[PATCH] arm64: mm: Use asid2idx() and asid feature macro for cleanup

Use asid2idx() and asid feature macro for cleanup.

No functional change.

Signed-off-by: Yunfeng Ye <redacted>
---
 arch/arm64/mm/context.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
index cd72576ae2b7..076f14a75bd5 100644
--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c

@@ -50,10 +50,10 @@ static u32 get_cpu_asid_bits(void)
 		pr_warn("CPU%d: Unknown ASID size (%d); assuming 8-bit\n",
 					smp_processor_id(),  fld);
 		fallthrough;
-	case 0:
+	case ID_AA64MMFR0_ASID_8:
 		asid = 8;
 		break;
-	case 2:
+	case ID_AA64MMFR0_ASID_16:
 		asid = 16;
 	}

@@ -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 = generation | asid2idx(asid);

 		/*
 		 * If our current ASID was active during a rollover, we

@@ -306,7 +306,7 @@ unsigned long arm64_mm_context_get(struct mm_struct *mm)
 out_unlock:
 	raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);

-	asid &= ~ASID_MASK;
+	asid = asid2idx(asid);

 	/* Set the equivalent of USER_ASID_BIT */
 	if (asid && arm64_kernel_unmapped_at_el0())

-- 
2.27.0

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On Thu, Oct 28, 2021 at 08:27:23PM +0800, Yunfeng Ye wrote:

I think this change is fine.

While functionally the code is the same, I don't think this was the
intention of asid2idx(). It's meant to provide an index into asid_map,
while the ASID_MASK lines isolate the asid number and add a new
generation to it.

-- 
Catalin

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On 2021/12/7 0:23, Catalin Marinas wrote:

On Thu, Oct 28, 2021 at 08:27:23PM +0800, Yunfeng Ye wrote:

quoted

Use asid2idx() and asid feature macro for cleanup.

No functional change.

Signed-off-by: Yunfeng Ye <redacted>
---
 arch/arm64/mm/context.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
index cd72576ae2b7..076f14a75bd5 100644
--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c

@@ -50,10 +50,10 @@ static u32 get_cpu_asid_bits(void)
 		pr_warn("CPU%d: Unknown ASID size (%d); assuming 8-bit\n",
 					smp_processor_id(),  fld);
 		fallthrough;
-	case 0:
+	case ID_AA64MMFR0_ASID_8:
 		asid = 8;
 		break;
-	case 2:
+	case ID_AA64MMFR0_ASID_16:
 		asid = 16;
 	}

I think this change is fine.

quoted

@@ -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 = generation | asid2idx(asid);

 		/*
 		 * If our current ASID was active during a rollover, we

@@ -306,7 +306,7 @@ unsigned long arm64_mm_context_get(struct mm_struct *mm)
 out_unlock:
 	raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);

-	asid &= ~ASID_MASK;
+	asid = asid2idx(asid);

While functionally the code is the same, I don't think this was the
intention of asid2idx(). It's meant to provide an index into asid_map,
while the ASID_MASK lines isolate the asid number and add a new
generation to it.

The commit 0c8ea531b774 ("arm64: mm: Allocate ASIDs in pairs") introduce the
asid2idx and idx2asid macro, but these macros is not really useful after the
commit f88f42f853a8 ("arm64: context: Free up kernel ASIDs if KPTI is not in use").

I think "(asid & ~ASID_MASK)" can be instead by a macro, it is the same code with
asid2idx(). Can it be renamed?  (eg, ctxid2asid)

Thanks.


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On Tue, Dec 07, 2021 at 10:21:26AM +0800, Yunfeng Ye wrote:

On 2021/12/7 0:23, Catalin Marinas wrote:

quoted

On Thu, Oct 28, 2021 at 08:27:23PM +0800, Yunfeng Ye wrote:

quoted

@@ -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 = generation | asid2idx(asid);

 		/*
 		 * If our current ASID was active during a rollover, we

@@ -306,7 +306,7 @@ unsigned long arm64_mm_context_get(struct mm_struct *mm)
 out_unlock:
 	raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);

-	asid &= ~ASID_MASK;
+	asid = asid2idx(asid);

While functionally the code is the same, I don't think this was the
intention of asid2idx(). It's meant to provide an index into asid_map,
while the ASID_MASK lines isolate the asid number and add a new
generation to it.

The commit 0c8ea531b774 ("arm64: mm: Allocate ASIDs in pairs") introduce the
asid2idx and idx2asid macro, but these macros is not really useful after the
commit f88f42f853a8 ("arm64: context: Free up kernel ASIDs if KPTI is not in use").

I think "(asid & ~ASID_MASK)" can be instead by a macro, it is the same code with
asid2idx(). Can it be renamed?  (eg, ctxid2asid)

Yes, that would work.

-- 
Catalin

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