linux-kernel - [PATCH RESEND -tip] x86/percpu: Use %RIP-relative address in untagged

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Message-ID: <20231213150357.5942-1-ubizjak@gmail.com>
Date:   Wed, 13 Dec 2023 16:03:15 +0100
From:   Uros Bizjak <ubizjak@...il.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Uros Bizjak <ubizjak@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radaed.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH RESEND -tip] x86/percpu: Use %RIP-relative address in untagged_addr()

%RIP-relative addresses are nowadays correctly handled in alternative
instructions, so remove misleading comment and improve assembly to
use %RIP-relative address.

Also, explicitly using %gs: prefix will segfault for non-SMP builds.
Use macros from percpu.h which will DTRT with segment prefix register
as far as SMP/non-SMP builds are concerned.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radaed.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Signed-off-by: Uros Bizjak <ubizjak@...il.com>
---
 arch/x86/include/asm/uaccess_64.h | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h
index f2c02e4469cc..01455c0b070c 100644
--- a/arch/x86/include/asm/uaccess_64.h
+++ b/arch/x86/include/asm/uaccess_64.h
@@ -11,6 +11,7 @@
 #include <asm/alternative.h>
 #include <asm/cpufeatures.h>
 #include <asm/page.h>
+#include <asm/percpu.h>
 
 #ifdef CONFIG_ADDRESS_MASKING
 /*
@@ -18,14 +19,10 @@
  */
 static inline unsigned long __untagged_addr(unsigned long addr)
 {
-	/*
-	 * Refer tlbstate_untag_mask directly to avoid RIP-relative relocation
-	 * in alternative instructions. The relocation gets wrong when gets
-	 * copied to the target place.
-	 */
 	asm (ALTERNATIVE("",
-			 "and %%gs:tlbstate_untag_mask, %[addr]\n\t", X86_FEATURE_LAM)
-	     : [addr] "+r" (addr) : "m" (tlbstate_untag_mask));
+			 "and " __percpu_arg([mask]) ", %[addr]", X86_FEATURE_LAM)
+	     : [addr] "+r" (addr)
+	     : [mask] "m" (__my_cpu_var(tlbstate_untag_mask)));
 
 	return addr;
 }
-- 
2.42.0