Merge tag 'x86-fpu-2023-02-20' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fpu updates from Ingo Molnar:

 - Replace zero-length array in struct xregs_state with flexible-array
   member, to help the enabling of stricter compiler checks.

 - Don't set TIF_NEED_FPU_LOAD for PF_IO_WORKER threads.

* tag 'x86-fpu-2023-02-20' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/fpu: Don't set TIF_NEED_FPU_LOAD for PF_IO_WORKER threads
  x86/fpu: Replace zero-length array in struct xregs_state with flexible-array member

Author: torvalds

arch/x86/include/asm/fpu/sched.h

@@ -39,7 +39,7 @@ extern void fpu_flush_thread(void);
 static inline void switch_fpu_prepare(struct fpu *old_fpu, int cpu)
 {
 	if (cpu_feature_enabled(X86_FEATURE_FPU) &&
-	    !(current->flags & PF_KTHREAD)) {
+	    !(current->flags & (PF_KTHREAD | PF_IO_WORKER))) {
 		save_fpregs_to_fpstate(old_fpu);
 		/*
 		 * The save operation preserved register state, so the

arch/x86/include/asm/fpu/types.h

@@ -321,7 +321,7 @@ struct xstate_header {
 struct xregs_state {
 	struct fxregs_state		i387;
 	struct xstate_header		header;
-	u8				extended_state_area[0];
+	u8				extended_state_area[];
 } __attribute__ ((packed, aligned (64)));
 
 /*

arch/x86/kernel/fpu/context.h

@@ -57,7 +57,7 @@ static inline void fpregs_restore_userregs(void)
 	struct fpu *fpu = &current->thread.fpu;
 	int cpu = smp_processor_id();
 
-	if (WARN_ON_ONCE(current->flags & PF_KTHREAD))
+	if (WARN_ON_ONCE(current->flags & (PF_KTHREAD | PF_IO_WORKER)))
 		return;
 
 	if (!fpregs_state_valid(fpu, cpu)) {

arch/x86/kernel/fpu/core.c

@@ -426,7 +426,7 @@ void kernel_fpu_begin_mask(unsigned int kfpu_mask)
 
 	this_cpu_write(in_kernel_fpu, true);
 
-	if (!(current->flags & PF_KTHREAD) &&
+	if (!(current->flags & (PF_KTHREAD | PF_IO_WORKER)) &&
 	    !test_thread_flag(TIF_NEED_FPU_LOAD)) {
 		set_thread_flag(TIF_NEED_FPU_LOAD);
 		save_fpregs_to_fpstate(&current->thread.fpu);