x86/xsaves: Change compacted format xsave area header

The XSAVE area header is changed to support both compacted format and
standard format of xsave area.

The XSAVE header of an xsave area comprises the 64 bytes starting at offset
512 from the area base address:

- Bytes 7:0 of the xsave header is a state-component bitmap called
  xstate_bv. It identifies the state components in the xsave area.

- Bytes 15:8 of the xsave header is a state-component bitmap called
  xcomp_bv. It is used as follows:
  - xcomp_bv[63] indicates the format of the extended region of
    the xsave area. If it is clear, the standard format is used.
    If it is set, the compacted format is used.
  - xcomp_bv[62:0] indicate which features (starting at feature 2)
    have space allocated for them in the compacted format.

- Bytes 63:16 of the xsave header are reserved.

Signed-off-by: Fenghua Yu <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: H. Peter Anvin <[email protected]>

Author: Fenghua Yu

arch/x86/include/asm/processor.h

@@ -386,8 +386,8 @@ struct bndcsr_struct {
 
 struct xsave_hdr_struct {
 	u64 xstate_bv;
-	u64 reserved1[2];
-	u64 reserved2[5];
+	u64 xcomp_bv;
+	u64 reserved[6];
 } __attribute__((packed));
 
 struct xsave_struct {