linux-kernel - Re: [PATCH v2] riscv: mm: don't advertise 1 num

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Date:   Sun, 03 Oct 2021 10:10:09 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     vgupta@...nel.org
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        Anup Patel <Anup.Patel@....com>, jszhang@...nel.org,
        guoren@...ux.alibaba.com, wangkefeng.wang@...wei.com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        vgupta@...nel.org, anup@...infault.org
Subject:     Re: [PATCH v2] riscv: mm: don't advertise 1 num_asid for 0 asid bits

On Wed, 08 Sep 2021 10:30:29 PDT (-0700), vgupta@...nel.org wrote:
> Even if mmu doesn't support ASID, current code calculates @num_asids=1
> which is misleading, so avoid setting any asid related variables in such
> case.
>
> Also while here, print the number of asid bits discovered even for the
> disabled case.
>
> Verified this on Hifive Unmatched.
>
> Reviewed-by: Anup Patel <anup@...infault.org>
> Signed-off-by: Vineet Gupta <vgupta@...nel.org>
> ---
>  arch/riscv/mm/context.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
> index ee3459cb6750..ea54cc0c9106 100644
> --- a/arch/riscv/mm/context.c
> +++ b/arch/riscv/mm/context.c
> @@ -233,8 +233,10 @@ static int __init asids_init(void)
>  	local_flush_tlb_all();
>
>  	/* Pre-compute ASID details */
> -	num_asids = 1 << asid_bits;
> -	asid_mask = num_asids - 1;
> +	if (asid_bits) {
> +		num_asids = 1 << asid_bits;
> +		asid_mask = num_asids - 1;
> +	}
>
>  	/*
>  	 * Use ASID allocator only if number of HW ASIDs are
> @@ -255,7 +257,7 @@ static int __init asids_init(void)
>  		pr_info("ASID allocator using %lu bits (%lu entries)\n",
>  			asid_bits, num_asids);
>  	} else {
> -		pr_info("ASID allocator disabled\n");
> +		pr_info("ASID allocator disabled (%lu bits)\n", asid_bits);
>  	}
>
>  	return 0;

Thanks, this is on for-next.