is the
same code with asid2idx(). So rename it to ctxid2asid() for a better
understanding.

Also we add asid2ctxid() macro, the contextid can be generated based on
the asid and generation through this macro.
Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Link: https://lore.kernel.org/r/c31516eb-6d15-94e0-421c-305fc010ea79@huawei.comSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/context.c

@@ -35,8 +35,8 @@ static unsigned long *pinned_asid_map;
 #define ASID_FIRST_VERSION	(1UL << asid_bits)
 
 #define NUM_USER_ASIDS		ASID_FIRST_VERSION
-#define asid2idx(asid)		((asid) & ~ASID_MASK)
-#define idx2asid(idx)		asid2idx(idx)
+#define ctxid2asid(asid)	((asid) & ~ASID_MASK)
+#define asid2ctxid(asid, genid)	((asid) | (genid))
 
 /* Get the ASIDBits supported by the current CPU */
 static u32 get_cpu_asid_bits(void)
@@ -120,7 +120,7 @@ static void flush_context(void)
 		 */
 		if (asid == 0)
 			asid = per_cpu(reserved_asids, i);
-		__set_bit(asid2idx(asid), asid_map);
+		__set_bit(ctxid2asid(asid), asid_map);
 		per_cpu(reserved_asids, i) = asid;
 	}
 
@@ -162,7 +162,7 @@ static u64 new_context(struct mm_struct *mm)
 	u64 generation = atomic64_read(&asid_generation);
 
 	if (asid != 0) {
-		u64 newasid = generation | (asid & ~ASID_MASK);
+		u64 newasid = asid2ctxid(ctxid2asid(asid), generation);
 
 		/*
 		 * If our current ASID was active during a rollover, we
@@ -183,7 +183,7 @@ static u64 new_context(struct mm_struct *mm)
 		 * We had a valid ASID in a previous life, so try to re-use
 		 * it if possible.
 		 */
-		if (!__test_and_set_bit(asid2idx(asid), asid_map))
+		if (!__test_and_set_bit(ctxid2asid(asid), asid_map))
 			return newasid;
 	}
 
@@ -209,7 +209,7 @@ static u64 new_context(struct mm_struct *mm)
 set_asid:
 	__set_bit(asid, asid_map);
 	cur_idx = asid;
-	return idx2asid(asid) | generation;
+	return asid2ctxid(asid, generation);
 }
 
 void check_and_switch_context(struct mm_struct *mm)
@@ -300,13 +300,13 @@ unsigned long arm64_mm_context_get(struct mm_struct *mm)
 	}
 
 	nr_pinned_asids++;
-	__set_bit(asid2idx(asid), pinned_asid_map);
+	__set_bit(ctxid2asid(asid), pinned_asid_map);
 	refcount_set(&mm->context.pinned, 1);
 
 out_unlock:
 	raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
 
-	asid &= ~ASID_MASK;
+	asid = ctxid2asid(asid);
 
 	/* Set the equivalent of USER_ASID_BIT */
 	if (asid && arm64_kernel_unmapped_at_el0())
@@ -327,7 +327,7 @@ void arm64_mm_context_put(struct mm_struct *mm)
 	raw_spin_lock_irqsave(&cpu_asid_lock, flags);
 
 	if (refcount_dec_and_test(&mm->context.pinned)) {
-		__clear_bit(asid2idx(asid), pinned_asid_map);
+		__clear_bit(ctxid2asid(asid), pinned_asid_map);
 		nr_pinned_asids--;
 	}