x86, xsave: context switch support using xsave/xrstor

Uses xsave/xrstor (instead of traditional fxsave/fxrstor) in context switch
when available.

Introduces TS_XSAVE flag, which determine the need to use xsave/xrstor
instructions during context switch instead of the legacy fxsave/fxrstor
instructions. Thread-synchronous status word is already in L1 cache during
this code patch and thus minimizes the performance penality compared to
(cpu_has_xsave) checks.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 34 insertions, 1 deletions

diff --git a/include/asm-x86/xsave.h b/include/asm-x86/xsave.h
index 6d70e62c6bdc..e835a917ee19 100644
--- a/include/asm-x86/xsave.h
+++ b/include/asm-x86/xsave.h
@@ -17,10 +17,43 @@
 #define XCNTXT_LMASK    (XSTATE_FP | XSTATE_SSE)
 #define XCNTXT_HMASK    0x0
 
+#ifdef CONFIG_X86_64
+#define REX_PREFIX      "0x48, "
+#else
+#define REX_PREFIX
+#endif
+
 extern unsigned int xstate_size, pcntxt_hmask, pcntxt_lmask;
 extern struct xsave_struct *init_xstate_buf;
 
 extern void xsave_cntxt_init(void);
 extern void xsave_init(void);
-
+extern int init_fpu(struct task_struct *child);
+
+static inline int xrstor_checking(struct xsave_struct *fx)
+{
+        int err;
+
+        asm volatile("1: .byte " REX_PREFIX "0x0f,0xae,0x2f\n\t"
+                     "2:\n"
+                     ".section .fixup,\"ax\"\n"
+                     "3:  movl $-1,%[err]\n"
+                     "    jmp  2b\n"
+                     ".previous\n"
+                     _ASM_EXTABLE(1b, 3b)
+                     : [err] "=r" (err)
+                     : "D" (fx), "m" (*fx), "a" (-1), "d" (-1), "0" (0)
+                     : "memory");
+
+        return err;
+}
+
+static inline void xsave(struct task_struct *tsk)
+{
+        /* This, however, we can work around by forcing the compiler to select
+           an addressing mode that doesn't require extended registers. */
+        __asm__ __volatile__(".byte " REX_PREFIX "0x0f,0xae,0x27"
+                             : : "D" (&(tsk->thread.xstate->xsave)),
+                                 "a" (-1), "d"(-1) : "memory");
+}
 #endif