Define kernel API to get address of each state in xsave area

In standard form, each state is saved in the xsave area in fixed offset.
But in compacted form, offset of each saved state only can be calculated during
run time because some xstates may not be enabled and saved.

We define kernel API get_xsave_addr() returns address of a given state saved in a xsave area.

It can be called in kernel to get address of each xstate in xsave area in
either standard format or compacted format.

It's useful when kernel wants to directly access each state in xsave area.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1401387164-43416-17-git-send-email-fenghua.yu@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/include/asm/xsave.h

@@ -255,4 +255,7 @@ static inline int xrestore_user(struct xsave_struct __user *buf, u64 mask)
 	return err;
 }
 
+void *get_xsave_addr(struct xsave_struct *xsave, int xstate);
+void setup_xstate_comp(void);
+
 #endif

arch/x86/kernel/process.c

@@ -93,6 +93,7 @@ void arch_task_cache_init(void)
         	kmem_cache_create("task_xstate", xstate_size,
 				  __alignof__(union thread_xstate),
 				  SLAB_PANIC | SLAB_NOTRACK, NULL);
+	setup_xstate_comp();
 }
 
 /*

arch/x86/kernel/xsave.c

@@ -481,6 +481,47 @@ static void __init setup_xstate_features(void)
 	} while (1);
 }
 
+/*
+ * This function sets up offsets and sizes of all extended states in
+ * xsave area. This supports both standard format and compacted format
+ * of the xsave aread.
+ *
+ * Input: void
+ * Output: void
+ */
+void setup_xstate_comp(void)
+{
+	int i;
+
+	xstate_comp_offsets = kmalloc(xstate_features * sizeof(int),
+				      GFP_KERNEL);
+	xstate_comp_sizes = kmalloc(xstate_features * sizeof(int), GFP_KERNEL);
+
+	if (!cpu_has_xsaves) {
+		for (i = 2; i < xstate_features; i++) {
+			if (test_bit(i, (unsigned long *)&pcntxt_mask)) {
+				xstate_comp_offsets[i] = xstate_offsets[i];
+				xstate_comp_sizes[i] = xstate_sizes[i];
+			}
+		}
+		return;
+	}
+
+	xstate_comp_offsets[2] = FXSAVE_SIZE + XSAVE_HDR_SIZE;
+
+	for (i = 2; i < xstate_features; i++) {
+		if (test_bit(i, (unsigned long *)&pcntxt_mask))
+			xstate_comp_sizes[i] = xstate_sizes[i];
+		else
+			xstate_comp_sizes[i] = 0;
+
+		if (i > 2)
+			xstate_comp_offsets[i] = xstate_comp_offsets[i-1]
+					+ xstate_comp_sizes[i-1];
+
+	}
+}
+
 /*
  * setup the xstate image representing the init state
  */
@@ -668,3 +709,26 @@ void eager_fpu_init(void)
 	else
 		fxrstor_checking(&init_xstate_buf->i387);
 }
+
+/*
+ * Given the xsave area and a state inside, this function returns the
+ * address of the state.
+ *
+ * This is the API that is called to get xstate address in either
+ * standard format or compacted format of xsave area.
+ *
+ * Inputs:
+ *	xsave: base address of the xsave area;
+ *	xstate: state which is defined in xsave.h (e.g. XSTATE_FP, XSTATE_SSE,
+ *	etc.)
+ * Output:
+ *	address of the state in the xsave area.
+ */
+void *get_xsave_addr(struct xsave_struct *xsave, int xstate)
+{
+	int feature = fls64(xstate) - 1;
+	if (!test_bit(feature, (unsigned long *)&pcntxt_mask))
+		return NULL;
+
+	return (void *)xsave + xstate_comp_offsets[feature];
+}