linux-kernel - Re: [PATCH v3] RISC-V: Fix Maximum Physical Memory 2GiB option for 64bit systems

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Message-ID: <20190405055421.GA7087@infradead.org>
Date:   Thu, 4 Apr 2019 22:54:21 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Anup Patel <Anup.Patel@....com>
Cc:     Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Atish Patra <Atish.Patra@....com>,
        Christoph Hellwig <hch@...radead.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] RISC-V: Fix Maximum Physical Memory 2GiB option for
 64bit systems

On Fri, Apr 05, 2019 at 05:49:34AM +0000, Anup Patel wrote:
> The Maximum Physical Memory 2GiB option for 64bit systems is currently
> broken because kernel hangs at boot-time when this option is enabled
> and the underlying system has more than 2GiB memory.
> 
> This issue can be easily reproduced on SiFive Unleashed board where
> we have 8GiB of memory.
> 
> This patch fixes above issue by removing unusable memory region in
> setup_bootmem().
> 
> Signed-off-by: Anup Patel <anup.patel@....com>
> Reviewed-by: Christoph Hellwig <hch@....de>

Btw, what is the rationale behind even offering the 2GiB option and
the medlow model on 64-bit?  Do we reall have use cases where the
slightly more effient generated code matters so much to keep up
the support burden of this mostly unused and unusual configuration?