linux-kernel - [PATCH v3 15/17] x86/compressed: adhere to calling convention in get_sev_encryption

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Date:   Tue, 22 Nov 2022 17:10:15 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-efi@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Michael Roth <michael.roth@....com>
Subject: [PATCH v3 15/17] x86/compressed: adhere to calling convention in get_sev_encryption_bit()

Make get_sev_encryption_bit() follow the ordinary i386 calling
convention, and only call it if CONFIG_AMD_MEM_ENCRYPT is actually
enabled. This clarifies the calling code, and makes it more
maintainable.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/boot/compressed/head_64.S     |  5 +++--
 arch/x86/boot/compressed/mem_encrypt.S | 10 ----------
 2 files changed, 3 insertions(+), 12 deletions(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 0cfc8ce273a2731c..dd18216cff5c37e0 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -188,12 +188,13 @@ SYM_FUNC_START(startup_32)
   */
 	/*
 	 * If SEV is active then set the encryption mask in the page tables.
-	 * This will insure that when the kernel is copied and decompressed
+	 * This will ensure that when the kernel is copied and decompressed
 	 * it will be done so encrypted.
 	 */
-	call	get_sev_encryption_bit
 	xorl	%edx, %edx
 #ifdef	CONFIG_AMD_MEM_ENCRYPT
+	call	get_sev_encryption_bit
+	xorl	%edx, %edx
 	testl	%eax, %eax
 	jz	1f
 	subl	$32, %eax	/* Encryption bit is always above bit 31 */
diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S
index 14cf04a1ed091655..e69674588a31c81f 100644
--- a/arch/x86/boot/compressed/mem_encrypt.S
+++ b/arch/x86/boot/compressed/mem_encrypt.S
@@ -18,12 +18,7 @@
 	.text
 	.code32
 SYM_FUNC_START(get_sev_encryption_bit)
-	xor	%eax, %eax
-
-#ifdef CONFIG_AMD_MEM_ENCRYPT
 	push	%ebx
-	push	%ecx
-	push	%edx
 
 	movl	$0x80000000, %eax	/* CPUID to check the highest leaf */
 	cpuid
@@ -54,12 +49,7 @@ SYM_FUNC_START(get_sev_encryption_bit)
 	xor	%eax, %eax
 
 .Lsev_exit:
-	pop	%edx
-	pop	%ecx
 	pop	%ebx
-
-#endif	/* CONFIG_AMD_MEM_ENCRYPT */
-
 	RET
 SYM_FUNC_END(get_sev_encryption_bit)
 
-- 
2.35.1