linux-kernel - [PATCH v3 5/8] riscv: mm: Use a fixed layout for the MM context ID

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Message-ID: <20231122010815.3545294-6-samuel.holland@sifive.com>
Date:   Tue, 21 Nov 2023 17:07:16 -0800
From:   Samuel Holland <samuel.holland@...ive.com>
To:     Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Alexandre Ghiti <alexghiti@...osinc.com>,
        Samuel Holland <samuel.holland@...ive.com>
Subject: [PATCH v3 5/8] riscv: mm: Use a fixed layout for the MM context ID

Currently, the size of the ASID field in the MM context ID dynamically
depends on the number of hardware-supported ASID bits. This requires
reading a global variable to extract either field from the context ID.
Instead, allocate the maximum possible number of bits to the ASID field,
so the layout of the context ID is known at compile-time.

Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
---

(no changes since v1)

 arch/riscv/include/asm/mmu.h      | 4 ++--
 arch/riscv/include/asm/tlbflush.h | 2 --
 arch/riscv/mm/context.c           | 6 ++----
 3 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h
index a550fbf770be..dc0273f7905f 100644
--- a/arch/riscv/include/asm/mmu.h
+++ b/arch/riscv/include/asm/mmu.h
@@ -26,8 +26,8 @@ typedef struct {
 #endif
 } mm_context_t;
 
-#define cntx2asid(cntx)		((cntx) & asid_mask)
-#define cntx2version(cntx)	((cntx) & ~asid_mask)
+#define cntx2asid(cntx)		((cntx) & SATP_ASID_MASK)
+#define cntx2version(cntx)	((cntx) & ~SATP_ASID_MASK)
 
 void __init create_pgd_mapping(pgd_t *pgdp, uintptr_t va, phys_addr_t pa,
 			       phys_addr_t sz, pgprot_t prot);
diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index 3b393f765805..4448d907f2c9 100644
--- a/arch/riscv/include/asm/tlbflush.h
+++ b/arch/riscv/include/asm/tlbflush.h
@@ -15,8 +15,6 @@
 #define FLUSH_TLB_NO_ASID       ((unsigned long)-1)
 
 #ifdef CONFIG_MMU
-extern unsigned long asid_mask;
-
 static inline void local_flush_tlb_all(void)
 {
 	__asm__ __volatile__ ("sfence.vma" : : : "memory");
diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
index 43d005f63253..b5170ac1b742 100644
--- a/arch/riscv/mm/context.c
+++ b/arch/riscv/mm/context.c
@@ -22,7 +22,6 @@ DEFINE_STATIC_KEY_FALSE(use_asid_allocator);
 
 static unsigned long asid_bits;
 static unsigned long num_asids;
-unsigned long asid_mask;
 
 static atomic_long_t current_version;
 
@@ -128,7 +127,7 @@ static unsigned long __new_context(struct mm_struct *mm)
 		goto set_asid;
 
 	/* We're out of ASIDs, so increment current_version */
-	ver = atomic_long_add_return_relaxed(num_asids, &current_version);
+	ver = atomic_long_add_return_relaxed(BIT(SATP_ASID_BITS), &current_version);
 
 	/* Flush everything  */
 	__flush_context();
@@ -247,7 +246,6 @@ static int __init asids_init(void)
 	/* Pre-compute ASID details */
 	if (asid_bits) {
 		num_asids = 1 << asid_bits;
-		asid_mask = num_asids - 1;
 	}
 
 	/*
@@ -255,7 +253,7 @@ static int __init asids_init(void)
 	 * at-least twice more than CPUs
 	 */
 	if (num_asids > (2 * num_possible_cpus())) {
-		atomic_long_set(&current_version, num_asids);
+		atomic_long_set(&current_version, BIT(SATP_ASID_BITS));
 
 		context_asid_map = bitmap_zalloc(num_asids, GFP_KERNEL);
 		if (!context_asid_map)
-- 
2.42.0