linux-kernel - [tip: x86/fpu] intel_idle: Add a new flag to initialize the AMX state

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Date:   Tue, 19 Jul 2022 17:31:10 -0000
From:   "tip-bot2 for Chang S. Bae" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Borislav Petkov <bp@...e.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Zhang Rui <rui.zhang@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/fpu] intel_idle: Add a new flag to initialize the AMX state

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     9f01129382774d98ec21526f13da26a0630ee3d8
Gitweb:        https://git.kernel.org/tip/9f01129382774d98ec21526f13da26a0630ee3d8
Author:        Chang S. Bae <chang.seok.bae@...el.com>
AuthorDate:    Mon, 18 Jul 2022 11:56:11 -07:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Tue, 19 Jul 2022 19:17:28 +02:00

intel_idle: Add a new flag to initialize the AMX state

The non-initialized AMX state can be the cause of C-state demotion from C6
to C1E. This low-power idle state may improve power savings and thus result
in a higher available turbo frequency budget.

This behavior is implementation-specific. Initialize the state for the C6
entrance of Sapphire Rapids as needed.

Suggested-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Tested-by: Zhang Rui <rui.zhang@...el.com>
Link: https://lkml.kernel.org/r/20220614164116.5196-1-chang.seok.bae@intel.com
---
 drivers/idle/intel_idle.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index f5c6802..1ec2210 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -56,6 +56,7 @@
 #include <asm/nospec-branch.h>
 #include <asm/mwait.h>
 #include <asm/msr.h>
+#include <asm/fpu/api.h>
 
 #define INTEL_IDLE_VERSION "0.5.1"
 
@@ -114,6 +115,11 @@ static unsigned int mwait_substates __initdata;
 #define CPUIDLE_FLAG_IBRS		BIT(16)
 
 /*
+ * Initialize large xstate for the C6-state entrance.
+ */
+#define CPUIDLE_FLAG_INIT_XSTATE	BIT(17)
+
+/*
  * MWAIT takes an 8-bit "hint" in EAX "suggesting"
  * the C-state (top nibble) and sub-state (bottom nibble)
  * 0x00 means "MWAIT(C1)", 0x10 means "MWAIT(C2)" etc.
@@ -185,6 +191,13 @@ static __cpuidle int intel_idle_ibrs(struct cpuidle_device *dev,
 	return ret;
 }
 
+static __cpuidle int intel_idle_xstate(struct cpuidle_device *dev,
+				       struct cpuidle_driver *drv, int index)
+{
+	fpu_idle_fpregs();
+	return __intel_idle(dev, drv, index);
+}
+
 /**
  * intel_idle_s2idle - Ask the processor to enter the given idle state.
  * @dev: cpuidle device of the target CPU.
@@ -200,8 +213,12 @@ static __cpuidle int intel_idle_ibrs(struct cpuidle_device *dev,
 static __cpuidle int intel_idle_s2idle(struct cpuidle_device *dev,
 				       struct cpuidle_driver *drv, int index)
 {
-	unsigned long eax = flg2MWAIT(drv->states[index].flags);
 	unsigned long ecx = 1; /* break on interrupt flag */
+	struct cpuidle_state *state = &drv->states[index];
+	unsigned long eax = flg2MWAIT(state->flags);
+
+	if (state->flags & CPUIDLE_FLAG_INIT_XSTATE)
+		fpu_idle_fpregs();
 
 	mwait_idle_with_hints(eax, ecx);
 
@@ -936,7 +953,8 @@ static struct cpuidle_state spr_cstates[] __initdata = {
 	{
 		.name = "C6",
 		.desc = "MWAIT 0x20",
-		.flags = MWAIT2flg(0x20) | CPUIDLE_FLAG_TLB_FLUSHED,
+		.flags = MWAIT2flg(0x20) | CPUIDLE_FLAG_TLB_FLUSHED |
+					   CPUIDLE_FLAG_INIT_XSTATE,
 		.exit_latency = 290,
 		.target_residency = 800,
 		.enter = &intel_idle,
@@ -1851,6 +1869,9 @@ static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
 			drv->states[drv->state_count].enter = intel_idle_ibrs;
 		}
 
+		if (cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_INIT_XSTATE)
+			drv->states[drv->state_count].enter = intel_idle_xstate;
+
 		if ((disabled_states_mask & BIT(drv->state_count)) ||
 		    ((icpu->use_acpi || force_use_acpi) &&
 		     intel_idle_off_by_default(mwait_hint) &&