[PATCH v2 2/6] RISC-V: Enable cbo.zero in usermode

[Conor Dooley]

On Wed, Aug 30, 2023 at 06:49:57PM +0200, Andrew Jones wrote:
> When Zicboz is present, enable its instruction (cbo.zero) in
> usermode by setting its respective senvcfg bit. We don't bother
> trying to set this bit per-task, which would also require an
> interface for tasks to request enabling and/or disabling. Instead,
> permanently set the bit for each hart which has the extension when
> bringing it online.
> 
> Signed-off-by: Andrew Jones <ajones at ventanamicro.com>
> ---
>  arch/riscv/include/asm/cpufeature.h |  2 ++
>  arch/riscv/include/asm/csr.h        |  1 +
>  arch/riscv/include/asm/hwcap.h      | 16 ++++++++++++++++
>  arch/riscv/kernel/cpufeature.c      |  6 ++++++
>  arch/riscv/kernel/setup.c           |  4 ++++
>  arch/riscv/kernel/smpboot.c         |  4 ++++
>  6 files changed, 33 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> index 23fed53b8815..788fd575c21a 100644
> --- a/arch/riscv/include/asm/cpufeature.h
> +++ b/arch/riscv/include/asm/cpufeature.h
> @@ -30,4 +30,6 @@ DECLARE_PER_CPU(long, misaligned_access_speed);
>  /* Per-cpu ISA extensions. */
>  extern struct riscv_isainfo hart_isa[NR_CPUS];
>  
> +void riscv_user_isa_enable(void);
> +
>  #endif
> diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
> index 7bac43a3176e..e187e76e3df4 100644
> --- a/arch/riscv/include/asm/csr.h
> +++ b/arch/riscv/include/asm/csr.h
> @@ -273,6 +273,7 @@
>  #define CSR_SIE			0x104
>  #define CSR_STVEC		0x105
>  #define CSR_SCOUNTEREN		0x106
> +#define CSR_SENVCFG		0x10a
>  #define CSR_SSCRATCH		0x140
>  #define CSR_SEPC		0x141
>  #define CSR_SCAUSE		0x142
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index f041bfa7f6a0..66178dbd0045 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -66,6 +66,7 @@
>  #ifndef __ASSEMBLY__
>  
>  #include <linux/jump_label.h>
> +#include <asm/cpufeature.h>
>  
>  unsigned long riscv_get_elf_hwcap(void);
>  
> @@ -130,6 +131,21 @@ riscv_has_extension_unlikely(const unsigned long ext)
>  	return true;
>  }
>  
> +static __always_inline bool riscv_cpu_has_extension_likely(int cpu, const unsigned long ext)
> +{
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) && riscv_has_extension_likely(ext))
> +		return true;

It'd have been nice to put the explanation for this into the commit
message I think, but w/e. Do it if there's a v3 I guess.

Reviewed-by: Conor Dooley <conor.dooley at microchip.com>

Thanks,
Conor.

> +
> +	return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
> +}
> +
> +static __always_inline bool riscv_cpu_has_extension_unlikely(int cpu, const unsigned long ext)
> +{
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) && riscv_has_extension_unlikely(ext))
> +		return true;
> +
> +	return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
> +}
>  #endif
>  
>  #endif /* _ASM_RISCV_HWCAP_H */
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 31843e9cc80c..a33cf7c89d9e 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -391,6 +391,12 @@ unsigned long riscv_get_elf_hwcap(void)
>  	return hwcap;
>  }
>  
> +void riscv_user_isa_enable(void)
> +{
> +	if (riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_ZICBOZ))
> +		csr_set(CSR_SENVCFG, ENVCFG_CBZE);
> +}
> +
>  #ifdef CONFIG_RISCV_ALTERNATIVE
>  /*
>   * Alternative patch sites consider 48 bits when determining when to patch
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 971fe776e2f8..2f053f0763a1 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -25,6 +25,7 @@
>  #include <asm/acpi.h>
>  #include <asm/alternative.h>
>  #include <asm/cacheflush.h>
> +#include <asm/cpufeature.h>
>  #include <asm/cpu_ops.h>
>  #include <asm/early_ioremap.h>
>  #include <asm/pgtable.h>
> @@ -308,9 +309,12 @@ void __init setup_arch(char **cmdline_p)
>  	riscv_fill_hwcap();
>  	init_rt_signal_env();
>  	apply_boot_alternatives();
> +
>  	if (IS_ENABLED(CONFIG_RISCV_ISA_ZICBOM) &&
>  	    riscv_isa_extension_available(NULL, ZICBOM))
>  		riscv_noncoherent_supported();
> +
> +	riscv_user_isa_enable();
>  }
>  
>  static int __init topology_init(void)
> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> index f4d6acb38dd0..502b04abda0b 100644
> --- a/arch/riscv/kernel/smpboot.c
> +++ b/arch/riscv/kernel/smpboot.c
> @@ -25,6 +25,8 @@
>  #include <linux/of.h>
>  #include <linux/sched/task_stack.h>
>  #include <linux/sched/mm.h>
> +
> +#include <asm/cpufeature.h>
>  #include <asm/cpu_ops.h>
>  #include <asm/irq.h>
>  #include <asm/mmu_context.h>
> @@ -252,6 +254,8 @@ asmlinkage __visible void smp_callin(void)
>  			elf_hwcap &= ~COMPAT_HWCAP_ISA_V;
>  	}
>  
> +	riscv_user_isa_enable();
> +
>  	/*
>  	 * Remote TLB flushes are ignored while the CPU is offline, so emit
>  	 * a local TLB flush right now just in case.
> -- 
> 2.41.0
> 
> 
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