[PATCH 05/22 v2] x86/fpu: Remove fpu->initialized usage in copy_fpstate_to_sigframe()

Sebastian Andrzej Siewior
2019-02-05T14:37:10Z

With lazy-FPU support the (now named variable) ->initialized was set to true if
the CPU's FPU registers were holding the a valid state of the FPU registers for
the active process. If it was set to false then the FPU state was saved in
fpu->state and the FPU was deactivated.
With lazy-FPU gone, ->initialized is always true for user threads and kernel
threads never this function so ->initialized is always true in
copy_fpstate_to_sigframe().
The using_compacted_format() check is also a leftover from the lazy-FPU time.
In the `->initialized == false' case copy_to_user() would copy the compacted
buffer while userland would expect the non-compacted format instead. So in
order to save the FPU state in the non-compacted form it issues the xsave
opcode to save the *current* FPU state.
The FPU is not enabled so the attempt raises the FPU trap, the trap restores
the FPU content and re-enables the FPU and the xsave opcode is invoked again and
succeeds. *This* does not longer work since commit

bef8b6da9522 ("x86/fpu: Handle #NM without FPU emulation as an error")

Remove check for ->initialized because it is always true and remove the
false condition. Update the comment to reflect that the "state is always live".

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
v1…v2: rewrite the patch description.

arch/x86/kernel/fpu/signal.c | 30 ++++++------------------------
1 file changed, 6 insertions(+), 24 deletions(-)

Index: staging/arch/x86/kernel/fpu/signal.c
===================================================================
--- staging.orig/arch/x86/kernel/fpu/signal.c
+++ staging/arch/x86/kernel/fpu/signal.c
@@ -144,9 +144,8 @@ static inline int copy_fpregs_to_sigfram
* buf == buf_fx for 64-bit frames and 32-bit fsave frame.
* buf != buf_fx for 32-bit frames with fxstate.
*
- * If the fpu, extended register state is live, save the state directly
- * to the user frame pointed by the aligned pointer 'buf_fx'. Otherwise,
- * copy the thread's fpu state to the user frame starting at 'buf_fx'.
+ * Save the state directly to the user frame pointed by the aligned pointer
+ * 'buf_fx'.
*
* If this is a 32-bit frame with fxstate, put a fsave header before
* the aligned state at 'buf_fx'.
@@ -157,7 +156,6 @@ static inline int copy_fpregs_to_sigfram
int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
{
struct fpu *fpu = &current->thread.fpu;
- struct xregs_state *xsave = &fpu->state.xsave;
struct task_struct *tsk = current;
int ia32_fxstate = (buf != buf_fx);

@@ -172,29 +170,12 @@ int copy_fpstate_to_sigframe(void __user
sizeof(struct user_i387_ia32_struct), NULL,
(struct _fpstate_32 __user *) buf) ? -1 : 1;

- if (fpu->initialized || using_compacted_format()) {
- /* Save the live register state to the user directly. */
- if (copy_fpregs_to_sigframe(buf_fx))
- return -1;
- /* Update the thread's fxstate to save the fsave header. */
- if (ia32_fxstate)
- copy_fxregs_to_kernel(fpu);
- } else {
- /*
- * It is a *bug* if kernel uses compacted-format for xsave
- * area and we copy it out directly to a signal frame. It
- * should have been handled above by saving the registers
- * directly.
- */
- if (boot_cpu_has(X86_FEATURE_XSAVES)) {
- WARN_ONCE(1, "x86/fpu: saving compacted-format xsave area to a signal frame!\n");
- return -1;
- }
-
- fpstate_sanitize_xstate(fpu);
- if (__copy_to_user(buf_fx, xsave, fpu_user_xstate_size))
- return -1;
- }
+ /* Save the live register state to the user directly. */
+ if (copy_fpregs_to_sigframe(buf_fx))
+ return -1;
+ /* Update the thread's fxstate to save the fsave header. */
+ if (ia32_fxstate)
+ copy_fxregs_to_kernel(fpu);

/* Save the fsave header for the 32-bit frames. */
if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf))