From: Cyril Bur Date: Mon, 29 Feb 2016 06:53:46 +0000 (+1100) Subject: powerpc: Explicitly disable math features when copying thread X-Git-Tag: v4.6-rc1~89^2~62 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=d272f6670a0bcc91fa50c234088d21cd6ac30af4;p=linux.git powerpc: Explicitly disable math features when copying thread Currently when threads get scheduled off they always giveup the FPU, Altivec (VMX) and Vector (VSX) units if they were using them. When they are scheduled back on a fault is then taken to enable each facility and load registers. As a result explicitly disabling FPU/VMX/VSX has not been necessary. Future changes and optimisations remove this mandatory giveup and fault which could cause calls such as clone() and fork() to copy threads and run them later with FPU/VMX/VSX enabled but no registers loaded. This patch starts the process of having MSR_{FP,VEC,VSX} mean that a threads registers are hot while not having MSR_{FP,VEC,VSX} means that the registers must be loaded. This allows for a smarter return to userspace. Signed-off-by: Cyril Bur Signed-off-by: Michael Ellerman --- diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index dccc87e8fee5..e0c3d2dc7ca3 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1307,6 +1307,7 @@ int copy_thread(unsigned long clone_flags, unsigned long usp, f = ret_from_fork; } + childregs->msr &= ~(MSR_FP|MSR_VEC|MSR_VSX); sp -= STACK_FRAME_OVERHEAD; /*