From 0169f53e0d97bb675075506810494bd86b8c934e Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Wed, 3 Apr 2019 18:41:37 +0200 Subject: [PATCH] x86/fpu: Remove user_fpu_begin() MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit user_fpu_begin() sets fpu_fpregs_owner_ctx to task's fpu struct. This is always the case since there is no lazy FPU anymore. fpu_fpregs_owner_ctx is used during context switch to decide if it needs to load the saved registers or if the currently loaded registers are valid. It could be skipped during a taskA -> kernel thread -> taskA switch because the switch to the kernel thread would not alter the CPU's sFPU tate. Since this field is always updated during context switch and never invalidated, setting it manually (in user context) makes no difference. A kernel thread with kernel_fpu_begin() block could set fpu_fpregs_owner_ctx to NULL but a kernel thread does not use user_fpu_begin(). This is a leftover from the lazy-FPU time. Remove user_fpu_begin(), it does not change fpu_fpregs_owner_ctx's content. Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Borislav Petkov Reviewed-by: Borislav Petkov Reviewed-by: Dave Hansen Reviewed-by: Thomas Gleixner Cc: Andy Lutomirski Cc: Aubrey Li Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Jann Horn Cc: "Jason A. Donenfeld" Cc: kvm ML Cc: Nicolai Stange Cc: Paolo Bonzini Cc: Radim Krčmář Cc: Rik van Riel Cc: x86-ml Link: https://lkml.kernel.org/r/20190403164156.19645-9-bigeasy@linutronix.de --- arch/x86/include/asm/fpu/internal.h | 17 ----------------- arch/x86/kernel/fpu/core.c | 4 +--- arch/x86/kernel/fpu/signal.c | 1 - 3 files changed, 1 insertion(+), 21 deletions(-) diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h index 04042ea..54f70ca 100644 --- a/arch/x86/include/asm/fpu/internal.h +++ b/arch/x86/include/asm/fpu/internal.h @@ -533,23 +533,6 @@ static inline void switch_fpu_finish(struct fpu *new_fpu, int cpu) } /* - * Needs to be preemption-safe. - * - * NOTE! user_fpu_begin() must be used only immediately before restoring - * the save state. It does not do any saving/restoring on its own. In - * lazy FPU mode, it is just an optimization to avoid a #NM exception, - * the task can lose the FPU right after preempt_enable(). - */ -static inline void user_fpu_begin(void) -{ - struct fpu *fpu = ¤t->thread.fpu; - - preempt_disable(); - fpregs_activate(fpu); - preempt_enable(); -} - -/* * MXCSR and XCR definitions: */ diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 97e27de..739ca3a 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -335,10 +335,8 @@ void fpu__clear(struct fpu *fpu) * Make sure fpstate is cleared and initialized. */ fpu__initialize(fpu); - if (static_cpu_has(X86_FEATURE_FPU)) { - user_fpu_begin(); + if (static_cpu_has(X86_FEATURE_FPU)) copy_init_fpstate_to_fpregs(); - } } /* diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c index 34989d2..155f455 100644 --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -322,7 +322,6 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) * For 64-bit frames and 32-bit fsave frames, restore the user * state to the registers directly (with exceptions handled). */ - user_fpu_begin(); if (copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only)) { fpu__clear(fpu); return -1; -- 2.7.4