linux-kernel - [PATCH] x86/mm/encrypt: Use %a asm operand modifier to obtain %rip-relative address

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Message-ID: <20231120153419.3045-1-ubizjak@gmail.com>
Date:   Mon, 20 Nov 2023 16:33:50 +0100
From:   Uros Bizjak <ubizjak@...il.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Uros Bizjak <ubizjak@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH] x86/mm/encrypt: Use %a asm operand modifier to obtain %rip-relative address

The "a" asm operand modifier substitutes a memory reference, with the
actual operand treated as address.  For x86_64, when a symbol is
provided, the "a" modifier emits "sym(%rip)" instead of "sym".

Clang allows only "i" and "r" operand constraints with an "a" modifier,
so the patch normalizes the modifier/constraint pair to "a"/"i"
which is consistent between both compilers.

No functional change intended.

Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Signed-off-by: Uros Bizjak <ubizjak@...il.com>
---
 arch/x86/mm/mem_encrypt_identity.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index d73aeb16417f..6a351fdd1b39 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -346,9 +346,7 @@ void __init sme_encrypt_kernel(struct boot_params *bp)
 	 * We're running identity mapped, so we must obtain the address to the
 	 * SME encryption workarea using rip-relative addressing.
 	 */
-	asm ("lea sme_workarea(%%rip), %0"
-	     : "=r" (workarea_start)
-	     : "p" (sme_workarea));
+	asm ("lea %a1, %0" : "=r" (workarea_start) : "i" (sme_workarea));
 
 	/*
 	 * Calculate required number of workarea bytes needed:
@@ -582,15 +580,9 @@ void __init sme_enable(struct boot_params *bp)
 	 * identity mapped, so we must obtain the address to the SME command
 	 * line argument data using rip-relative addressing.
 	 */
-	asm ("lea sme_cmdline_arg(%%rip), %0"
-	     : "=r" (cmdline_arg)
-	     : "p" (sme_cmdline_arg));
-	asm ("lea sme_cmdline_on(%%rip), %0"
-	     : "=r" (cmdline_on)
-	     : "p" (sme_cmdline_on));
-	asm ("lea sme_cmdline_off(%%rip), %0"
-	     : "=r" (cmdline_off)
-	     : "p" (sme_cmdline_off));
+	asm ("lea %a1, %0" : "=r" (cmdline_arg) : "i" (sme_cmdline_arg));
+	asm ("lea %a1, %0" : "=r" (cmdline_on) : "i" (sme_cmdline_on));
+	asm ("lea %a1, %0" : "=r" (cmdline_off) : "i" (sme_cmdline_off));
 
 	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT))
 		active_by_default = true;
-- 
2.41.0