Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64

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On 21.02.2023 09:17, David Woodhouse wrote:
On Tue, 2023-02-21 at 09:05 +0100, Oleksandr Natalenko wrote:

Please see here: http://ix.io/4oLm

Was that just for one CPU? Can we have them all please?

The interesting part is the line starting 00000001. We're looking at
the top 8 bits of EBX:

Leaf     Subleaf    EAX            EBX            ECX            EDX
00000000 00000000: 00000010 .... 68747541 Auth 444d4163 cAMD 69746e65 enti 00000001 00000000: 00a20f12 .... 00200800 .. . 7ef8320b .2.~ 178bfbff ....
                                   ↑↑

So the first CPU is CPU0. Could have told you that... what about the others? :)

Right, sorry. Here it is: http://ix.io/4oLq

If anyone can reproduce this with a serial port, can you try this?

From 98ad11d0fb88f081f49f7b1496420dbfbeff8833 Mon Sep 17 00:00:00 2001
From: David Woodhouse <dwmw@xxxxxxxxxxxx>
Date: Sat, 4 Feb 2023 15:20:24 +0000
Subject: [PATCH] parallel debug

---
 arch/x86/kernel/head_64.S | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 0e4e53d231db..da7f4d2d9951 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -281,6 +281,15 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)

 .Lsetup_AP:
 	/* EDX contains the APIC ID of the current CPU */
+#if 1
+	/* Test hack: Print APIC ID and then CPU# when we find it. */
+	mov	%edx, %ecx
+	mov	%edx, %eax
+	addb	$'A', %al
+	mov	$0x3f8, %dx
+	outb    %al, %dx
+	mov	%ecx, %edx
+#endif
 	xorq	%rcx, %rcx
 	leaq	cpuid_to_apicid(%rip), %rbx

@@ -302,6 +311,14 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)

 .Linit_cpu_data:
 	/* Get the per cpu offset for the given CPU# which is in ECX */
+#if 1
+	mov	%rcx, %rax
+	shr	$3, %rax
+	addb	$'a', %al
+
+	mov	$0x3f8, %dx
+	outb    %al, %dx
+#endif
 	leaq	__per_cpu_offset(%rip), %rbx
 	movq	(%rbx,%rcx,8), %rbx
 	/* Save it for GS BASE setup */

--
  Oleksandr Natalenko (post-factum)



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