linux-kernel - Re: [PATCH v1 2/2] firmware: dmi_scan: Pass dmi_entry

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Message-ID: <20200121172403.GA32742@smile.fi.intel.com>
Date:   Tue, 21 Jan 2020 19:24:03 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Jean Delvare <jdelvare@...e.de>, Dave Young <dyoung@...hat.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        kexec@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH v1 2/2] firmware: dmi_scan: Pass dmi_entry_point to
 kexec'ed kernel

On Tue, Jan 21, 2020 at 10:29:35AM -0600, Eric W. Biederman wrote:
> Jean Delvare <jdelvare@...e.de> writes:
> 
> > On Mon, 20 Jan 2020 23:55:43 +0200, Andy Shevchenko wrote:
> >> On Mon, Jan 20, 2020 at 11:44 PM Jean Delvare <jdelvare@...e.de> wrote:
> >> >
> >> > On Mon, 20 Jan 2020 10:04:04 -0600, Eric W. Biederman wrote:  
> >> > > Second.  I looked at your test results and they don't directly make
> >> > > sense.  dmidecode bypasses the kernel completely or it did last time
> >> > > I looked so I don't know why you would be using that to test if
> >> > > something in the kernel is working.  
> >> >
> >> > That must have been long ago. A recent version of dmidecode (>= 3.0)
> >> > running on a recent kernel  
> >> > (>= d7f96f97c4031fa4ffdb7801f9aae23e96170a6f, v4.2) will read the DMI  
> >> > data from /sys/firmware/dmi/tables, so it is very much relying on the
> >> > kernel doing the right thing. If not, it will still try to fallback to
> >> > reading from /dev/mem directly on certain architectures. You can force
> >> > that old method with --no-sysfs.
> >> >
> >> > Hope that helps,  
> >> 
> >> I don't understand how it possible can help for in-kernel code, like
> >> DMI quirks in a drivers.
> >
> > OK, just ignore me then, probably I misunderstood the point made by
> > Eric.
> 
> No.  I just haven't dived into this area of code in a long time.
> 
> It seems a little indirect to use dmidecode as the test to see if the
> kernel has the pointer to the dmitables, but with the knowledge you
> provided it seems like a perfectly valid test.

In any case that doesn't work. See my response to Ard.

-- 
With Best Regards,
Andy Shevchenko