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Subject[tip:x86/fpu] x86/fpu/xstate: Re-enable XSAVES
Commit-ID:  b8be15d588060a03569ac85dc4a0247460988f5b
Gitweb: http://git.kernel.org/tip/b8be15d588060a03569ac85dc4a0247460988f5b
Author: Yu-cheng Yu <yu-cheng.yu@intel.com>
AuthorDate: Mon, 11 Jul 2016 09:18:57 -0700
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 11 Jul 2016 16:44:01 +0200

x86/fpu/xstate: Re-enable XSAVES

We did not handle XSAVES instructions correctly. There were issues in
converting between standard and compacted format when interfacing with
user-space. These issues have been corrected.

Add a WARN_ONCE() to make it clear that XSAVES supervisor states are not
yet implemented.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Cc: H. Peter Anvin <h.peter.anvin@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi V Shankar <ravi.v.shankar@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1468253937-40008-5-git-send-email-fenghua.yu@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/kernel/fpu/init.c | 15 ---------------
arch/x86/kernel/fpu/xstate.c | 9 +++++++++
2 files changed, 9 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 60f3839..93982ae 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -230,21 +230,6 @@ static void __init fpu__init_system_xstate_size_legacy(void)
}

fpu_user_xstate_size = fpu_kernel_xstate_size;
-
- /*
- * Quirk: we don't yet handle the XSAVES* instructions
- * correctly, as we don't correctly convert between
- * standard and compacted format when interfacing
- * with user-space - so disable it for now.
- *
- * The difference is small: with recent CPUs the
- * compacted format is only marginally smaller than
- * the standard FPU state format.
- *
- * ( This is easy to backport while we are fixing
- * XSAVES* support. )
- */
- setup_clear_cpu_cap(X86_FEATURE_XSAVES);
}

/*
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 4fb8dd7..3169bca 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -221,6 +221,15 @@ void fpu__init_cpu_xstate(void)
{
if (!boot_cpu_has(X86_FEATURE_XSAVE) || !xfeatures_mask)
return;
+ /*
+ * Make it clear that XSAVES supervisor states are not yet
+ * implemented should anyone expect it to work by changing
+ * bits in XFEATURE_MASK_* macros and XCR0.
+ */
+ WARN_ONCE((xfeatures_mask & XFEATURE_MASK_SUPERVISOR),
+ "x86/fpu: XSAVES supervisor states are not yet implemented.\n");
+
+ xfeatures_mask &= ~XFEATURE_MASK_SUPERVISOR;

cr4_set_bits(X86_CR4_OSXSAVE);
xsetbv(XCR_XFEATURE_ENABLED_MASK, xfeatures_mask);
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