From f17b168734c0fe47343a7502d012266a051f9942 Mon Sep 17 00:00:00 2001 From: "Chang S. Bae" Date: Wed, 8 Jun 2022 09:47:47 -0700 Subject: [PATCH] x86/fpu: Add a helper to prepare AMX state for low-power CPU idle 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 Signed-off-by: Dave Hansen Signed-off-by: Borislav Petkov Link: https://lkml.kernel.org/r/20220608164748.11864-2-chang.seok.bae@intel.com --- 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(+) diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h index 6b0f31f..503a577 100644 --- a/arch/x86/include/asm/fpu/api.h +++ b/arch/x86/include/asm/fpu/api.h @@ -164,4 +164,6 @@ static inline bool fpstate_is_confidential(struct fpu_guest *gfpu) /* prctl */ extern long fpu_xstate_prctl(int option, unsigned long arg2); +extern void fpu_idle_fpregs(void); + #endif /* _ASM_X86_FPU_API_H */ diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h index 45b18eb..35f709f 100644 --- a/arch/x86/include/asm/special_insns.h +++ b/arch/x86/include/asm/special_insns.h @@ -295,6 +295,15 @@ static inline int enqcmds(void __iomem *dst, const void *src) 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 */ diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 0531d6a..3b28c5b 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -851,3 +851,17 @@ int fpu__exception_code(struct fpu *fpu, int trap_nr) */ 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(¤t->thread.fpu); + } +} -- 2.7.4