linux-kernel - Re: [Patch v3 Part2 1/9] x86/microcode: Taint kernel only if microcode loading was successful

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Message-ID: <Y9l4FdvytLqMc3jm@zn.tnic>
Date:   Tue, 31 Jan 2023 21:20:37 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Ashok Raj <ashok.raj@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Stefan Talpalaru <stefantalpalaru@...oo.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Jonathan Corbet <corbet@....net>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Peter Zilstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Martin Pohlack <mpohlack@...zon.de>,
        "Li, Aubrey" <aubrey.li@...el.com>
Subject: Re: [Patch v3 Part2 1/9] x86/microcode: Taint kernel only if
 microcode loading was successful

On Tue, Jan 31, 2023 at 08:51:25AM -0800, Ashok Raj wrote:
> remove ret = 0 during initialization since its cleared right below. (tglx)

Sure.

> Need to set ret explicitly to either -EINVAL, or size. Otherwise it will be
> endlessly waiting for write to complete. (As Aubrey pointed out)

Then do:

        tmp_ret = microcode_ops->request_microcode_fw(bsp, &microcode_pdev->dev);
        if (tmp_ret != UCODE_NEW)
                return size;

to signal what it is. It certainly ain't an error if it doesn't find new
microcode.

> I think its safe to leave ret as is, since microcode_reload_late() only
> returns -1, or 0.

No it doesn't. Hint: stop_machine_cpuslocked().

> Pull this into the ret == 0, so taint only if the update was successful? 

Ok.

> And add a message so its not silent?

You'd add a printk for every possible operation, wouldn't you?

See, the world doesn't revolve around microcode loading. If that thing
fails, then someone has done a bad job at the CPU vendor testing,
provided the code does the right thing.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette