From: Sebastian Andrzej Siewior Date: Tue, 2 Apr 2019 13:02:25 +0200 Subject: [PATCH 24/27] x86/fpu: Add a fastpath to __fpu__restore_sig() Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.0/older/patches-5.0.10-rt7.tar.xz The previous commits refactor the restoration of the FPU registers so that they can be loaded from in-kernel memory. This overhead can be avoided if the load can be performed without a pagefault. Attempt to restore FPU registers by invoking copy_user_to_fpregs_zeroing(). If it fails try the slowpath which can handle pagefaults. Signed-off-by: Sebastian Andrzej Siewior --- arch/x86/kernel/fpu/signal.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -242,10 +242,10 @@ sanitize_restored_xstate(union fpregs_st /* * Restore the extended state if present. Otherwise, restore the FP/SSE state. */ -static inline int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only) +static int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only) { if (use_xsave()) { - if ((unsigned long)buf % 64 || fx_only) { + if (fx_only) { u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE; copy_kernel_to_xregs(&init_fpstate.xsave, init_bv); return copy_user_to_fxregs(buf); @@ -327,7 +327,19 @@ static int __fpu__restore_sig(void __use if (ret) goto err_out; envp = &env; + } else { + fpregs_lock(); + pagefault_disable(); + ret = copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only); + pagefault_enable(); + if (!ret) { + fpregs_mark_activate(); + fpregs_unlock(); + return 0; + } + fpregs_unlock(); } + if (use_xsave() && !fx_only) { u64 init_bv = xfeatures_mask & ~xfeatures;