x86/asm: Fix MWAITX C-state hint value

BugLink: https://bugs.launchpad.net/bugs/1850541
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.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index eb0f80ce8524d415884d11ecbe555e6a778edfa5..3aa82deeab5ae862111e242138267bb53ddc622a 100644 (file)
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -21,7 +21,7 @@
 #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)

diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c
index 4846eff7e4c8b1505501d7f1dcb64127d0a4c67c..17a0d0f5a1bf4f2fd15ccba6bcba03ae36bdb31f 100644 (file)
--- 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);