[Patch v3 Part2 4/9] x86/microcode: Do not call apply_microcode() on sibling threads

[Ashok Raj]

Microcode updates are applied at the core, so an update to one HT sibling
is effective on all HT siblings of the same core.

During late-load, after the primary has updated the microcode, it also
reflects that in the per-cpu structure (cpuinfo_x86) holding the current
revision.

Current code calls apply_microcode() to update the SW per-cpu revision.

But in the odd case when primary returned with an error, and as a result
the secondary didn't get the revision updated, will attempt to perform
a patch load and the primary has already been released to the system.
This could be problematic, because the whole rendezvous dance is to
prevent updates when one of the siblings could be executing arbitrary code.

Replace apply_microcode() with a call to collect_cpu_info() and let that
call also update the per-cpu structure instead of returning the previously
cached values.

Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
Cc: LKML <linux-kernel@xxxxxxxxxxxxxxx>
Cc: x86 <x86@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Alison Schofield <alison.schofield@xxxxxxxxx>
Cc: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Cc: Thomas Gleixner (Intel) <tglx@xxxxxxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Stefan Talpalaru <stefantalpalaru@xxxxxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Rafael J. Wysocki <rafael@xxxxxxxxxx>
Cc: Peter Zilstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Martin Pohlack <mpohlack@xxxxxxxxx>
---
 arch/x86/kernel/cpu/microcode/core.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index e4b4dfcf2d18..8452fad89bf6 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -386,6 +386,7 @@ static int __wait_for_cpus(atomic_t *t, long long timeout)
 static int __reload_late(void *info)
 {
 	int cpu = smp_processor_id();
+	struct ucode_cpu_info *uci;
 	enum ucode_state err;
 	int ret = 0;
 
@@ -421,12 +422,13 @@ static int __reload_late(void *info)
 
 	/*
 	 * At least one thread has completed update on each core.
-	 * For others, simply call the update to make sure the
-	 * per-cpu cpuinfo can be updated with right microcode
-	 * revision.
+	 * For siblings, collect the cpuinfo and update the
+	 * per-cpu cpuinfo with the current microcode revision.
 	 */
-	if (cpumask_first(topology_sibling_cpumask(cpu)) != cpu)
-		err = microcode_ops->apply_microcode(cpu);
+	if (cpumask_first(topology_sibling_cpumask(cpu)) != cpu) {
+		uci = ucode_cpu_info + cpu;
+		microcode_ops->collect_cpu_info(cpu, &uci->cpu_sig);
+	}
 
 	return ret;
 }
-- 
2.37.2