From:   Brian Gerst <brgerst@gmail.com>
To:     linux-kernel@vger.kernel.org, x86@kernel.org
Cc:     David Woodhouse <dwmw2@infradead.org>,
        Usama Arif <usama.arif@bytedance.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Brian Gerst <brgerst@gmail.com>,
        David Woodhouse <dwmw@amazon.co.uk>
Subject: [PATCH v2 1/5] x86/smpboot: Remove initial_stack on 64-bit
Date:   Fri, 24 Feb 2023 10:42:31 -0500
Message-Id: <20230224154235.277350-2-brgerst@gmail.com>
In-Reply-To: <20230224154235.277350-1-brgerst@gmail.com>
References: <20230224154235.277350-1-brgerst@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Load RSP from current_task->thread.sp instead.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Tested-by: Usama Arif <usama.arif@bytedance.com>
Signed-off-by: Usama Arif <usama.arif@bytedance.com>
---
 arch/x86/include/asm/processor.h |  6 +++++-
 arch/x86/kernel/acpi/sleep.c     |  2 +-
 arch/x86/kernel/head_64.S        | 35 ++++++++++++++++++--------------
 arch/x86/xen/xen-head.S          |  2 +-
 4 files changed, 27 insertions(+), 18 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 8d73004e4cac..a1e4fa58b357 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -647,7 +647,11 @@ static inline void spin_lock_prefetch(const void *x)
 #define KSTK_ESP(task)		(task_pt_regs(task)->sp)
 
 #else
-#define INIT_THREAD { }
+extern unsigned long __end_init_task[];
+
+#define INIT_THREAD {							    \
+	.sp	= (unsigned long)&__end_init_task - sizeof(struct pt_regs), \
+}
 
 extern unsigned long KSTK_ESP(struct task_struct *task);
 
diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
index 47e75c056cb5..008fda8b1982 100644
--- a/arch/x86/kernel/acpi/sleep.c
+++ b/arch/x86/kernel/acpi/sleep.c
@@ -113,7 +113,7 @@ int x86_acpi_suspend_lowlevel(void)
 	saved_magic = 0x12345678;
 #else /* CONFIG_64BIT */
 #ifdef CONFIG_SMP
-	initial_stack = (unsigned long)temp_stack + sizeof(temp_stack);
+	current->thread.sp = (unsigned long)temp_stack + sizeof(temp_stack);
 	early_gdt_descr.address =
 			(unsigned long)get_cpu_gdt_rw(smp_processor_id());
 	initial_gs = per_cpu_offset(smp_processor_id());
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index c32e5b06a9ce..f7905ba4b992 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -62,8 +62,8 @@ SYM_CODE_START_NOALIGN(startup_64)
 	 * tables and then reload them.
 	 */
 
-	/* Set up the stack for verify_cpu(), similar to initial_stack below */
-	leaq	(__end_init_task - FRAME_SIZE)(%rip), %rsp
+	/* Set up the stack for verify_cpu() */
+	leaq	(__end_init_task - PTREGS_SIZE)(%rip), %rsp
 
 	leaq	_text(%rip), %rdi
 
@@ -245,11 +245,11 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
 #ifdef CONFIG_SMP
 	/*
 	 * Is this the boot CPU coming up? If so everything is available
-	 * in initial_gs, initial_stack and early_gdt_descr.
+	 * in initial_gs and early_gdt_descr.
 	 */
 	movl	smpboot_control(%rip), %edx
 	testl	$STARTUP_SECONDARY, %edx
-	jz	.Lsetup_cpu
+	jz	.Linit_cpu0_data
 
 	/*
 	 * For parallel boot, the APIC ID is retrieved from CPUID, and then
@@ -302,6 +302,10 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
 	hlt
 	jmp	1b
 
+.Linit_cpu0_data:
+	movq	__per_cpu_offset(%rip), %rdx
+	jmp	.Lsetup_cpu
+
 .Linit_cpu_data:
 	/* Get the per cpu offset for the given CPU# which is in ECX */
 	leaq	__per_cpu_offset(%rip), %rbx
@@ -314,13 +318,21 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
 	addq	%rbx, %rcx
 	movq	%rcx, early_gdt_descr_base(%rip)
 
-	/* Find the idle task stack */
-	movq	pcpu_hot + X86_current_task(%rbx), %rcx
-	movq	TASK_threadsp(%rcx), %rcx
-	movq	%rcx, initial_stack(%rip)
+	movq	%rbx, %rdx
+#else
+	xorl	%edx, %edx
 #endif /* CONFIG_SMP */
 
 .Lsetup_cpu:
+	/*
+	 * Setup a boot time stack - Any secondary CPU will have lost its stack
+	 * by now because the cr3-switch above unmaps the real-mode stack
+	 *
+	 * RDX contains the per-cpu offset
+	 */
+	movq	pcpu_hot + X86_current_task(%rdx), %rax
+	movq	TASK_threadsp(%rax), %rsp
+
 	/*
 	 * We must switch to a new descriptor in kernel space for the GDT
 	 * because soon the kernel won't have access anymore to the userspace
@@ -355,12 +367,6 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
 	movl	initial_gs+4(%rip),%edx
 	wrmsr
 
-	/*
-	 * Setup a boot time stack - Any secondary CPU will have lost its stack
-	 * by now because the cr3-switch above unmaps the real-mode stack
-	 */
-	movq initial_stack(%rip), %rsp
-
 	/* Drop the realmode protection. For the boot CPU the pointer is NULL! */
 	movq	trampoline_lock(%rip), %rax
 	testq	%rax, %rax
@@ -517,7 +523,6 @@ SYM_DATA(initial_vc_handler,	.quad handle_vc_boot_ghcb)
  * The FRAME_SIZE gap is a convention which helps the in-kernel unwinder
  * reliably detect the end of the stack.
  */
-SYM_DATA(initial_stack, .quad init_thread_union + THREAD_SIZE - FRAME_SIZE)
 SYM_DATA(trampoline_lock, .quad 0);
 	__FINITDATA
 
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index e36ea4268bd2..91f7a53519a7 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -49,7 +49,7 @@ SYM_CODE_START(startup_xen)
 	ANNOTATE_NOENDBR
 	cld
 
-	mov initial_stack(%rip), %rsp
+	leaq	(__end_init_task - PTREGS_SIZE)(%rip), %rsp
 
 	/* Set up %gs.
 	 *
-- 
2.39.2