[PATCH v2] x86/smpboot: Don't do mwait_play_dead() on AMD systems

[PATCH v2] x86/smpboot: Don't do mwait_play_dead() on AMD systems

[Yazen Ghannam]

From: Yazen Ghannam <yazen.ghannam@amd.com>

Recent AMD systems support using MWAIT for C1 state. However, MWAIT will
not allow deeper cstates than C1 on current systems.

With play_dead() we expect the OS to use the deepest state available.
The deepest state available on AMD systems is reached through SystemIO
or HALT. If MWAIT is available, we use it instead of the other methods,
so we never reach the deepest state.

Don't try to use MWAIT to play_dead() on AMD systems. Instead, we'll use
CPUIDLE to enter the deepest state advertised by firmware. If CPUIDLE is
not available then we fallback to HALT.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
---
Link:
https://lkml.kernel.org/r/20180402183424.48222-1-Yazen.Ghannam@amd.com

v1->v2:
* Drop comment in code.

 arch/x86/kernel/smpboot.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index ff99e2b6fc54..12599e55e040 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1536,6 +1536,8 @@ static inline void mwait_play_dead(void)
 	void *mwait_ptr;
 	int i;
 
+	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
+		return;
 	if (!this_cpu_has(X86_FEATURE_MWAIT))
 		return;
 	if (!this_cpu_has(X86_FEATURE_CLFLUSH))
-- 
2.14.1

Re: [PATCH v2] x86/smpboot: Don't do mwait_play_dead() on AMD systems

[Borislav Petkov]

On Tue, Apr 03, 2018 at 09:02:28AM -0500, Yazen Ghannam wrote:
> From: Yazen Ghannam <yazen.ghannam@amd.com>
> 
> Recent AMD systems support using MWAIT for C1 state. However, MWAIT will
> not allow deeper cstates than C1 on current systems.
> 
> With play_dead() we expect the OS to use the deepest state available.
> The deepest state available on AMD systems is reached through SystemIO
> or HALT. If MWAIT is available, we use it instead of the other methods,
> so we never reach the deepest state.
> 
> Don't try to use MWAIT to play_dead() on AMD systems. Instead, we'll use
> CPUIDLE to enter the deepest state advertised by firmware. If CPUIDLE is
> not available then we fallback to HALT.
> 
> Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
> ---
> Link:
> https://lkml.kernel.org/r/20180402183424.48222-1-Yazen.Ghannam@amd.com
> 
> v1->v2:
> * Drop comment in code.
> 
>  arch/x86/kernel/smpboot.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index ff99e2b6fc54..12599e55e040 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1536,6 +1536,8 @@ static inline void mwait_play_dead(void)
>  	void *mwait_ptr;
>  	int i;
>  
> +	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
> +		return;
>  	if (!this_cpu_has(X86_FEATURE_MWAIT))
>  		return;
>  	if (!this_cpu_has(X86_FEATURE_CLFLUSH))
> -- 

Reviewed-by: Borislav Petkov <bp@suse.de>

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 

[tip:x86/urgent] x86/smpboot: Don't use mwait_play_dead() on AMD systems

[tip-bot for Yazen Ghannam]

Commit-ID:  da6fa7ef67f07108a1b0cb9fd9e7fcaabd39c051
Gitweb:     https://git.kernel.org/tip/da6fa7ef67f07108a1b0cb9fd9e7fcaabd39c051
Author:     Yazen Ghannam <yazen.ghannam@amd.com>
AuthorDate: Tue, 3 Apr 2018 09:02:28 -0500
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 26 Apr 2018 16:06:19 +0200

x86/smpboot: Don't use mwait_play_dead() on AMD systems

Recent AMD systems support using MWAIT for C1 state. However, MWAIT will
not allow deeper cstates than C1 on current systems.

play_dead() expects to use the deepest state available.  The deepest state
available on AMD systems is reached through SystemIO or HALT. If MWAIT is
available, it is preferred over the other methods, so the CPU never reaches
the deepest possible state.

Don't try to use MWAIT to play_dead() on AMD systems. Instead, use CPUIDLE
to enter the deepest state advertised by firmware. If CPUIDLE is not
available then fallback to HALT.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org
Cc: Yazen Ghannam <Yazen.Ghannam@amd.com>
Link: https://lkml.kernel.org/r/20180403140228.58540-1-Yazen.Ghannam@amd.com

---
 arch/x86/kernel/smpboot.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 45175b81dd5b..0f1cbb042f49 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1571,6 +1571,8 @@ static inline void mwait_play_dead(void)
 	void *mwait_ptr;
 	int i;
 
+	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
+		return;
 	if (!this_cpu_has(X86_FEATURE_MWAIT))
 		return;
 	if (!this_cpu_has(X86_FEATURE_CLFLUSH))