linux-kernel - [PATCH v4 04/16] x86/pvh: Use fixed_percpu

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Date: Fri, 22 Mar 2024 12:52:21 -0400
From: Brian Gerst <brgerst@...il.com>
To: linux-kernel@...r.kernel.org,
	x86@...nel.org
Cc: Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	"H . Peter Anvin" <hpa@...or.com>,
	Uros Bizjak <ubizjak@...il.com>,
	David.Laight@...lab.com,
	Brian Gerst <brgerst@...il.com>
Subject: [PATCH v4 04/16] x86/pvh: Use fixed_percpu_data for early boot GSBASE

Instead of having a private area for the stack canary, use
fixed_percpu_data for GSBASE like the native kernel.

Signed-off-by: Brian Gerst <brgerst@...il.com>
---
 arch/x86/platform/pvh/head.S | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S
index f7235ef87bc3..1f1c3230b27b 100644
--- a/arch/x86/platform/pvh/head.S
+++ b/arch/x86/platform/pvh/head.S
@@ -95,10 +95,15 @@ SYM_CODE_START_LOCAL(pvh_start_xen)
 	/* 64-bit entry point. */
 	.code64
 1:
-	/* Set base address in stack canary descriptor. */
+	/*
+	 * Set up GSBASE.
+	 * Note that, on SMP, the boot cpu uses init data section until
+	 * the per cpu areas are set up.
+	 */
 	mov $MSR_GS_BASE,%ecx
-	mov $_pa(canary), %eax
-	xor %edx, %edx
+	lea INIT_PER_CPU_VAR(fixed_percpu_data)(%rip), %rdx
+	mov %edx, %eax
+	shr $32, %rdx
 	wrmsr
 
 	call xen_prepare_pvh
@@ -157,8 +162,6 @@ SYM_DATA_START_LOCAL(gdt_start)
 SYM_DATA_END_LABEL(gdt_start, SYM_L_LOCAL, gdt_end)
 
 	.balign 16
-SYM_DATA_LOCAL(canary, .fill 48, 1, 0)
-
 SYM_DATA_START_LOCAL(early_stack)
 	.fill BOOT_STACK_SIZE, 1, 0
 SYM_DATA_END_LABEL(early_stack, SYM_L_LOCAL, early_stack_end)
-- 
2.44.0