From: Janakarajan Natarajan Janakarajan.Natarajan@amd.com
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 Janakarajan.Natarajan@amd.com Signed-off-by: Borislav Petkov bp@suse.de Cc: Frederic Weisbecker frederic@kernel.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: Thomas Gleixner tglx@linutronix.de Cc: "x86@kernel.org" x86@kernel.org Cc: Zhenzhong Duan zhenzhong.duan@oracle.com Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20191007190011.4859-1-Janakarajan.Natarajan@amd.co... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/include/asm/mwait.h | 2 +- arch/x86/lib/delay.c | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-)
--- a/arch/x86/include/asm/mwait.h +++ b/arch/x86/include/asm/mwait.h @@ -19,7 +19,7 @@ #define MWAIT_ECX_INTERRUPT_BREAK 0x1 #define MWAITX_ECX_TIMER_ENABLE BIT(1) #define MWAITX_MAX_LOOPS ((u32)-1) -#define MWAITX_DISABLE_CSTATES 0xf +#define MWAITX_DISABLE_CSTATES 0xf0
static inline void __monitor(const void *eax, unsigned long ecx, unsigned long edx) --- a/arch/x86/lib/delay.c +++ b/arch/x86/lib/delay.c @@ -112,8 +112,8 @@ static void delay_mwaitx(unsigned long _ __monitorx(this_cpu_ptr(&cpu_tss), 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);