linux-kernel - Re: [PATCH v2] tools/power turbostat: Fix RAPL summary collection on AMD processors

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Message-ID: <23f75aaf3d37cbad6f8ed7bd970434e4a2dc388e.camel@kepstin.ca>
Date:   Fri, 23 Apr 2021 10:00:14 -0400
From:   Calvin Walton <calvin.walton@...stin.ca>
To:     Borislav Petkov <bp@...e.de>, Chen Yu <yu.c.chen@...el.com>
Cc:     Terry Bowman <terry.bowman@....com>, lenb@...nel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        wei.huang2@....com, aros@....com, rui.zhang@...el.com
Subject: Re: [PATCH v2] tools/power turbostat: Fix RAPL summary collection
 on AMD processors

On Fri, 2021-04-23 at 14:19 +0200, Borislav Petkov wrote:
> On Fri, Apr 23, 2021 at 08:16:07PM +0800, Chen Yu wrote:
> > From b2e63fe4f02e17289414b4f61237da822df115fb Mon Sep 17 00:00:00
> > 2001
> > From: Calvin Walton <calvin.walton@...stin.ca>
> > Date: Fri, 23 Apr 2021 17:32:13 +0800
> > Subject: [PATCH 3/5] tools/power turbostat: Fix offset overflow
> > issue in index
> >  converting
> > 
> > The idx_to_offset() function returns type int (32-bit signed), but
> > MSR_PKG_ENERGY_STAT is greater than INT_MAX (or rather, would be
> > interpreted as a negative number). The end result is that it hits
> > the if (offset < 0) check in update_msr_sum() resulting in the
> > timer
> > callback for updating the stat in the background when long
> > durations
> > are used to not happen. The similar issue exists in offset_to_idx()
> > and update_msr_sum().
> > 
> > This patch fixes this issue by converting the 'int' type to 'off_t'
> > accordingly.
> > 
> > Fixes: 9972d5d84d76 ("tools/power turbostat: Enable accumulate RAPL
> > display")
> > Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> 
> This patch's authorship is weird: it says From: Calvin but doesn't
> have
> his SOB here - only yours.

I think this patch is adapted from one of my earlier submissions? I
don't think I can really say that I wrote it, but I'll certainly review
it.

> 
> > ---
> >  tools/power/x86/turbostat/turbostat.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/tools/power/x86/turbostat/turbostat.c
> > b/tools/power/x86/turbostat/turbostat.c
> > index a211264b57fd..77557122b292 100644
> > --- a/tools/power/x86/turbostat/turbostat.c
> > +++ b/tools/power/x86/turbostat/turbostat.c
> > @@ -296,9 +296,9 @@ struct msr_sum_array {
> >  /* The percpu MSR sum array.*/
> >  struct msr_sum_array *per_cpu_msr_sum;
> >  
> > -int idx_to_offset(int idx)
> > +off_t idx_to_offset(int idx)
> 
> And this is silly. MSRs are unsigned int. Fullstop.
> 
> So that function should either return u32 or unsigned int or so.

So, there's two problems with that:
   1. This function needs to be able to return an error value that cannot be
      confused with a valid MSR. This is currently done by returning a
      negative number. If an unsigned value is used, a different way of
      indicating errors needs to be written.
   2. We are not using CPU instructions to access MSRs direction. Instead
      they are being read from /dev/msr. So the "offset" value is actually a
      seek into the /dev/msr file (using pread), and thus is of type off_t.

-- 
Calvin Walton <calvin.walton@...stin.ca>