linux-kernel - [PATCH v2 2/3] RISC-V: Track ISA extensions per hart

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Message-Id: <20230509182504.2997252-3-evan@rivosinc.com>
Date:   Tue,  9 May 2023 11:25:02 -0700
From:   Evan Green <evan@...osinc.com>
To:     Palmer Dabbelt <palmer@...osinc.com>
Cc:     Evan Green <evan@...osinc.com>,
        Andrew Jones <ajones@...tanamicro.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <apatel@...tanamicro.com>,
        Heiko Stuebner <heiko.stuebner@...ll.eu>,
        Jisheng Zhang <jszhang@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: [PATCH v2 2/3] RISC-V: Track ISA extensions per hart

The kernel maintains a mask of ISA extensions ANDed together across all
harts. Let's also keep a bitmap of ISA extensions for each CPU. Although
the kernel is currently unlikely to enable a feature that exists only on
some CPUs, we want the ability to report asymmetric CPU extensions
accurately to usermode.

Note that riscv_fill_hwcaps() runs before the per_cpu_offsets are built,
which is why I've used a [NR_CPUS] array rather than per_cpu() data.

Signed-off-by: Evan Green <evan@...osinc.com>
Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
Reviewed-by: Palmer Dabbelt <palmer@...osinc.com>
---

Changes in v2:
 - Add blank line before if in riscv_fill_hwcap() (Conor)

 arch/riscv/include/asm/cpufeature.h | 10 ++++++++++
 arch/riscv/kernel/cpufeature.c      | 18 ++++++++++++------
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index 808d5403f2ac..23fed53b8815 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -6,6 +6,9 @@
 #ifndef _ASM_CPUFEATURE_H
 #define _ASM_CPUFEATURE_H
 
+#include <linux/bitmap.h>
+#include <asm/hwcap.h>
+
 /*
  * These are probed via a device_initcall(), via either the SBI or directly
  * from the corresponding CSRs.
@@ -16,8 +19,15 @@ struct riscv_cpuinfo {
 	unsigned long mimpid;
 };
 
+struct riscv_isainfo {
+	DECLARE_BITMAP(isa, RISCV_ISA_EXT_MAX);
+};
+
 DECLARE_PER_CPU(struct riscv_cpuinfo, riscv_cpuinfo);
 
 DECLARE_PER_CPU(long, misaligned_access_speed);
 
+/* Per-cpu ISA extensions. */
+extern struct riscv_isainfo hart_isa[NR_CPUS];
+
 #endif
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index a1954c83638f..e8b7b4b20bb5 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -26,6 +26,9 @@ unsigned long elf_hwcap __read_mostly;
 /* Host ISA bitmap */
 static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
 
+/* Per-cpu ISA extensions. */
+struct riscv_isainfo hart_isa[NR_CPUS];
+
 /* Performance information */
 DEFINE_PER_CPU(long, misaligned_access_speed);
 
@@ -113,14 +116,18 @@ void __init riscv_fill_hwcap(void)
 	bitmap_zero(riscv_isa, RISCV_ISA_EXT_MAX);
 
 	for_each_of_cpu_node(node) {
+		struct riscv_isainfo *isainfo;
 		unsigned long this_hwcap = 0;
-		DECLARE_BITMAP(this_isa, RISCV_ISA_EXT_MAX);
 		const char *temp;
+		unsigned int cpu_id;
 
 		rc = riscv_of_processor_hartid(node, &hartid);
 		if (rc < 0)
 			continue;
 
+		cpu_id = riscv_hartid_to_cpuid(hartid);
+		isainfo = &hart_isa[cpu_id];
+
 		if (of_property_read_string(node, "riscv,isa", &isa)) {
 			pr_warn("Unable to find \"riscv,isa\" devicetree entry\n");
 			continue;
@@ -137,7 +144,6 @@ void __init riscv_fill_hwcap(void)
 		/* The riscv,isa DT property must start with rv64 or rv32 */
 		if (temp == isa)
 			continue;
-		bitmap_zero(this_isa, RISCV_ISA_EXT_MAX);
 		for (; *isa; ++isa) {
 			const char *ext = isa++;
 			const char *ext_end = isa;
@@ -215,7 +221,7 @@ void __init riscv_fill_hwcap(void)
 				if ((ext_end - ext == sizeof(name) - 1) &&	\
 				     !memcmp(ext, name, sizeof(name) - 1) &&	\
 				     riscv_isa_extension_check(bit))		\
-					set_bit(bit, this_isa);			\
+					set_bit(bit, isainfo->isa);		\
 			} while (false)						\
 
 			if (unlikely(ext_err))
@@ -225,7 +231,7 @@ void __init riscv_fill_hwcap(void)
 
 				if (riscv_isa_extension_check(nr)) {
 					this_hwcap |= isa2hwcap[nr];
-					set_bit(nr, this_isa);
+					set_bit(nr, isainfo->isa);
 				}
 			} else {
 				/* sorted alphabetically */
@@ -257,9 +263,9 @@ void __init riscv_fill_hwcap(void)
 			elf_hwcap = this_hwcap;
 
 		if (bitmap_empty(riscv_isa, RISCV_ISA_EXT_MAX))
-			bitmap_copy(riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
+			bitmap_copy(riscv_isa, isainfo->isa, RISCV_ISA_EXT_MAX);
 		else
-			bitmap_and(riscv_isa, riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
+			bitmap_and(riscv_isa, riscv_isa, isainfo->isa, RISCV_ISA_EXT_MAX);
 	}
 
 	/* We don't support systems with F but without D, so mask those out
-- 
2.25.1