linux-kernel - Re: [PATCH v4 03/12] KVM: arm64: guest debug, define API headers

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Date:	Fri, 15 May 2015 17:19:03 +0100
From:	Alex Bennée <alex.bennee@...aro.org>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Peter Maydell <peter.maydell@...aro.org>,
	"kvm\@vger.kernel.org" <kvm@...r.kernel.org>,
	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kvmarm\@lists.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"christoffer.dall\@linaro.org" <christoffer.dall@...aro.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"agraf\@suse.de" <agraf@...e.de>,
	"drjones\@redhat.com" <drjones@...hat.com>,
	"pbonzini\@redhat.com" <pbonzini@...hat.com>,
	"zhichao.huang\@linaro.org" <zhichao.huang@...aro.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"jan.kiszka\@siemens.com" <jan.kiszka@...mens.com>,
	Will Deacon <Will.Deacon@....com>,
	open list <linux-kernel@...r.kernel.org>,
	"dahi\@linux.vnet.ibm.com" <dahi@...ux.vnet.ibm.com>,
	"r65777\@freescale.com" <r65777@...escale.com>,
	"bp\@suse.de" <bp@...e.de>
Subject: Re: [PATCH v4 03/12] KVM: arm64: guest debug, define API headers


Mark Rutland <mark.rutland@....com> writes:

> On Fri, May 15, 2015 at 04:17:46PM +0100, Peter Maydell wrote:
>> On 15 May 2015 at 16:14, Alex Bennée <alex.bennee@...aro.org> wrote:
>> >
>> > Mark Rutland <mark.rutland@....com> writes:
>> >
>> >> On Fri, May 15, 2015 at 03:27:06PM +0100, Alex Bennée wrote:
>> >>> +/*
>> >>> + * See v8 ARM ARM D7.3: Debug Registers
>> >>> + *
>> >>> + * The control registers are architecturally defined as 32 bits but are
>> >>> + * stored as 64 bit values alongside the value registers. This is done
>> >>
>> >> Stale comment? They're stored as __u32 below.
>> >
>> > Gah yes it is.
>> >
>> >> It's possible that the registers could grow in future as happened in the
>> >> case of CLIDR_EL1, so it might be worth treating system registers
>> >> generally as u64 values.
>> >
>> > Really? I mean the existing debug *control* registers have reserved bits
>> > 24-31 so there is space for expansion.
>> 
>> Other places in the userspace ABI which deal with sysregs (notably
>> ONE_REG) consistently define them all as 64-bit
>
> Also for pt_regs.pstate.
>
> I just spotted that in user_hwdebug_state in ptrace.h we seem to expose
> the debug control regsiters as __u32 already, aalong with some other
> registers.

I thought those where ptrace specific fields which then get munged into
the final values inside the kernel?

>
> So we're already inconsistent w.r.t. how we expose those registers, and
> I'm not sure what we'd do elsewhere if any registers got expanded. :/
>
> Mark.

-- 
Alex Bennée
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