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Date: Wed, 21 Feb 2024 14:51:46 +0000
From: Conor Dooley <conor@kernel.org>
To: =?iso-8859-1?Q?Cl=E9ment_L=E9ger?= <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>,
	Charlie Jenkins <charlie@rivosinc.com>,
	Stefan O'Rear <sorear@fastmail.com>,
	Jessica Clarke <jrtc27@jrtc27.com>
Subject: Re: [PATCH v2] riscv: hwprobe: export largest userspace address
Message-ID: <20240221-pacifism-seismic-589dbbcbf38b@spud>
References: <20240220110950.871307-1-cleger@rivosinc.com>
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On Tue, Feb 20, 2024 at 12:09:46PM +0100, Cl=E9ment L=E9ger wrote:
> Some userspace applications (OpenJDK for instance) uses the free MSBs
> in pointers to insert additional information for their own logic and
> need to get this information from somewhere. Currently they rely on
> parsing /proc/cpuinfo "mmu=3Dsvxx" string to obtain the current value of
> virtual address used bits [1]. Since this reflect the raw MMU mode
> supported, it might differ from the logical one used internally.
> Exporting the maximum mmappable address through hwprobe will allow a
> more stable interface to be used. For that purpose, add a new hwprobe
> key named RISCV_HWPROBE_MAX_KEY which will export the maximum mmappable
> userspace address.
>=20
> Link: https://github.com/openjdk/jdk/blob/master/src/hotspot/os_cpu/linux=
_riscv/vm_version_linux_riscv.cpp#L171 [1]
> Signed-off-by: Cl=E9ment L=E9ger <cleger@rivosinc.com>

Doesn't build for nommu:
https://patchwork.kernel.org/project/linux-riscv/patch/20240220110950.87130=
7-1-cleger@rivosinc.com/

Cheers,
Conor.

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