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Peter Anvin" , David Laight Subject: [PATCH RESEND -tip v2] x86/asm: Improve clflush alternatives assembler template Date: Tue, 5 May 2026 11:50:16 +0200 Message-ID: <20260505095043.3425019-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The inline asm used with alternative_input() specifies the address operand for clflush with the "a" input operand constraint and an explicit "(%[addr])" dereference: "clflush (%[addr])", [addr] "a" (addr) This forces the pointer into %rax and manually encodes the memory operand in the template. Instead, use the %a address operand modifier and relax the constraint from "a" to "r": "clflush %a[addr]", [addr] "r" (addr) This lets the compiler choose the register used for the address and formats the operand as a memory reference. Add a "memory" clobber to ensure the flush is not reordered across memory operations. Signed-off-by: Uros Bizjak Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" Cc: David Laight --- v2: Add "memory" clobber to ensure flush is not reordered across memory operations. --- arch/x86/include/asm/mwait.h | 3 ++- arch/x86/kernel/process.c | 3 ++- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h index e4815e15dc9a..644ada6c0b3b 100644 --- a/arch/x86/include/asm/mwait.h +++ b/arch/x86/include/asm/mwait.h @@ -116,7 +116,8 @@ static __always_inline void mwait_idle_with_hints(u32 eax, u32 ecx) if (static_cpu_has_bug(X86_BUG_MONITOR) || !current_set_polling_and_test()) { const void *addr = ¤t_thread_info()->flags; - alternative_input("", "clflush (%[addr])", X86_BUG_CLFLUSH_MONITOR, [addr] "a" (addr)); + alternative_input("", "clflush %a[addr]", X86_BUG_CLFLUSH_MONITOR, + [addr] "r" (addr) : "memory"); __monitor(addr, 0, 0); if (need_resched()) diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 4c718f8adc59..63581789f7e7 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -921,7 +921,8 @@ static __cpuidle void mwait_idle(void) if (!current_set_polling_and_test()) { const void *addr = ¤t_thread_info()->flags; - alternative_input("", "clflush (%[addr])", X86_BUG_CLFLUSH_MONITOR, [addr] "a" (addr)); + alternative_input("", "clflush %a[addr]", X86_BUG_CLFLUSH_MONITOR, + [addr] "r" (addr) : "memory"); __monitor(addr, 0, 0); if (need_resched()) goto out; -- 2.54.0