[patch V3 40/66] x86/fpu: Rename and sanitize fpu__save/copy()

From: Thomas Gleixner
Date: Fri Jun 18 2021 - 11:24:49 EST


Both functions are misnomed.

fpu__save() is actually about synchronizing the hardware register state
into the task's memory state so that either coredump or a math exception
handler can inspect the state at the time where the problem happens.

The function guarantees to preserve the register state, while "save" is a
common terminology for saving the current state so it can be modified and
restored later. This is clearly not the case here.

Rename it to fpu_sync_fpstate().

fpu__copy() is used to clone the current task's FPU state when duplicating
task_struct. While the register state is a copy the rest of the FPU state
is not.

Name it accordingly and remove the really pointless @src argument along
with the warning which comes along with it.

Nothing can ever copy the FPU state of a non-current task. It's clearly
just a consequence of arch_dup_task_struct(), but it makes no sense to
proliferate that further.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
V3: New patch
---
arch/x86/include/asm/fpu/internal.h | 6 ++++--
arch/x86/kernel/fpu/core.c | 15 +++++++--------
arch/x86/kernel/fpu/regset.c | 2 +-
arch/x86/kernel/process.c | 3 +--
arch/x86/kernel/traps.c | 5 +++--
5 files changed, 16 insertions(+), 15 deletions(-)

--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -26,14 +26,16 @@
/*
* High level FPU state handling functions:
*/
-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);
-extern int fpu__copy(struct task_struct *dst, struct task_struct *src);
extern void fpu__clear_user_states(struct fpu *fpu);
extern void fpu__clear_all(struct fpu *fpu);
extern int fpu__exception_code(struct fpu *fpu, int trap_nr);

+extern void fpu_sync_fpstate(struct fpu *fpu);
+
+extern int fpu_clone(struct task_struct *dst);
+
/*
* Boot time FPU initialization functions:
*/
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -159,11 +159,10 @@ void kernel_fpu_end(void)
EXPORT_SYMBOL_GPL(kernel_fpu_end);

/*
- * Save the FPU state (mark it for reload if necessary):
- *
- * This only ever gets called for the current task.
+ * Sync the FPU register state to current's memory register state when the
+ * current task owns the FPU. The hardware register state is preserved.
*/
-void fpu__save(struct fpu *fpu)
+void fpu_sync_fpstate(struct fpu *fpu)
{
WARN_ON_FPU(fpu != &current->thread.fpu);

@@ -221,18 +220,18 @@ void fpstate_init(union fpregs_state *st
}
EXPORT_SYMBOL_GPL(fpstate_init);

-int fpu__copy(struct task_struct *dst, struct task_struct *src)
+/* Clone current's FPU state on fork */
+int fpu_clone(struct task_struct *dst)
{
+ struct fpu *src_fpu = &current->thread.fpu;
struct fpu *dst_fpu = &dst->thread.fpu;
- struct fpu *src_fpu = &src->thread.fpu;

+ /* The new task's FPU state cannot be valid in the hardware. */
dst_fpu->last_cpu = -1;

if (!static_cpu_has(X86_FEATURE_FPU))
return 0;

- WARN_ON_FPU(src_fpu != &current->thread.fpu);
-
/*
* Don't let 'init optimized' areas of the XSAVE area
* leak into the child task:
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -41,7 +41,7 @@ int regset_xregset_fpregs_active(struct
static void sync_fpstate(struct fpu *fpu)
{
if (fpu == &current->thread.fpu)
- fpu__save(fpu);
+ fpu_sync_fpstate(fpu);
}

/*
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -87,8 +87,7 @@ int arch_dup_task_struct(struct task_str
#ifdef CONFIG_VM86
dst->thread.vm86 = NULL;
#endif
-
- return fpu__copy(dst, src);
+ return fpu_clone(dst);
}

/*
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1046,9 +1046,10 @@ static void math_error(struct pt_regs *r
}

/*
- * Save the info for the exception handler and clear the error.
+ * Synchronize the FPU register state to the memory register state
+ * if necessary. This allows the exception handler to inspect it.
*/
- fpu__save(fpu);
+ fpu_sync_fpstate(fpu);

task->thread.trap_nr = trapnr;
task->thread.error_code = 0;