linux-kernel - Re: [PATCH] RISC-V: Show accurate per-hart isa in /proc/cpuinfo

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Message-ID: <20230624-mortally-parking-68f6bc1dd5ee@spud>
Date:   Sat, 24 Jun 2023 01:12:26 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Evan Green <evan@...osinc.com>
Cc:     Palmer Dabbelt <palmer@...osinc.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrew Jones <ajones@...tanamicro.com>,
        Anup Patel <apatel@...tanamicro.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Heiko Stuebner <heiko.stuebner@...ll.eu>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Sunil V L <sunilvl@...tanamicro.com>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH] RISC-V: Show accurate per-hart isa in /proc/cpuinfo

Hey Evan,

On Fri, Jun 23, 2023 at 03:23:53PM -0700, Evan Green wrote:
> In /proc/cpuinfo, most of the information we show for each processor is
> specific to that hart: marchid, mvendorid, mimpid, processor, hart,
> compatible, and the mmu size. But the ISA string gets filtered through a
> lowest common denominator mask, so that if one CPU is missing an ISA
> extension, no CPUs will show it.
> 
> Now that we track the ISA extensions for each hart, let's report ISA
> extension info accurately per-hart in /proc/cpuinfo.

No, you can't do this as it breaks the assumptions of userspace that
this shows the set supported across all harts.
Sorry, but NAK.

Cheers,
Conor.

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