linux-kernel - Re: Re: [RESEND PATCH v5 5/5] Documentation/vmcoreinfo: Add documentation for 'TCR

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Message-ID: <CACi5LpPXdcJ7AmFWiSyM8rG_+7C=wTqiP0oCa9QAPe0Y0_wH=Q@mail.gmail.com>
Date:   Thu, 4 Jun 2020 02:08:59 +0530
From:   Bhupesh Sharma <bhsharma@...hat.com>
To:     Scott Branden <scott.branden@...adcom.com>
Cc:     James Morse <james.morse@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Will Deacon <will@...nel.org>, x86@...nel.org,
        kexec mailing list <kexec@...ts.infradead.org>,
        Kazuhito Hagio <k-hagio@...jp.nec.com>,
        Dave Anderson <anderson@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Bhupesh SHARMA <bhupesh.linux@...il.com>,
        linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Steve Capper <steve.capper@....com>
Subject: Re: Re: [RESEND PATCH v5 5/5] Documentation/vmcoreinfo: Add
 documentation for 'TCR_EL1.T1SZ'

Hello Scott,

On Thu, Jun 4, 2020 at 12:17 AM Scott Branden
<scott.branden@...adcom.com> wrote:
>
> Hi Bhupesh,
>
> Would be great to get this patch series upstreamed?
>
> On 2019-12-25 10:49 a.m., Bhupesh Sharma wrote:
> > Hi James,
> >
> > On 12/12/2019 04:02 PM, James Morse wrote:
> >> Hi Bhupesh,
> >
> > I am sorry this review mail skipped my attention due to holidays and
> > focus on other urgent issues.
> >
> >> On 29/11/2019 19:59, Bhupesh Sharma wrote:
> >>> Add documentation for TCR_EL1.T1SZ variable being added to
> >>> vmcoreinfo.
> >>>
> >>> It indicates the size offset of the memory region addressed by
> >>> TTBR1_EL1
> >>
> >>> and hence can be used for determining the vabits_actual value.
> >>
> >> used for determining random-internal-kernel-variable, that might not
> >> exist tomorrow.
> >>
> >> Could you describe how this is useful/necessary if a debugger wants
> >> to walk the page
> >> tables from the core file? I think this is a better argument.
> >>
> >> Wouldn't the documentation be better as part of the patch that adds
> >> the export?
> >> (... unless these have to go via different trees? ..)
> >
> > Ok, will fix the same in v6 version.
> >
> >>> diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst
> >>> b/Documentation/admin-guide/kdump/vmcoreinfo.rst
> >>> index 447b64314f56..f9349f9d3345 100644
> >>> --- a/Documentation/admin-guide/kdump/vmcoreinfo.rst
> >>> +++ b/Documentation/admin-guide/kdump/vmcoreinfo.rst
> >>> @@ -398,6 +398,12 @@ KERNELOFFSET
> >>>   The kernel randomization offset. Used to compute the page offset. If
> >>>   KASLR is disabled, this value is zero.
> >>>   +TCR_EL1.T1SZ
> >>> +------------
> >>> +
> >>> +Indicates the size offset of the memory region addressed by TTBR1_EL1
> >>
> >>> +and hence can be used for determining the vabits_actual value.
> >>
> >> 'vabits_actual' may not exist when the next person comes to read this
> >> documentation (its
> >> going to rot really quickly).
> >>
> >> I think the first half of this text is enough to say what this is
> >> for. You should include
> >> words to the effect that its the hardware value that goes with
> >> swapper_pg_dir. You may
> >> want to point readers to the arm-arm for more details on what the
> >> value means.
> >
> > Ok, got it. Fixed this in v6, which should be on its way shortly.
> I can't seem to find v6?

Oops. I remember Cc'ing you to the v6 patchset (may be my email client
messed up), anyways here is the v6 patchset for your reference:
<http://lists.infradead.org/pipermail/kexec/2020-May/025095.html>

Do share your review/test comments on the same.

Thanks,
Bhupesh