x86, xsave: enable xsave/xrstor on cpus with xsave support

Enables xsave/xrstor by turning on cr4.osxsave on cpu's which have
the xsave support. For now, features that OS supports/enabled are
FP and SSE.

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>

arch/x86/kernel/xsave.c

@@ -0,0 +1,87 @@
+/*
+ * xsave/xrstor support.
+ *
+ * Author: Suresh Siddha <suresh.b.siddha@intel.com>
+ */
+#include <linux/bootmem.h>
+#include <linux/compat.h>
+#include <asm/i387.h>
+
+/*
+ * Supported feature mask by the CPU and the kernel.
+ */
+unsigned int pcntxt_hmask, pcntxt_lmask;
+
+/*
+ * Represents init state for the supported extended state.
+ */
+struct xsave_struct *init_xstate_buf;
+
+/*
+ * Enable the extended processor state save/restore feature
+ */
+void __cpuinit xsave_init(void)
+{
+	if (!cpu_has_xsave)
+		return;
+
+	set_in_cr4(X86_CR4_OSXSAVE);
+
+	/*
+	 * Enable all the features that the HW is capable of
+	 * and the Linux kernel is aware of.
+	 *
+	 * xsetbv();
+	 */
+	asm volatile(".byte 0x0f,0x01,0xd1" : : "c" (0),
+		     "a" (pcntxt_lmask), "d" (pcntxt_hmask));
+}
+
+/*
+ * setup the xstate image representing the init state
+ */
+void setup_xstate_init(void)
+{
+	init_xstate_buf = alloc_bootmem(xstate_size);
+	init_xstate_buf->i387.mxcsr = MXCSR_DEFAULT;
+}
+
+/*
+ * Enable and initialize the xsave feature.
+ */
+void __init xsave_cntxt_init(void)
+{
+	unsigned int eax, ebx, ecx, edx;
+
+	cpuid_count(0xd, 0, &eax, &ebx, &ecx, &edx);
+
+	pcntxt_lmask = eax;
+	pcntxt_hmask = edx;
+
+	if ((pcntxt_lmask & XSTATE_FPSSE) != XSTATE_FPSSE) {
+		printk(KERN_ERR "FP/SSE not shown under xsave features %x\n",
+		       pcntxt_lmask);
+		BUG();
+	}
+
+	/*
+	 * for now OS knows only about FP/SSE
+	 */
+	pcntxt_lmask = pcntxt_lmask & XCNTXT_LMASK;
+	pcntxt_hmask = pcntxt_hmask & XCNTXT_HMASK;
+
+	xsave_init();
+
+	/*
+	 * Recompute the context size for enabled features
+	 */
+	cpuid_count(0xd, 0, &eax, &ebx, &ecx, &edx);
+
+	xstate_size = ebx;
+
+	setup_xstate_init();
+
+	printk(KERN_INFO "xsave/xrstor: enabled xstate_bv 0x%Lx, "
+	       "cntxt size 0x%x\n",
+	       (pcntxt_lmask | ((u64) pcntxt_hmask << 32)), xstate_size);
+}