From 2722146eb78451b30e4717a267a3a2b44e4ad317 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Wed, 3 Apr 2019 18:41:36 +0200 Subject: x86/fpu: Remove fpu->initialized MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The struct fpu.initialized member is always set to one for user tasks and zero for kernel tasks. This avoids saving/restoring the FPU registers for kernel threads. The ->initialized = 0 case for user tasks has been removed in previous changes, for instance, by doing an explicit unconditional init at fork() time for FPU-less systems which was otherwise delayed until the emulated opcode. The context switch code (switch_fpu_prepare() + switch_fpu_finish()) can't unconditionally save/restore registers for kernel threads. Not only would it slow down the switch but also load a zeroed xcomp_bv for XSAVES. For kernel_fpu_begin() (+end) the situation is similar: EFI with runtime services uses this before alternatives_patched is true. Which means that this function is used too early and it wasn't the case before. For those two cases, use current->mm to distinguish between user and kernel thread. For kernel_fpu_begin() skip save/restore of the FPU registers. During the context switch into a kernel thread don't do anything. There is no reason to save the FPU state of a kernel thread. The reordering in __switch_to() is important because the current() pointer needs to be valid before switch_fpu_finish() is invoked so ->mm is seen of the new task instead the old one. N.B.: fpu__save() doesn't need to check ->mm because it is called by user tasks only. [ bp: Massage. ] Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Borislav Petkov Reviewed-by: Dave Hansen Reviewed-by: Thomas Gleixner Cc: Andy Lutomirski Cc: Aubrey Li Cc: Babu Moger Cc: "Chang S. Bae" Cc: Dmitry Safonov Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Jann Horn Cc: "Jason A. Donenfeld" Cc: Joerg Roedel Cc: kvm ML Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Cc: Nicolai Stange Cc: Paolo Bonzini Cc: Peter Zijlstra Cc: Radim Krčmář Cc: Rik van Riel Cc: Sergey Senozhatsky Cc: Will Deacon Cc: x86-ml Link: https://lkml.kernel.org/r/20190403164156.19645-8-bigeasy@linutronix.de --- arch/x86/include/asm/fpu/internal.h | 18 ++++++++++-------- arch/x86/include/asm/fpu/types.h | 9 --------- 2 files changed, 10 insertions(+), 17 deletions(-) (limited to 'arch/x86/include/asm/fpu') diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h index 70ecb7c032cb..04042eacc852 100644 --- a/arch/x86/include/asm/fpu/internal.h +++ b/arch/x86/include/asm/fpu/internal.h @@ -494,11 +494,14 @@ static inline void fpregs_activate(struct fpu *fpu) * * - switch_fpu_finish() restores the new state as * necessary. + * + * The FPU context is only stored/restored for a user task and + * ->mm is used to distinguish between kernel and user threads. */ static inline void switch_fpu_prepare(struct fpu *old_fpu, int cpu) { - if (static_cpu_has(X86_FEATURE_FPU) && old_fpu->initialized) { + if (static_cpu_has(X86_FEATURE_FPU) && current->mm) { if (!copy_fpregs_to_fpstate(old_fpu)) old_fpu->last_cpu = -1; else @@ -506,8 +509,7 @@ switch_fpu_prepare(struct fpu *old_fpu, int cpu) /* But leave fpu_fpregs_owner_ctx! */ trace_x86_fpu_regs_deactivated(old_fpu); - } else - old_fpu->last_cpu = -1; + } } /* @@ -520,12 +522,12 @@ switch_fpu_prepare(struct fpu *old_fpu, int cpu) */ static inline void switch_fpu_finish(struct fpu *new_fpu, int cpu) { - bool preload = static_cpu_has(X86_FEATURE_FPU) && - new_fpu->initialized; + if (static_cpu_has(X86_FEATURE_FPU)) { + if (!fpregs_state_valid(new_fpu, cpu)) { + if (current->mm) + copy_kernel_to_fpregs(&new_fpu->state); + } - if (preload) { - if (!fpregs_state_valid(new_fpu, cpu)) - copy_kernel_to_fpregs(&new_fpu->state); fpregs_activate(new_fpu); } } diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h index 2e32e178e064..f098f6cab94b 100644 --- a/arch/x86/include/asm/fpu/types.h +++ b/arch/x86/include/asm/fpu/types.h @@ -293,15 +293,6 @@ struct fpu { */ unsigned int last_cpu; - /* - * @initialized: - * - * This flag indicates whether this context is initialized: if the task - * is not running then we can restore from this context, if the task - * is running then we should save into this context. - */ - unsigned char initialized; - /* * @avx512_timestamp: * -- cgit v1.2.3