linux-kernel - Re: [PATCH v2 12/14] platform/x86/intel/ifs: Add current

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Date:   Sun, 13 Nov 2022 13:33:50 -0800
From:   Tony Luck <tony.luck@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Joseph, Jithu" <jithu.joseph@...el.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Thiago Macieira <thiago.macieira@...el.com>,
        "hdegoede@...hat.com" <hdegoede@...hat.com>,
        "markgross@...nel.org" <markgross@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "Jimenez Gonzalez, Athenas" <athenas.jimenez.gonzalez@...el.com>,
        "Mehta, Sohil" <sohil.mehta@...el.com>
Subject: Re: [PATCH v2 12/14] platform/x86/intel/ifs: Add current_batch sysfs
 entry

On Sun, Nov 13, 2022 at 07:27:26PM +0100, Borislav Petkov wrote:
> On Sun, Nov 13, 2022 at 09:55:00AM -0800, Joseph, Jithu wrote:
> > Then we were told not to specify a filename via sysfs file (apologies
> > for being repetitive)
> 
> Yeah, I'm unclear on why that is either and am hoping that Greg will
> clarify. He fears that there will be file path resolution which I'm not
> even thinking about.

Summarizing the competing proposals here:

Option 1 (patches as currently posted)

	User writes the batch number to the sysfs file:

	# echo 4 > /sys/devices/virtual/misc/intel_ifs_0/current_batch

	Driver turns that into a *partial* path (with test type, family-model-stepping
	and batch number filled in):

		"intel/ifs_%d/%02x-%02x-%02x-%02x.scan"

	Feeds that to request_firmware_direct() (which looks in /lib/firmware)

Option 2 (proposed by Boris)

	User writes a filename to the sysfs file:

	# echo 06-8f-06-04.scan > /sys/devices/virtual/misc/intel_ifs_0/current_batch

	Driver parses that:
		If family-mode-stepping does not match current CPU, then
		fail with -EINVAL
		If filename doesn't end with a ".scan" suffix, also
		fails with -EINVAL

	Otherwise proceeds in similar manner to above. Constructs partial
	pathname (just fills in test type and filename:

		"intel/ifs_%d/%s"

	Feeds that to request_firmware_direct() (which looks in /lib/firmware)


IMHO option 1 is following the microcode precedent of having the kernel
construct the filename based on the {x86,model,stepping} fields of
struct cpuinfo_x86.

I think option 2 isn't really doing the user any favors. Having them
feed all the *.scan files they find in /lib/firmware/intel/ifs_0 to the
driver to see which ones work becomes progressively worse in every CPU
generation. Any script/app running tests is likely to do the ff-mm-ss
filter itself ... so why have the kernel do it too?

-Tony