x86/xsaves: Add a kernel parameter noxsaves to disable xsaves/xrstors

This patch adds a kernel parameter noxsaves to disable xsaves/xrstors feature.
The kernel will fall back to use xsaveopt and xrstor to save and restor
xstates. By using this parameter, xsave area occupies more memory because
standard form of xsave area in xsaveopt/xrstor occupies more memory than
compacted form of xsave area.

This patch adds a description of the kernel parameter noxsaveopt in doc.
The code to support the parameter noxsaveopt has been in the kernel before.
This patch just adds the description of this parameter in the doc.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1401387164-43416-4-git-send-email-fenghua.yu@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index e7c4b979d504..cdc95852532d 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -146,6 +146,7 @@ static int __init x86_xsave_setup(char *s)
 {
         setup_clear_cpu_cap(X86_FEATURE_XSAVE);
         setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
+        setup_clear_cpu_cap(X86_FEATURE_XSAVES);
         setup_clear_cpu_cap(X86_FEATURE_AVX);
         setup_clear_cpu_cap(X86_FEATURE_AVX2);
         return 1;
@@ -159,6 +160,13 @@ static int __init x86_xsaveopt_setup(char *s)
 }
 __setup("noxsaveopt", x86_xsaveopt_setup);
 
+static int __init x86_xsaves_setup(char *s)
+{
+        setup_clear_cpu_cap(X86_FEATURE_XSAVES);
+        return 1;
+}
+__setup("noxsaves", x86_xsaves_setup);
+
 #ifdef CONFIG_X86_32
 static int cachesize_override = -1;
 static int disable_x86_serial_nr = 1;