[patch V3 22/66] x86/fpu: Move fpu__write_begin() to regset

From: Thomas Gleixner
Date: Fri Jun 18 2021 - 11:21:02 EST


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@xxxxxxxxxxxxx>
---
arch/x86/include/asm/fpu/internal.h | 1 -
arch/x86/kernel/fpu/core.c | 24 ------------------------
arch/x86/kernel/fpu/regset.c | 25 ++++++++++++++++++++++---
3 files changed, 22 insertions(+), 28 deletions(-)

--- 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);
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -282,30 +282,6 @@ static void fpu__initialize(struct 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
* in the fpregs in the eager-FPU case.
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -44,6 +44,25 @@ static void fpu_sync_fpstate(struct 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)
{
@@ -89,7 +108,7 @@ int xfpregs_set(struct task_struct *targ
if (newstate.mxcsr & ~mxcsr_feature_mask)
ret = -EINVAL;

- fpu__prepare_write(fpu);
+ fpu_force_restore(fpu);

/* Copy the state */
memcpy(&fpu->state.fxsave, &newstate, sizeof(newstate));
@@ -147,7 +166,7 @@ int xstateregs_set(struct task_struct *t
}
}

- fpu__prepare_write(fpu);
+ fpu_force_restore(fpu);
ret = copy_kernel_to_xstate(&fpu->state.xsave, kbuf ?: tmpbuf);

out:
@@ -347,7 +366,7 @@ int fpregs_set(struct task_struct *targe
if (ret)
return ret;

- fpu__prepare_write(fpu);
+ fpu_force_restore(fpu);

if (cpu_feature_enabled(X86_FEATURE_FXSR))
convert_to_fxsr(&target->thread.fpu.state.fxsave, &env);