From 58cd9be912c3f8c2d29f3a8bb73badfbe739dfb6 Mon Sep 17 00:00:00 2001 From: Janakarajan Natarajan Date: Mon, 7 Oct 2019 19:00:22 +0000 Subject: x86/asm: Fix MWAITX C-state hint value commit 454de1e7d970d6bc567686052329e4814842867c upstream. As per "AMD64 Architecture Programmer's Manual Volume 3: General-Purpose and System Instructions", MWAITX EAX[7:4]+1 specifies the optional hint of the optimized C-state. For C0 state, EAX[7:4] should be set to 0xf. Currently, a value of 0xf is set for EAX[3:0] instead of EAX[7:4]. Fix this by changing MWAITX_DISABLE_CSTATES from 0xf to 0xf0. This hasn't had any implications so far because setting reserved bits in EAX is simply ignored by the CPU. [ bp: Fixup comment in delay_mwaitx() and massage. ] Signed-off-by: Janakarajan Natarajan Signed-off-by: Borislav Petkov Cc: Frederic Weisbecker Cc: Greg Kroah-Hartman Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Thomas Gleixner Cc: "x86@kernel.org" Cc: Zhenzhong Duan Cc: Link: https://lkml.kernel.org/r/20191007190011.4859-1-Janakarajan.Natarajan@amd.com Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- arch/x86/lib/delay.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/x86/lib/delay.c') diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c index b7375dc6898f..c126571e5e2e 100644 --- a/arch/x86/lib/delay.c +++ b/arch/x86/lib/delay.c @@ -113,8 +113,8 @@ static void delay_mwaitx(unsigned long __loops) __monitorx(raw_cpu_ptr(&cpu_tss_rw), 0, 0); /* - * AMD, like Intel, supports the EAX hint and EAX=0xf - * means, do not enter any deep C-state and we use it + * AMD, like Intel's MWAIT version, supports the EAX hint and + * EAX=0xf0 means, do not enter any deep C-state and we use it * here in delay() to minimize wakeup latency. */ __mwaitx(MWAITX_DISABLE_CSTATES, delay, MWAITX_ECX_TIMER_ENABLE); -- cgit v1.2.3