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

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Date:   Tue, 31 Jan 2023 12:50:44 +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>
Subject: Re: [Patch v3 Part2 1/9] x86/microcode: Taint kernel only if
 microcode loading was successful

On Mon, Jan 30, 2023 at 01:39:47PM -0800, Ashok Raj wrote:
>  arch/x86/kernel/cpu/microcode/core.c | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)

Why all this hoopla and unrelated changes?

Why don't you simply hoist the call to ->request_microcode_fw outside of
the locked region as it doesn't have to be there and then do the usual
pattern?

---
diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 14a2280fdcd2..23f4f22df581 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -481,28 +481,28 @@ static ssize_t reload_store(struct device *dev,
 	if (val != 1)
 		return size;
 
+	tmp_ret = microcode_ops->request_microcode_fw(bsp, &microcode_pdev->dev);
+	if (tmp_ret != UCODE_NEW)
+		return ret;
+
 	cpus_read_lock();
 
 	ret = check_online_cpus();
 	if (ret)
-		goto put;
-
-	tmp_ret = microcode_ops->request_microcode_fw(bsp, &microcode_pdev->dev);
-	if (tmp_ret != UCODE_NEW)
-		goto put;
+		goto unlock;
 
 	mutex_lock(&microcode_mutex);
 	ret = microcode_reload_late();
 	mutex_unlock(&microcode_mutex);
 
-put:
-	cpus_read_unlock();
-
 	if (ret == 0)
 		ret = size;
 
 	add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
 
+unlock:
+	cpus_read_unlock();
+
 	return ret;
 }
 

-- 
Regards/Gruss,
    Boris.

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