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Subject[patch V3 63/66] x86/fpu/signal: Split out the direct restore code
Prepare for smarter failure handling of the direct restore.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/kernel/fpu/signal.c | 110 +++++++++++++++++++++----------------------
1 file changed, 56 insertions(+), 54 deletions(-)

--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -249,10 +249,7 @@ sanitize_restored_user_xstate(union fpre
}
}

-/*
- * Restore the FPU state directly from the userspace signal frame.
- */
-static int restore_fpregs_from_user(void __user *buf, u64 xrestore, bool fx_only)
+static int restore_hwregs_from_user(void __user *buf, u64 xrestore, bool fx_only)
{
if (use_xsave()) {
u64 init_bv = xfeatures_mask_uabi() & ~xrestore;
@@ -273,6 +270,56 @@ static int restore_fpregs_from_user(void
}
}

+static int restore_fpregs_from_user(void __user *buf, u64 xrestore, bool fx_only)
+{
+ struct fpu *fpu = &current->thread.fpu;
+ int ret ;
+
+ fpregs_lock();
+ pagefault_disable();
+ ret = restore_hwregs_from_user(buf, xrestore, fx_only);
+ pagefault_enable();
+
+ if (unlikely(ret)) {
+ /*
+ * The above did an FPU restore operation, restricted to
+ * the user portion of the registers, and failed, but the
+ * microcode might have modified the FPU registers
+ * nevertheless.
+ *
+ * If the FPU registers do not belong to current, then
+ * invalidate the FPU register state otherwise the task
+ * might preempt current and return to user space with
+ * corrupted FPU registers.
+ *
+ * In case current owns the FPU registers then no further
+ * action is required. The fixup in the slow path will
+ * handle it correctly.
+ */
+ if (test_thread_flag(TIF_NEED_FPU_LOAD))
+ __cpu_invalidate_fpregs_state();
+ fpregs_unlock();
+ return ret;
+ }
+
+ /*
+ * Restore supervisor states: previous context switch etc has done
+ * XSAVES and saved the supervisor states in the kernel buffer from
+ * which they can be restored now.
+ *
+ * We cannot do a single XRSTORS here - which would be nice -
+ * because the rest of the FPU registers are being restored from a
+ * user buffer directly. The single XRSTORS happens below, when the
+ * user buffer has been copied to the kernel one.
+ */
+ if (test_thread_flag(TIF_NEED_FPU_LOAD) && xfeatures_mask_supervisor())
+ os_xrstor(&fpu->state.xsave, xfeatures_mask_supervisor());
+
+ fpregs_mark_activate();
+ fpregs_unlock();
+ return 0;
+}
+
static int __fpu_restore_sig(void __user *buf, void __user *buf_fx,
bool ia32_fxstate)
{
@@ -297,61 +344,16 @@ static int __fpu_restore_sig(void __user
user_xfeatures = fx_sw_user.xfeatures;
}

- if (!ia32_fxstate) {
+ if (likely(!ia32_fxstate)) {
/*
* Attempt to restore the FPU registers directly from user
- * memory. For that to succeed, the user access cannot cause
- * page faults. If it does, fall back to the slow path below,
- * going through the kernel buffer with the enabled pagefault
- * handler.
+ * memory. For that to succeed, the user access cannot cause page
+ * faults. If it does, fall back to the slow path below, going
+ * through the kernel buffer with the enabled pagefault handler.
*/
- fpregs_lock();
- pagefault_disable();
ret = restore_fpregs_from_user(buf_fx, user_xfeatures, fx_only);
- pagefault_enable();
- if (!ret) {
-
- /*
- * Restore supervisor states: previous context switch
- * etc has done XSAVES and saved the supervisor states
- * in the kernel buffer from which they can be restored
- * now.
- *
- * We cannot do a single XRSTORS here - which would
- * be nice - because the rest of the FPU registers are
- * being restored from a user buffer directly. The
- * single XRSTORS happens below, when the user buffer
- * has been copied to the kernel one.
- */
- if (test_thread_flag(TIF_NEED_FPU_LOAD) &&
- xfeatures_mask_supervisor()) {
- os_xrstor(&fpu->state.xsave,
- xfeatures_mask_supervisor());
- }
- fpregs_mark_activate();
- fpregs_unlock();
+ if (likely(!ret))
return 0;
- }
-
- /*
- * The above did an FPU restore operation, restricted to
- * the user portion of the registers, and failed, but the
- * microcode might have modified the FPU registers
- * nevertheless.
- *
- * If the FPU registers do not belong to current, then
- * invalidate the FPU register state otherwise the task might
- * preempt current and return to user space with corrupted
- * FPU registers.
- *
- * In case current owns the FPU registers then no further
- * action is required. The fixup below will handle it
- * correctly.
- */
- if (test_thread_flag(TIF_NEED_FPU_LOAD))
- __cpu_invalidate_fpregs_state();
-
- fpregs_unlock();
} else {
/*
* For 32-bit frames with fxstate, copy the fxstate so it can
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