From: Charlie Jenkins <charlie@rivosinc.com>
To: "Clément Léger" <cleger@rivosinc.com>
Cc: Jonathan Corbet <corbet@lwn.net>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
linux-doc@vger.kernel.org, linux-riscv@lists.infradead.org,
linux-kernel@vger.kernel.org, Robin Ehn <rehn@rivosinc.com>
Subject: Re: [PATCH] riscv: hwprobe: export VA_BITS
Date: Thu, 1 Feb 2024 18:32:50 -0800 [thread overview]
Message-ID: <ZbxUUsKdKIPI8Fb/@ghost> (raw)
In-Reply-To: <20240201140319.360088-1-cleger@rivosinc.com>
On Thu, Feb 01, 2024 at 03:02:45PM +0100, Clément Léger wrote:
> Some userspace applications (OpenJDK for instance) uses the free bits
> in pointers to insert additional information for their own logic.
> Currently they rely on parsing /proc/cpuinfo to obtain the current value
> of virtual address used bits [1]. Exporting VA_BITS through hwprobe will
> allow for a more stable interface to be used.
mmap already supports this without a need for applications to know the
underlying hardware. If a hint address is passed into mmap, it will never
return an address that uses more bits than the hint address. I designed
it that way so that something like this wasn't necessary.
- Charlie
>
> Link: https://github.com/openjdk/jdk/blob/master/src/hotspot/os_cpu/linux_riscv/vm_version_linux_riscv.cpp#L171 [1]
> Signed-off-by: Clément Léger <cleger@rivosinc.com>
>
> ---
> Documentation/arch/riscv/hwprobe.rst | 3 +++
> arch/riscv/include/asm/hwprobe.h | 2 +-
> arch/riscv/include/uapi/asm/hwprobe.h | 1 +
> arch/riscv/kernel/sys_hwprobe.c | 3 +++
> 4 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
> index b2bcc9eed9aa..6f198c6ed4f0 100644
> --- a/Documentation/arch/riscv/hwprobe.rst
> +++ b/Documentation/arch/riscv/hwprobe.rst
> @@ -210,3 +210,6 @@ The following keys are defined:
>
> * :c:macro:`RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE`: An unsigned int which
> represents the size of the Zicboz block in bytes.
> +
> +* :c:macro:`RISCV_HWPROBE_KEY_VA_BITS`: An unsigned long which
> + represent the number of bits used to store virtual addresses.
> diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
> index 630507dff5ea..150a9877b0af 100644
> --- a/arch/riscv/include/asm/hwprobe.h
> +++ b/arch/riscv/include/asm/hwprobe.h
> @@ -8,7 +8,7 @@
>
> #include <uapi/asm/hwprobe.h>
>
> -#define RISCV_HWPROBE_MAX_KEY 6
> +#define RISCV_HWPROBE_MAX_KEY 7
>
> static inline bool riscv_hwprobe_key_is_valid(__s64 key)
> {
> diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
> index 9f2a8e3ff204..2a5006cddb7b 100644
> --- a/arch/riscv/include/uapi/asm/hwprobe.h
> +++ b/arch/riscv/include/uapi/asm/hwprobe.h
> @@ -67,6 +67,7 @@ struct riscv_hwprobe {
> #define RISCV_HWPROBE_MISALIGNED_UNSUPPORTED (4 << 0)
> #define RISCV_HWPROBE_MISALIGNED_MASK (7 << 0)
> #define RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE 6
> +#define RISCV_HWPROBE_KEY_VA_BITS 7
> /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */
>
> /* Flags */
> diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
> index a7c56b41efd2..328435836e36 100644
> --- a/arch/riscv/kernel/sys_hwprobe.c
> +++ b/arch/riscv/kernel/sys_hwprobe.c
> @@ -202,6 +202,9 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
> if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOZ))
> pair->value = riscv_cboz_block_size;
> break;
> + case RISCV_HWPROBE_KEY_VA_BITS:
> + pair->value = VA_BITS;
> + break;
>
> /*
> * For forward compatibility, unknown keys don't fail the whole
> --
> 2.43.0
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
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next prev parent reply other threads:[~2024-02-02 2:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-01 14:02 [PATCH] riscv: hwprobe: export VA_BITS Clément Léger
2024-02-02 2:32 ` Charlie Jenkins [this message]
2024-02-02 8:22 ` Clément Léger
2024-02-03 10:40 ` Stefan O'Rear
2024-02-04 0:22 ` Jessica Clarke
2024-02-06 9:24 ` Clément Léger
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