From: "Chang S. Bae" <chang.seok.bae@intel.com>
Date: Wed, 8 Jun 2022 09:47:47 -0700
Subject: x86/fpu: Add a helper to prepare AMX state for low-power CPU idle
Git-commit: f17b168734c0fe47343a7502d012266a051f9942
Patch-mainline: 6.0-rc1
References: jsc#PED-1038

When a CPU enters an idle state, a non-initialized AMX register state may
be the cause of preventing a deeper low-power state. Other extended
register states whether initialized or not do not impact the CPU idle
state.

The new helper can ensure the AMX state is initialized before the CPU is
idle, and it will be used by the intel idle driver.

Check the AMX_TILE feature bit before using XGETBV1 as a chain of
dependencies was established via cpuid_deps[]: AMX->XFD->XGETBV1.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20220608164748.11864-2-chang.seok.bae@intel.com
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 arch/x86/include/asm/fpu/api.h       |    2 ++
 arch/x86/include/asm/special_insns.h |    9 +++++++++
 arch/x86/kernel/fpu/core.c           |   14 ++++++++++++++
 3 files changed, 25 insertions(+)

--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -162,4 +162,6 @@ static inline bool fpstate_is_confidenti
 struct task_struct;
 extern long fpu_xstate_prctl(struct task_struct *tsk, int option, unsigned long arg2);
 
+extern void fpu_idle_fpregs(void);
+
 #endif /* _ASM_X86_FPU_API_H */
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -294,6 +294,15 @@ static inline int enqcmds(void __iomem *
 	return 0;
 }
 
+static inline void tile_release(void)
+{
+	/*
+	 * Instruction opcode for TILERELEASE; supported in binutils
+	 * version >= 2.36.
+	 */
+	asm volatile(".byte 0xc4, 0xe2, 0x78, 0x49, 0xc0");
+}
+
 #endif /* __KERNEL__ */
 
 #endif /* _ASM_X86_SPECIAL_INSNS_H */
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -759,3 +759,17 @@ int fpu__exception_code(struct fpu *fpu,
 	 */
 	return 0;
 }
+
+/*
+ * Initialize register state that may prevent from entering low-power idle.
+ * This function will be invoked from the cpuidle driver only when needed.
+ */
+void fpu_idle_fpregs(void)
+{
+	/* Note: AMX_TILE being enabled implies XGETBV1 support */
+	if (cpu_feature_enabled(X86_FEATURE_AMX_TILE) &&
+	    (xfeatures_in_use() & XFEATURE_MASK_XTILE)) {
+		tile_release();
+		fpregs_deactivate(&current->thread.fpu);
+	}
+}