linux-kernel - Re: [RFC][PATCH] arm64: Add support for CONFIG_DEBUG

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Date:   Fri, 28 Oct 2016 12:11:46 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Laura Abbott <labbott@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] arm64: Add support for CONFIG_DEBUG_VIRTUAL

On Fri, Oct 28, 2016 at 08:52:50AM +0100, Ard Biesheuvel wrote:
> Hi Laura,
> 
> On 28 October 2016 at 01:18, Laura Abbott <labbott@...hat.com> wrote:
> > x86 has an option CONFIG_DEBUG_VIRTUAL to do additional checks
> > on virt_to_phys calls. The goal is to catch users who are calling
> > virt_to_phys on non-linear addresses immediately. As features
> > such as CONFIG_VMAP_STACK get enabled for arm64, this becomes
> > increasingly important. Add checks to catch bad virt_to_phys
> > usage.
> 
> I think this is a useful thing to have. However, the Kconfig
> description talks about virt to page translations, not virt to phys.
> Of course, this is a shift away from being equivalent on x86, but not
> so much on arm64. Any concerns there?

See commit 59ea746337c69f6a ("MM: virtual address debug"); the existing
x86 cases cover virt to phys also.

The Kconfig text does say "and friends"...

Thanks,
Mark.