linux-kernel - Re: [PATCH 09/15] riscv: implement remote sfence.i natively for M-mode

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Date:   Tue, 20 Aug 2019 21:04:57 +0000
From:   Atish Patra <Atish.Patra@....com>
To:     "hch@....de" <hch@....de>,
        "paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
        "palmer@...ive.com" <palmer@...ive.com>
CC:     "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        Damien Le Moal <Damien.LeMoal@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 09/15] riscv: implement remote sfence.i natively for
 M-mode

On Tue, 2019-08-13 at 17:47 +0200, Christoph Hellwig wrote:
> The RISC-V ISA only supports flushing the instruction cache for the
> local
> CPU core.  For normal S-mode Linux remote flushing is offloaded to
> machine mode using ecalls, but for M-mode Linux we'll have to do it
> ourselves.  Use the same implementation as all the existing open
> source
> SBI implementations by just doing an IPI to all remote cores to
> execute
> th sfence.i instruction on every live core.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  arch/riscv/mm/cacheflush.c | 31 +++++++++++++++++++++++++++----
>  1 file changed, 27 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> index 9ebcff8ba263..10875ea1065e 100644
> --- a/arch/riscv/mm/cacheflush.c
> +++ b/arch/riscv/mm/cacheflush.c
> @@ -10,10 +10,35 @@
>  
>  #include <asm/sbi.h>
>  
> +#ifdef CONFIG_M_MODE
> +static void ipi_remote_fence_i(void *info)
> +{
> +	return local_flush_icache_all();
> +}
> +
> +void flush_icache_all(void)
> +{
> +	on_each_cpu(ipi_remote_fence_i, NULL, 1);
> +}
> +
> +static void flush_icache_cpumask(const cpumask_t *mask)
> +{
> +	on_each_cpu_mask(mask, ipi_remote_fence_i, NULL, 1);
> +}
> +#else /* CONFIG_M_MODE */
>  void flush_icache_all(void)
>  {
>  	sbi_remote_fence_i(NULL);
>  }
> +static void flush_icache_cpumask(const cpumask_t *mask)
> +{
> +	cpumask_t hmask;
> +
> +	cpumask_clear(&hmask);
> +	riscv_cpuid_to_hartid_mask(mask, &hmask);
> +	sbi_remote_fence_i(hmask.bits);
> +}
> +#endif /* CONFIG_M_MODE */
>  
>  /*
>   * Performs an icache flush for the given MM context.  RISC-V has no
> direct
> @@ -28,7 +53,7 @@ void flush_icache_all(void)
>  void flush_icache_mm(struct mm_struct *mm, bool local)
>  {
>  	unsigned int cpu;
> -	cpumask_t others, hmask, *mask;
> +	cpumask_t others, *mask;
>  
>  	preempt_disable();
>  
> @@ -47,9 +72,7 @@ void flush_icache_mm(struct mm_struct *mm, bool
> local)
>  	cpumask_andnot(&others, mm_cpumask(mm), cpumask_of(cpu));
>  	local |= cpumask_empty(&others);
>  	if (mm != current->active_mm || !local) {
> -		cpumask_clear(&hmask);
> -		riscv_cpuid_to_hartid_mask(&others, &hmask);
> -		sbi_remote_fence_i(hmask.bits);
> +		flush_icache_cpumask(&others);
>  	} else {
>  		/*
>  		 * It's assumed that at least one strongly ordered
> operation is

Reviewed-by: Atish Patra <atish.patra@....com>

-- 
Regards,
Atish