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From: Thomas Gleixner <tglx@linutronix.de>
To: Laura Nao <laura.nao@collabora.com>
Cc: kernel@collabora.com, laura.nao@collabora.com,
 linux-kernel@vger.kernel.org, regressions@leemhuis.info,
 regressions@lists.linux.dev, x86@kernel.org
Subject: Re: [REGRESSION] mainline boot regression on AMD Stoney Ridge
 Chromebooks
In-Reply-To: <87sf019kbd.ffs@tglx>
References: <874jchb7na.ffs@tglx>
 <20240404152317.464796-1-laura.nao@collabora.com> <87sf019kbd.ffs@tglx>
Date: Thu, 04 Apr 2024 20:06:50 +0200
Message-ID: <87plv59f45.ffs@tglx>
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Laura!

On Thu, Apr 04 2024 at 18:14, Thomas Gleixner wrote:
> Can you please provide 'cpuid -r' output too as 'cpuid' does a few
> tweaks to the raw data and it's hard to match it back to the code.

Don't bother. I think I figured it out.

Can you please test the patch below?

Thanks,

        tglx
---
diff --git a/arch/x86/kernel/cpu/topology_amd.c b/arch/x86/kernel/cpu/topology_amd.c
index 1a8b3ad493af..0d91a04b1741 100644
--- a/arch/x86/kernel/cpu/topology_amd.c
+++ b/arch/x86/kernel/cpu/topology_amd.c
@@ -29,7 +29,17 @@ static bool parse_8000_0008(struct topo_scan *tscan)
 	if (!sft)
 		sft = get_count_order(ecx.cpu_nthreads + 1);
 
-	topology_set_dom(tscan, TOPO_SMT_DOMAIN, sft, ecx.cpu_nthreads + 1);
+	/*
+	 * cpu_nthreads describes the number of threads in the package
+	 * sft is the number of APIC ID bits per package
+	 *
+	 * As the number of actual threads per core is not described in
+	 * this leaf, just set the CORE domain shift and let the later
+	 * parsers set SMT shift. Assume one thread per core by default
+	 * which is correct if there are no other CPUID leafs to parse.
+	 */
+	topology_update_dom(tscan, TOPO_SMT_DOMAIN, 0, 1);
+	topology_set_dom(tscan, TOPO_CORE_DOMAIN, sft, ecx.cpu_nthreads + 1);
 	return true;
 }
 
@@ -73,12 +83,14 @@ static bool parse_8000_001e(struct topo_scan *tscan, bool has_0xb)
 	tscan->c->topo.initial_apicid = leaf.ext_apic_id;
 
 	/*
-	 * If leaf 0xb is available, then SMT shift is set already. If not
-	 * take it from ecx.threads_per_core and use topo_update_dom() -
-	 * topology_set_dom() would propagate and overwrite the already
-	 * propagated CORE level.
+	 * If leaf 0xb is available, then the domain shifts are set
+	 * already and nothing to do here.
 	 */
 	if (!has_0xb) {
+		/*
+		 * Leaf 0x80000008 set the CORE domain shift already.
+		 * Update the SMT domain, but do not propagate it.
+		 */
 		unsigned int nthreads = leaf.core_nthreads + 1;
 
 		topology_update_dom(tscan, TOPO_SMT_DOMAIN, get_count_order(nthreads), nthreads);