From: Ingo Molnar <mingo@kernel.org>
Date: Fri, 24 Apr 2015 09:43:47 +0000 (+0200)
Subject: x86/fpu: Explain the AVX register layout in the xsave area
X-Git-Tag: v4.2-rc1~170^2~165
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=e783e8167ddf275782ef448eb139fafff3ac3af2;p=karo-tx-linux.git

x86/fpu: Explain the AVX register layout in the xsave area

The previous explanation was rather cryptic.

Also transform "u32 [64]" to the more readable "u8[256]" form.

No change in implementation.

Reviewed-by: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index 9bd2cd1a19fd..8a5120a3b48b 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -78,9 +78,16 @@ struct i387_soft_struct {
 	u32			entry_eip;
 };
 
+/*
+ * There are 16x 256-bit AVX registers named YMM0-YMM15.
+ * The low 128 bits are aliased to the 16 SSE registers (XMM0-XMM15)
+ * and are stored in 'struct i387_fxsave_struct::xmm_space[]'.
+ *
+ * The high 128 bits are stored here:
+ *    16x 128 bits == 256 bytes.
+ */
 struct ymmh_struct {
-	/* 16 * 16 bytes for each YMMH-reg = 256 bytes */
-	u32				ymmh_space[64];
+	u8				ymmh_space[256];
 };
 
 /* We don't support LWP yet: */