x86: Remove __FORCE_ORDER workaround

GCC PR82602 that caused invalid scheduling of volatile asms:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82602

was fixed for gcc-8.1.0, the current minimum version of the
compiler required to compile the kernel.

Remove workaround that prevented invalid scheduling for
compilers, affected by PR82602.

There were no differences between old and new kernel object file
when compiled for x86_64 defconfig with gcc-8.1.0.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20250407112316.378347-1-ubizjak@gmail.com

1 files changed, 6 insertions, 6 deletions

diff --git a/arch/x86/include/asm/debugreg.h b/arch/x86/include/asm/debugreg.h
index fdbbbfec745a..719d95f1ab5e 100644
--- a/arch/x86/include/asm/debugreg.h
+++ b/arch/x86/include/asm/debugreg.h
@@ -23,7 +23,7 @@ DECLARE_PER_CPU(unsigned long, cpu_dr7);
 
 static __always_inline unsigned long native_get_debugreg(int regno)
 {
-	unsigned long val = 0;	/* Damn you, gcc! */
+	unsigned long val;
 
 	switch (regno) {
 	case 0:
@@ -43,7 +43,7 @@ static __always_inline unsigned long native_get_debugreg(int regno)
 		break;
 	case 7:
 		/*
-		 * Apply __FORCE_ORDER to DR7 reads to forbid re-ordering them
+		 * Use "asm volatile" for DR7 reads to forbid re-ordering them
 		 * with other code.
 		 *
 		 * This is needed because a DR7 access can cause a #VC exception
@@ -55,7 +55,7 @@ static __always_inline unsigned long native_get_debugreg(int regno)
 		 * re-ordered to happen before the call to sev_es_ist_enter(),
 		 * causing stack recursion.
 		 */
-		asm volatile("mov %%db7, %0" : "=r" (val) : __FORCE_ORDER);
+		asm volatile("mov %%db7, %0" : "=r" (val));
 		break;
 	default:
 		BUG();
@@ -83,15 +83,15 @@ static __always_inline void native_set_debugreg(int regno, unsigned long value)
 		break;
 	case 7:
 		/*
-		 * Apply __FORCE_ORDER to DR7 writes to forbid re-ordering them
+		 * Use "asm volatile" for DR7 writes to forbid re-ordering them
 		 * with other code.
 		 *
 		 * While is didn't happen with a DR7 write (see the DR7 read
 		 * comment above which explains where it happened), add the
-		 * __FORCE_ORDER here too to avoid similar problems in the
+		 * "asm volatile" here too to avoid similar problems in the
 		 * future.
 		 */
-		asm volatile("mov %0, %%db7"	::"r" (value), __FORCE_ORDER);
+		asm volatile("mov %0, %%db7"	::"r" (value));
 		break;
 	default:
 		BUG();