linux-kernel - Re: [PATCH v6 3/3] arm64: kexec

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Date:   Fri, 28 Jun 2019 19:47:20 +0800
From:   Hsin-Yi Wang <hsinyi@...omium.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Miles Chen <miles.chen@...iatek.com>,
        James Morse <james.morse@....com>,
        Andrew Murray <andrew.murray@....com>,
        Jun Yao <yaojun8558363@...il.com>, Yu Zhao <yuzhao@...gle.com>,
        Robin Murphy <robin.murphy@....com>,
        Laura Abbott <labbott@...hat.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v6 3/3] arm64: kexec_file: add rng-seed support

On Fri, Jun 28, 2019 at 5:42 PM Mark Rutland <mark.rutland@....com> wrote:
>
> On Wed, Jun 12, 2019 at 12:33:02PM +0800, Hsin-Yi Wang wrote:
> > Adding "rng-seed" to dtb. It's fine to add this property if original
> > fdt doesn't contain it. Since original seed will be wiped after
> > read, so use a default size 128 bytes here.
>
> Why is 128 bytes the default value?
More than 64 bytes should be enough.
>
> I didn't see an update to Documentation/devicetree/bindings/chosen.txt,
> so it's not clear to me precisely what we expect.
>
Rob suggested to update in a newer dt-schema documentation at
https://github.com/devicetree-org/dt-schema.
A pull request has been sent but perhaps it would continue if kernel
patches are accepted.
>
> For 128 bytes, it would be better to use a buffer on the stack. That
> avoids the possibility of the allocation failing.
>
Okay, I'll update this.
>
> If the RNG wasn't initialised, we'd carry on with a warning. Why do we
> follow a different policy here?
>
For failure case, I think kernel can still be boot since this is not a
very fatal case, just same as the seed wasn't provided by bootloader
at first boot. So I'll also let fdt_setprop() failed case carry on
with warning.

Thanks