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authorSebastian Andrzej Siewior <bigeasy@linutronix.de>2019-04-03 18:41:36 +0200
committerBorislav Petkov <bp@suse.de>2019-04-10 15:42:40 +0200
commit2722146eb78451b30e4717a267a3a2b44e4ad317 (patch)
tree9e1182428d9bcb6f6034d156c9a068ccd98f7cdb /arch/x86/kernel/process_32.c
parent39388e80f9b0c3788bfb6efe3054bdce0c3ead45 (diff)
x86/fpu: Remove fpu->initialized
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 <bigeasy@linutronix.de> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Dave Hansen <dave.hansen@intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Andy Lutomirski <luto@kernel.org> Cc: Aubrey Li <aubrey.li@intel.com> Cc: Babu Moger <Babu.Moger@amd.com> Cc: "Chang S. Bae" <chang.seok.bae@intel.com> Cc: Dmitry Safonov <dima@arista.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jann Horn <jannh@google.com> Cc: "Jason A. Donenfeld" <Jason@zx2c4.com> Cc: Joerg Roedel <jroedel@suse.de> Cc: kvm ML <kvm@vger.kernel.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Nicolai Stange <nstange@suse.de> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Radim Krčmář <rkrcmar@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Will Deacon <will.deacon@arm.com> Cc: x86-ml <x86@kernel.org> Link: https://lkml.kernel.org/r/20190403164156.19645-8-bigeasy@linutronix.de
Diffstat (limited to 'arch/x86/kernel/process_32.c')
-rw-r--r--arch/x86/kernel/process_32.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 7888a41a03cd..77d9eb43ccac 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -288,10 +288,10 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
if (prev->gs | next->gs)
lazy_load_gs(next->gs);
- switch_fpu_finish(next_fpu, cpu);
-
this_cpu_write(current_task, next_p);
+ switch_fpu_finish(next_fpu, cpu);
+
/* Load the Intel cache allocation PQR MSR. */
resctrl_sched_in();