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Subject[PATCH 24/27] x86/fpu: Add a fastpath to __fpu__restore_sig()
Date
The previous commits refactor the restoration of the FPU registers so
that they can be loaded from in-kernel memory. This overhead can be
avoided if the load can be performed without a pagefault.

Attempt to restore FPU registers by invoking
copy_user_to_fpregs_zeroing(). If it fails try the slowpath which can handle
pagefaults.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
arch/x86/kernel/fpu/signal.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index a5b086ec426a5..f20e1d1fffa29 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -242,10 +242,10 @@ sanitize_restored_xstate(union fpregs_state *state,
/*
* Restore the extended state if present. Otherwise, restore the FP/SSE state.
*/
-static inline int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only)
+static int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only)
{
if (use_xsave()) {
- if ((unsigned long)buf % 64 || fx_only) {
+ if (fx_only) {
u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE;
copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
return copy_user_to_fxregs(buf);
@@ -327,7 +327,19 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
if (ret)
goto err_out;
envp = &env;
+ } else {
+ fpregs_lock();
+ pagefault_disable();
+ ret = copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only);
+ pagefault_enable();
+ if (!ret) {
+ fpregs_mark_activate();
+ fpregs_unlock();
+ return 0;
+ }
+ fpregs_unlock();
}
+
if (use_xsave() && !fx_only) {
u64 init_bv = xfeatures_mask & ~xfeatures;

--
2.20.1
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