From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastian Andrzej Siewior Subject: [PATCH 06/27] x86/fpu: Don't save fxregs for ia32 frames in copy_fpstate_to_sigframe() Date: Wed, 3 Apr 2019 18:41:35 +0200 Message-ID: <20190403164156.19645-7-bigeasy@linutronix.de> References: <20190403164156.19645-1-bigeasy@linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Cc: x86@kernel.org, Andy Lutomirski , Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= , kvm@vger.kernel.org, "Jason A. Donenfeld" , Rik van Riel , Dave Hansen , Sebastian Andrzej Siewior To: linux-kernel@vger.kernel.org Return-path: In-Reply-To: <20190403164156.19645-1-bigeasy@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org In commit 72a671ced66db ("x86, fpu: Unify signal handling code paths for x86 and x86_64 kernels") the 32bit and 64bit path of the signal delivery code were merged. The 32bit version: |int save_i387_xstate_ia32(void __user *buf) |… | if (cpu_has_xsave) | return save_i387_xsave(fp); | if (cpu_has_fxsr) | return save_i387_fxsave(fp); The 64bit version: |int save_i387_xstate(void __user *buf) |… | if (user_has_fpu()) { | if (use_xsave()) | err = xsave_user(buf); | else | err = fxsave_user(buf); | | if (unlikely(err)) { | __clear_user(buf, xstate_size); | return err; The merge: |int save_xstate_sig(void __user *buf, void __user *buf_fx, int size) |… | if (user_has_fpu()) { | /* Save the live register state to the user directly. */ | if (save_user_xstate(buf_fx)) | return -1; | /* Update the thread's fxstate to save the fsave header. */ | if (ia32_fxstate) | fpu_fxsave(&tsk->thread.fpu); I don't think that we needed to save the FPU registers to ->thread.fpu because the registers were stored in `buf_fx'. Today the state will be restored from `buf_fx' after the signal was handled (I assume that this was also the case with lazy-FPU). Since commit 66463db4fc560 ("x86, fpu: shift drop_init_fpu() from save_xstate_sig() to handle_signal()") it is ensured that the signal handler starts with clear/fresh set of FPU registers which means that the previous store is futile. Remove copy_fxregs_to_kernel() because task's FPU state is cleared later in handle_signal() via fpu__clear(). Signed-off-by: Sebastian Andrzej Siewior --- arch/x86/kernel/fpu/signal.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c index de83d0ed9e14e..2f044021fde2b 100644 --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -155,7 +155,6 @@ static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf) */ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size) { - struct fpu *fpu = ¤t->thread.fpu; struct task_struct *tsk = current; int ia32_fxstate = (buf != buf_fx); @@ -173,9 +172,6 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size) /* Save the live register state to the user directly. */ if (copy_fpregs_to_sigframe(buf_fx)) return -1; - /* Update the thread's fxstate to save the fsave header. */ - if (ia32_fxstate) - copy_fxregs_to_kernel(fpu); /* Save the fsave header for the 32-bit frames. */ if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf)) -- 2.20.1