[PATCH v2] riscv: hwprobe: export largest userspace address

[Conor Dooley]

On Tue, Feb 20, 2024 at 12:09:46PM +0100, Clément Léger 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=svxx" 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.
> 
> 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 at rivosinc.com>

Doesn't build for nommu:
https://patchwork.kernel.org/project/linux-riscv/patch/20240220110950.871307-1-cleger@rivosinc.com/

Cheers,
Conor.
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