x86/fpu: Move fpu__write_begin() to regset

The only usecase for fpu__write_begin is the set() callback of regset, so
the function is pointlessly global.

Move it to the regset code and rename it to fpu_force_restore() which is
exactly decribing what the function does.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121453.328652975@linutronix.de

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 4c669f3..854bfb0 100644 (file)
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -26,7 +26,6 @@
 /*
  * High level FPU state handling functions:
  */
-extern void fpu__prepare_write(struct fpu *fpu);
 extern void fpu__save(struct fpu *fpu);
 extern int  fpu__restore_sig(void __user *buf, int ia32_frame);
 extern void fpu__drop(struct fpu *fpu);

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index d390644..2243701 100644 (file)
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -281,30 +281,6 @@ static void fpu__initialize(struct fpu *fpu)
        trace_x86_fpu_init_state(fpu);
 }
 
-/*
- * This function must be called before we write a task's fpstate.
- *
- * Invalidate any cached FPU registers.
- *
- * After this function call, after registers in the fpstate are
- * modified and the child task has woken up, the child task will
- * restore the modified FPU state from the modified context. If we
- * didn't clear its cached status here then the cached in-registers
- * state pending on its former CPU could be restored, corrupting
- * the modifications.
- */
-void fpu__prepare_write(struct fpu *fpu)
-{
-       /*
-        * Only stopped child tasks can be used to modify the FPU
-        * state in the fpstate buffer:
-        */
-       WARN_ON_FPU(fpu == &current->thread.fpu);
-
-       /* Invalidate any cached state: */
-       __fpu_invalidate_fpregs_state(fpu);
-}
-
 /*
  * Drops current FPU state: deactivates the fpregs and
  * the fpstate. NOTE: it still leaves previous contents

diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
index 937adf7..ddc290d 100644 (file)
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -44,6 +44,25 @@ static void sync_fpstate(struct fpu *fpu)
                fpu__save(fpu);
 }
 
+/*
+ * Invalidate cached FPU registers before modifying the stopped target
+ * task's fpstate.
+ *
+ * This forces the target task on resume to restore the FPU registers from
+ * modified fpstate. Otherwise the task might skip the restore and operate
+ * with the cached FPU registers which discards the modifications.
+ */
+static void fpu_force_restore(struct fpu *fpu)
+{
+       /*
+        * Only stopped child tasks can be used to modify the FPU
+        * state in the fpstate buffer:
+        */
+       WARN_ON_FPU(fpu == &current->thread.fpu);
+
+       __fpu_invalidate_fpregs_state(fpu);
+}
+
 int xfpregs_get(struct task_struct *target, const struct user_regset *regset,
                struct membuf to)
 {
@@ -88,7 +107,7 @@ int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
        if (newstate.mxcsr & ~mxcsr_feature_mask)
                return -EINVAL;
 
-       fpu__prepare_write(fpu);
+       fpu_force_restore(fpu);
 
        /* Copy the state  */
        memcpy(&fpu->state.fxsave, &newstate, sizeof(newstate));
@@ -146,7 +165,7 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
                }
        }
 
-       fpu__prepare_write(fpu);
+       fpu_force_restore(fpu);
        ret = copy_kernel_to_xstate(&fpu->state.xsave, kbuf ?: tmpbuf);
 
 out:
@@ -346,7 +365,7 @@ int fpregs_set(struct task_struct *target, const struct user_regset *regset,
        if (ret)
                return ret;
 
-       fpu__prepare_write(fpu);
+       fpu_force_restore(fpu);
 
        if (cpu_feature_enabled(X86_FEATURE_FXSR))
                convert_to_fxsr(&fpu->state.fxsave, &env);