linux-kernel - [v2 03/13] x86/microcode/intel: Fix a hang if early loading microcode fails

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Date:   Thu,  3 Nov 2022 17:58:51 +0000
From:   Ashok Raj <ashok.raj@...el.com>
To:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     "LKML Mailing List" <linux-kernel@...r.kernel.org>,
        X86-kernel <x86@...nel.org>, Tony Luck <tony.luck@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Arjan van de Ven <arjan.van.de.ven@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Jacon Jun Pan <jacob.jun.pan@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Kai Huang <kai.huang@...el.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Ashok Raj <ashok.raj@...el.com>
Subject: [v2 03/13] x86/microcode/intel: Fix a hang if early loading microcode fails

When early loading of microcode fails for any reason other than the wrong
family-model-stepping, Linux can get into an infinite loop retrying the
same failed load.

A single retry is needed to handle any mixed stepping case.

Assume we have a microcode that fails to load for some reason.
load_ucode_ap() seems to retry if the loading fails. But it searches for
a new rev, but ends up finding the same copy. Hence it appears to repeat
the same load, retry loop for ever.

load_ucode_intel_ap()
{
..
reget:
        if (!*iup) {
                patch = __load_ucode_intel(&uci);
		^^^^^ Finds the same patch every time.

                if (!patch)
                        return;

                *iup = patch;
        }

        uci.mc = *iup;

        if (apply_microcode_early(&uci, true)) {
	^^^^^^^^^^^^ apply fails
              /* Mixed-silicon system? Try to refetch the proper patch: */
              *iup = NULL;

              goto reget;
	      ^^^^^ Rince repeat.
        }

}

Fixes: 06b8534cb728 ("x86/microcode: Rework microcode loading")
Reviewed-by: Tony Luck <tony.luck@...el.com>
Signed-off-by: Ashok Raj <ashok.raj@...el.com>
---
 arch/x86/kernel/cpu/microcode/intel.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 733b5eac0444..8ef04447fcf0 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -606,6 +606,7 @@ void __init load_ucode_intel_bsp(void)
 {
 	struct microcode_intel *patch;
 	struct ucode_cpu_info uci;
+	int rev, ret;
 
 	patch = __load_ucode_intel(&uci);
 	if (!patch)
@@ -613,13 +614,18 @@ void __init load_ucode_intel_bsp(void)
 
 	uci.mc = patch;
 
-	apply_microcode_early(&uci, true);
+	ret = apply_microcode_early(&uci, true);
+	if (ret) {
+		rev = patch->hdr.rev;
+		pr_err("Revision 0x%x failed during early loading\n", rev);
+	}
 }
 
 void load_ucode_intel_ap(void)
 {
 	struct microcode_intel *patch, **iup;
 	struct ucode_cpu_info uci;
+	bool retried = false;
 
 	if (IS_ENABLED(CONFIG_X86_32))
 		iup = (struct microcode_intel **) __pa_nodebug(&intel_ucode_patch);
@@ -638,9 +644,13 @@ void load_ucode_intel_ap(void)
 	uci.mc = *iup;
 
 	if (apply_microcode_early(&uci, true)) {
+		if (retried)
+			return;
+
 		/* Mixed-silicon system? Try to refetch the proper patch: */
 		*iup = NULL;
 
+		retried = true;
 		goto reget;
 	}
 }
-- 
2.34.1