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 3/5] x86/smpboot: Remove initial_gs
Date:   Fri, 24 Feb 2023 10:42:33 -0500
Message-Id: <20230224154235.277350-4-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

Use the percpu offset directly to set GSBASE.

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/realmode.h |  1 -
 arch/x86/kernel/acpi/sleep.c    |  1 -
 arch/x86/kernel/head_64.S       | 34 ++++++++++-----------------------
 3 files changed, 10 insertions(+), 26 deletions(-)

diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
index f0357cfe2fb0..87e5482acd0d 100644
--- a/arch/x86/include/asm/realmode.h
+++ b/arch/x86/include/asm/realmode.h
@@ -60,7 +60,6 @@ extern struct real_mode_header *real_mode_header;
 extern unsigned char real_mode_blob_end[];
 
 extern unsigned long initial_code;
-extern unsigned long initial_gs;
 extern unsigned long initial_stack;
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 extern unsigned long initial_vc_handler;
diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
index 6538ddb55f28..214dd4a79860 100644
--- a/arch/x86/kernel/acpi/sleep.c
+++ b/arch/x86/kernel/acpi/sleep.c
@@ -114,7 +114,6 @@ int x86_acpi_suspend_lowlevel(void)
 #else /* CONFIG_64BIT */
 #ifdef CONFIG_SMP
 	current->thread.sp = (unsigned long)temp_stack + sizeof(temp_stack);
-	initial_gs = per_cpu_offset(smp_processor_id());
 	/* Force the startup into boot mode */
 	saved_smpboot_ctrl = xchg(&smpboot_control, 0);
 #endif
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 0dd57d573a0e..9ed87ba0609f 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -67,18 +67,10 @@ SYM_CODE_START_NOALIGN(startup_64)
 
 	leaq	_text(%rip), %rdi
 
-	/*
-	 * initial_gs points to initial fixed_percpu_data struct with storage for
-	 * the stack protector canary. Global pointer fixups are needed at this
-	 * stage, so apply them as is done in fixup_pointer(), and initialize %gs
-	 * such that the canary can be accessed at %gs:40 for subsequent C calls.
-	 */
+	/* Setup GSBASE to allow stack canary access for C code */
 	movl	$MSR_GS_BASE, %ecx
-	movq	initial_gs(%rip), %rax
-	movq	$_text, %rdx
-	subq	%rdx, %rax
-	addq	%rdi, %rax
-	movq	%rax, %rdx
+	leaq	INIT_PER_CPU_VAR(fixed_percpu_data)(%rip), %rdx
+	movl	%edx, %eax
 	shrq	$32,  %rdx
 	wrmsr
 
@@ -243,10 +235,7 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
 	ANNOTATE_NOENDBR // above
 
 #ifdef CONFIG_SMP
-	/*
-	 * Is this the boot CPU coming up? If so everything is available
-	 * in initial_gs.
-	 */
+	/* Is this the boot CPU coming up? */
 	movl	smpboot_control(%rip), %edx
 	testl	$STARTUP_SECONDARY, %edx
 	jz	.Linit_cpu0_data
@@ -308,12 +297,7 @@ 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 */
-	leaq	__per_cpu_offset(%rip), %rbx
-	movq	(%rbx,%rcx,8), %rbx
-	/* Save it for GS BASE setup */
-	movq	%rbx, initial_gs(%rip)
-
-	movq	%rbx, %rdx
+	movq	__per_cpu_offset(,%rcx,8), %rdx
 #else
 	xorl	%edx, %edx
 #endif /* CONFIG_SMP */
@@ -363,8 +347,11 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
 	 * the per cpu areas are set up.
 	 */
 	movl	$MSR_GS_BASE,%ecx
-	movl	initial_gs(%rip),%eax
-	movl	initial_gs+4(%rip),%edx
+#ifndef CONFIG_SMP
+	leaq	INIT_PER_CPU_VAR(fixed_percpu_data)(%rip), %rdx
+#endif
+	movl	%edx, %eax
+	shrq	$32, %rdx
 	wrmsr
 
 	/* Drop the realmode protection. For the boot CPU the pointer is NULL! */
@@ -514,7 +501,6 @@ SYM_CODE_END(vc_boot_ghcb)
 	__REFDATA
 	.balign	8
 SYM_DATA(initial_code,	.quad x86_64_start_kernel)
-SYM_DATA(initial_gs,	.quad INIT_PER_CPU_VAR(fixed_percpu_data))
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 SYM_DATA(initial_vc_handler,	.quad handle_vc_boot_ghcb)
 #endif
-- 
2.39.2