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SubjectRe: [PATCH v9 0/8] Parallel CPU bringup for x86_64
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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? :)

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@amazon.co.uk>
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 */
--
2.39.0

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