[RFC PATCH 5/9] riscv: Split per-CPU and per-thread envcfg bits

[Samuel Holland]

Some envcfg bits need to be controlled on a per-thread basis, such as
the pointer masking mode. However, the envcfg CSR value cannot simply be
stored in struct thread_struct, because some hardware may implement a
different subset of envcfg CSR bits is across CPUs. As a result, we need
to combine the per-CPU and per-thread bits whenever we switch threads.

Signed-off-by: Samuel Holland <samuel.holland at sifive.com>
---

 arch/riscv/include/asm/cpufeature.h |  2 ++
 arch/riscv/include/asm/processor.h  |  1 +
 arch/riscv/include/asm/switch_to.h  | 12 ++++++++++++
 arch/riscv/kernel/cpufeature.c      |  4 +++-
 4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index 0bd11862b760..b1ad8d0b4599 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -33,6 +33,8 @@ DECLARE_PER_CPU(long, misaligned_access_speed);
 /* Per-cpu ISA extensions. */
 extern struct riscv_isainfo hart_isa[NR_CPUS];
 
+DECLARE_PER_CPU(unsigned long, riscv_cpu_envcfg);
+
 void riscv_user_isa_enable(void);
 
 #ifdef CONFIG_RISCV_MISALIGNED
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index a8509cc31ab2..06b87402a4d8 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -118,6 +118,7 @@ struct thread_struct {
 	unsigned long s[12];	/* s[0]: frame pointer */
 	struct __riscv_d_ext_state fstate;
 	unsigned long bad_cause;
+	unsigned long envcfg;
 	u32 riscv_v_flags;
 	u32 vstate_ctrl;
 	struct __riscv_v_ext_state vstate;
diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index 7efdb0584d47..256a354a5c4a 100644
--- a/arch/riscv/include/asm/switch_to.h
+++ b/arch/riscv/include/asm/switch_to.h
@@ -69,6 +69,17 @@ static __always_inline bool has_fpu(void) { return false; }
 #define __switch_to_fpu(__prev, __next) do { } while (0)
 #endif
 
+static inline void sync_envcfg(struct task_struct *task)
+{
+	csr_write(CSR_ENVCFG, this_cpu_read(riscv_cpu_envcfg) | task->thread.envcfg);
+}
+
+static inline void __switch_to_envcfg(struct task_struct *next)
+{
+	if (riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_XLINUXENVCFG))
+		sync_envcfg(next);
+}
+
 extern struct task_struct *__switch_to(struct task_struct *,
 				       struct task_struct *);
 
@@ -80,6 +91,7 @@ do {							\
 		__switch_to_fpu(__prev, __next);	\
 	if (has_vector())					\
 		__switch_to_vector(__prev, __next);	\
+	__switch_to_envcfg(__next);			\
 	((last) = __switch_to(__prev, __next));		\
 } while (0)
 
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index d1846aab1f78..32aaaf41f8a8 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -44,6 +44,8 @@ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
 /* Per-cpu ISA extensions. */
 struct riscv_isainfo hart_isa[NR_CPUS];
 
+DEFINE_PER_CPU(unsigned long, riscv_cpu_envcfg);
+
 /* Performance information */
 DEFINE_PER_CPU(long, misaligned_access_speed);
 
@@ -978,7 +980,7 @@ arch_initcall(check_unaligned_access_all_cpus);
 void riscv_user_isa_enable(void)
 {
 	if (riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_ZICBOZ))
-		csr_set(CSR_ENVCFG, ENVCFG_CBZE);
+		this_cpu_or(riscv_cpu_envcfg, ENVCFG_CBZE);
 }
 
 #ifdef CONFIG_RISCV_ALTERNATIVE
-- 
2.43.1