x86/fpu: Change fpu->fpregs_active users to fpu->fpstate_active

We want to simplify the FPU state machine by eliminating fpu->fpregs_active,
and we can do that because the two state flags (::fpregs_active and
::fpstate_active) are set essentially together.

The old lazy FPU switching code used to make a distinction - but there's
no lazy switching code anymore, we always switch in an 'eager' fashion.

Do this by first changing all substantial uses of fpu->fpregs_active
to fpu->fpstate_active and adding a few debug checks to double check
our assumption is correct.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/20170923130016.21448-19-mingo@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

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

@@ -556,7 +556,9 @@ static inline void fpregs_activate(struct fpu *fpu)
 static inline void
 switch_fpu_prepare(struct fpu *old_fpu, int cpu)
 {
-	if (old_fpu->fpregs_active) {
+	WARN_ON_FPU(old_fpu->fpregs_active != old_fpu->fpstate_active);
+
+	if (old_fpu->fpstate_active) {
 		if (!copy_fpregs_to_fpstate(old_fpu))
 			old_fpu->last_cpu = -1;
 		else

arch/x86/kernel/fpu/core.c

@@ -100,7 +100,7 @@ void __kernel_fpu_begin(void)
 
 	kernel_fpu_disable();
 
-	if (fpu->fpregs_active) {
+	if (fpu->fpstate_active) {
 		/*
 		 * Ignore return value -- we don't care if reg state
 		 * is clobbered.
@@ -116,7 +116,7 @@ void __kernel_fpu_end(void)
 {
 	struct fpu *fpu = &current->thread.fpu;
 
-	if (fpu->fpregs_active)
+	if (fpu->fpstate_active)
 		copy_kernel_to_fpregs(&fpu->state);
 
 	kernel_fpu_enable();
@@ -147,8 +147,10 @@ void fpu__save(struct fpu *fpu)
 	WARN_ON_FPU(fpu != &current->thread.fpu);
 
 	preempt_disable();
+	WARN_ON_FPU(fpu->fpstate_active != fpu->fpregs_active);
+
 	trace_x86_fpu_before_save(fpu);
-	if (fpu->fpregs_active) {
+	if (fpu->fpstate_active) {
 		if (!copy_fpregs_to_fpstate(fpu)) {
 			copy_kernel_to_fpregs(&fpu->state);
 		}
@@ -262,11 +264,12 @@ EXPORT_SYMBOL_GPL(fpu__activate_curr);
  */
 void fpu__activate_fpstate_read(struct fpu *fpu)
 {
+	WARN_ON_FPU(fpu->fpstate_active != fpu->fpregs_active);
 	/*
 	 * If fpregs are active (in the current CPU), then
 	 * copy them to the fpstate:
 	 */
-	if (fpu->fpregs_active) {
+	if (fpu->fpstate_active) {
 		fpu__save(fpu);
 	} else {
 		if (!fpu->fpstate_active) {
@@ -362,12 +365,13 @@ void fpu__current_fpstate_write_end(void)
 {
 	struct fpu *fpu = &current->thread.fpu;
 
+	WARN_ON_FPU(fpu->fpstate_active != fpu->fpregs_active);
 	/*
 	 * 'fpu' now has an updated copy of the state, but the
 	 * registers may still be out of date.  Update them with
 	 * an XRSTOR if they are active.
 	 */
-	if (fpu->fpregs_active)
+	if (fpu->fpstate_active)
 		copy_kernel_to_fpregs(&fpu->state);
 
 	/*
@@ -417,7 +421,7 @@ void fpu__drop(struct fpu *fpu)
 	if (fpu == &current->thread.fpu) {
 		WARN_ON_FPU(fpu->fpstate_active != fpu->fpregs_active);
 
-		if (fpu->fpregs_active) {
+		if (fpu->fpstate_active) {
 			/* Ignore delayed exceptions from user space */
 			asm volatile("1: fwait\n"
 				     "2:\n"

arch/x86/kernel/fpu/signal.c

@@ -171,7 +171,9 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
 			sizeof(struct user_i387_ia32_struct), NULL,
 			(struct _fpstate_32 __user *) buf) ? -1 : 1;
 
-	if (fpu->fpregs_active || using_compacted_format()) {
+	WARN_ON_FPU(fpu->fpstate_active != fpu->fpregs_active);
+
+	if (fpu->fpstate_active || using_compacted_format()) {
 		/* Save the live register state to the user directly. */
 		if (copy_fpregs_to_sigframe(buf_fx))
 			return -1;

arch/x86/mm/pkeys.c

@@ -18,7 +18,6 @@
 
 #include <asm/cpufeature.h>             /* boot_cpu_has, ...            */
 #include <asm/mmu_context.h>            /* vma_pkey()                   */
-#include <asm/fpu/internal.h>           /* fpregs_active()              */
 
 int __execute_only_pkey(struct mm_struct *mm)
 {
@@ -45,7 +44,7 @@ int __execute_only_pkey(struct mm_struct *mm)
 	 */
 	preempt_disable();
 	if (!need_to_set_mm_pkey &&
-	    current->thread.fpu.fpregs_active &&
+	    current->thread.fpu.fpstate_active &&
 	    !__pkru_allows_read(read_pkru(), execute_only_pkey)) {
 		preempt_enable();
 		return execute_only_pkey;