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From:   Brian Gerst <brgerst@gmail.com>
To:     linux-kernel@vger.kernel.org, x86@kernel.org
Cc:     Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Uros Bizjak <ubizjak@gmail.com>, David.Laight@aculab.com,
        Brian Gerst <brgerst@gmail.com>
Subject: [PATCH v3 04/14] x86/pvh: Use fixed_percpu_data for early boot GSBASE
Date:   Wed, 15 Nov 2023 12:36:58 -0500
Message-ID: <20231115173708.108316-5-brgerst@gmail.com>
In-Reply-To: <20231115173708.108316-1-brgerst@gmail.com>
References: <20231115173708.108316-1-brgerst@gmail.com>
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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@gmail.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 c4365a05ab83..fab90368481f 100644
--- a/arch/x86/platform/pvh/head.S
+++ b/arch/x86/platform/pvh/head.S
@@ -94,10 +94,15 @@ 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
@@ -156,8 +161,6 @@ 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)
-- 
2.41.0