linux-kernel - [PATCH v4 10/10] x86/xsaves: Re-enable XSAVES

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Message-Id: <fa1efcfe34e0953385377d567d28bb2ef13fd3c6.1457038929.git.yu-cheng.yu@intel.com>
Date:	Fri,  4 Mar 2016 10:12:39 -0800
From:	Yu-cheng Yu <yu-cheng.yu@...el.com>
To:	x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Cc:	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...e.de>,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
	"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH v4 10/10] x86/xsaves: 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@...el.com>
---
 arch/x86/kernel/fpu/init.c   | 15 ---------------
 arch/x86/kernel/fpu/xstate.c | 10 ++++++++++
 2 files changed, 10 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index b5952d5..6bfa059 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -226,21 +226,6 @@ static void __init fpu__init_system_xstate_size_legacy(void)
 	}
 
 	user_xstate_size = 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 06618ea..541f56e 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -204,6 +204,16 @@ void fpu__init_cpu_xstate(void)
 	if (!cpu_has_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);
 }
-- 
1.9.1