linux-kernel - Re: [PATCH v3 3/7] RISC-V: hwprobe: Add support for RISCV_HWPROBE_BASE_BEHAVIOR

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Message-ID: <Y/0zC0Dn9gwC8N5w@spud>
Date:   Mon, 27 Feb 2023 22:47:39 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Evan Green <evan@...osinc.com>
Cc:     Palmer Dabbelt <palmer@...osinc.com>, heiko@...ech.de,
        slewis@...osinc.com, vineetg@...osinc.com,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrew Bresticker <abrestic@...osinc.com>,
        Atish Patra <atishp@...osinc.com>,
        Celeste Liu <coelacanthus@...look.com>,
        Guo Ren <guoren@...nel.org>, Jonathan Corbet <corbet@....net>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v3 3/7] RISC-V: hwprobe: Add support for
 RISCV_HWPROBE_BASE_BEHAVIOR_IMA

Hey Evan,

On Tue, Feb 21, 2023 at 11:08:54AM -0800, Evan Green wrote:
> We have an implicit set of base behaviors that userspace depends on,
> which are mostly defined in various ISA specifications.
> 
> Co-developed-by: Palmer Dabbelt <palmer@...osinc.com>
> Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>
> Signed-off-by: Evan Green <evan@...osinc.com>
> ---
> 
> Changes in v3:
>  - Refactored base ISA behavior probe to allow kernel probing as well,
>    in prep for vDSO data initialization.
>  - Fixed doc warnings in IMA text list, use :c:macro:.
> 
>  Documentation/riscv/hwprobe.rst       | 21 +++++++++++++++++++++
>  arch/riscv/include/asm/hwprobe.h      |  2 +-
>  arch/riscv/include/uapi/asm/hwprobe.h |  5 +++++
>  arch/riscv/kernel/sys_riscv.c         | 20 ++++++++++++++++++++
>  4 files changed, 47 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst
> index 88b015a2026e..9f2da414fbf8 100644
> --- a/Documentation/riscv/hwprobe.rst
> +++ b/Documentation/riscv/hwprobe.rst
> @@ -37,3 +37,24 @@ The following keys are defined:
>    defined by the RISC-V privileged architecture specification.
>  * :c:macro:`RISCV_HWPROBE_KEY_MIMPLID`: Contains the value of ``mimplid``, as
>    defined by the RISC-V privileged architecture specification.
> +* :c:macro:`RISCV_HWPROBE_KEY_BASE_BEHAVIOR`: A bitmask containing the base
> +  user-visible behavior that this kernel supports.  The following base user ABIs
> +  are defined:
> +
> +  * :c:macro:`RISCV_HWPROBE_BASE_BEHAVIOR_IMA`: Support for rv32ima or
> +    rv64ima, as defined by version 2.2 of the user ISA and version 1.10 of the
> +    privileged ISA, with the following known exceptions (more exceptions may be
> +    added, but only if it can be demonstrated that the user ABI is not broken):
> +
> +    * The :fence.i: instruction cannot be directly executed by userspace
> +      programs (it may still be executed in userspace via a
> +      kernel-controlled mechanism such as the vDSO).
> +* :c:macro:`RISCV_HWPROBE_KEY_IMA_EXT_0`: A bitmask containing the extensions
> +  that are compatible with the :c:macro:`RISCV_HWPROBE_BASE_BEHAVIOR_IMA`:
> +  base system behavior.
> +
> +  * :c:macro:`RISCV_HWPROBE_IMA_FD`: The F and D extensions are supported, as
> +    defined by commit cd20cee ("FMIN/FMAX now implement
> +    minimumNumber/maximumNumber, not minNum/maxNum") of the RISC-V ISA manual.
> +  * :c:macro:`RISCV_HWPROBE_IMA_C`: The C extension is supported, as defined
> +    by version 2.2 of the RISC-V ISA manual.

I think I asked for some newlines, but this all seems kinda random now
as to whether there is a blank line between list items or not.

> diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
> index 02c2f1f7417e..f2b224550923 100644
> --- a/arch/riscv/kernel/sys_riscv.c
> +++ b/arch/riscv/kernel/sys_riscv.c
> @@ -9,6 +9,7 @@
>  #include <asm/cacheflush.h>
>  #include <asm/hwprobe.h>
>  #include <asm/sbi.h>
> +#include <asm/switch_to.h>
>  #include <asm/uaccess.h>
>  #include <asm/unistd.h>
>  #include <asm-generic/mman-common.h>
> @@ -124,6 +125,25 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>  	case RISCV_HWPROBE_KEY_MIMPID:
>  		hwprobe_arch_id(pair, cpus);
>  		break;
> +	/*
> +	 * The kernel already assumes that the base single-letter ISA
> +	 * extensions are supported on all harts, and only supports the
> +	 * IMA base, so just cheat a bit here and tell that to
> +	 * userspace.
> +	 */
> +	case RISCV_HWPROBE_KEY_BASE_BEHAVIOR:
> +		pair->value = RISCV_HWPROBE_BASE_BEHAVIOR_IMA;
> +		break;
> +
> +	case RISCV_HWPROBE_KEY_IMA_EXT_0:
> +		pair->value = 0;
> +		if (has_fpu())
> +			pair->value |= RISCV_HWPROBE_IMA_FD;
> +
> +		if (elf_hwcap & RISCV_ISA_EXT_c)
> +			pair->value |= RISCV_HWPROBE_IMA_C;
> +
> +		break;
>  
>  	/*
>  	 * For forward compatibility, unknown keys don't fail the whole

This looks a lot nicer after the refactor, sans the {}.
With a consistent approach taken to newlines:
Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>

Cheers,
Conor.


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