linux-kernel - [PATCH v2 3/8] x86/fpu/xstate: Introduce XSAVES supervisor states

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Date:   Tue, 21 Jan 2020 12:18:38 -0800
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Rik van Riel <riel@...riel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH v2 3/8] x86/fpu/xstate: Introduce XSAVES supervisor states

Enable XSAVES supervisor states by setting MSR_IA32_XSS bits according to
CPUID enumeration results.  Also revise comments at various places.

v2:
- Remove printing of supervisor xstates from fpu__init_system_xstate().

Co-developed-by: Fenghua Yu <fenghua.yu@...el.com>
Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
---
 arch/x86/kernel/fpu/xstate.c | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 3b22d630f5bb..0c5c91ee235e 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -229,13 +229,14 @@ void fpu__init_cpu_xstate(void)
 	 * states can be set here.
 	 */
 	xsetbv(XCR_XFEATURE_ENABLED_MASK, xfeatures_mask_user());
+
+	/*
+	 * MSR_IA32_XSS sets supervisor states managed by XSAVES.
+	 */
+	if (boot_cpu_has(X86_FEATURE_XSAVES))
+		wrmsrl(MSR_IA32_XSS, xfeatures_mask_supervisor());
 }
 
-/*
- * Note that in the future we will likely need a pair of
- * functions here: one for user xstates and the other for
- * system xstates.  For now, they are the same.
- */
 static int xfeature_enabled(enum xfeature xfeature)
 {
 	return !!(xfeatures_mask_all & (1UL << xfeature));
@@ -626,9 +627,6 @@ static void do_extra_xstate_size_checks(void)
  * the size of the *user* states.  If we use it to size a buffer
  * that we use 'XSAVES' on, we could potentially overflow the
  * buffer because 'XSAVES' saves system states too.
- *
- * Note that we do not currently set any bits on IA32_XSS so
- * 'XCR0 | IA32_XSS == XCR0' for now.
  */
 static unsigned int __init get_xsaves_size(void)
 {
@@ -751,7 +749,11 @@ void __init fpu__init_system_xstate(void)
 	cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
 	xfeatures_mask_all = eax + ((u64)edx << 32);
 
-	/* Place supervisor features in xfeatures_mask_all here */
+	/*
+	 * Find supervisor xstates supported by the processor.
+	 */
+	cpuid_count(XSTATE_CPUID, 1, &eax, &ebx, &ecx, &edx);
+	xfeatures_mask_all |= ecx + ((u64)edx << 32);
 
 	if ((xfeatures_mask_user() & XFEATURE_MASK_FPSSE) != XFEATURE_MASK_FPSSE) {
 		/*
@@ -812,6 +814,13 @@ void fpu__resume_cpu(void)
 	 */
 	if (boot_cpu_has(X86_FEATURE_XSAVE))
 		xsetbv(XCR_XFEATURE_ENABLED_MASK, xfeatures_mask_user());
+
+	/*
+	 * Restore IA32_XSS. The same CPUID bit enumerates support
+	 * of XSAVES and MSR_IA32_XSS.
+	 */
+	if (boot_cpu_has(X86_FEATURE_XSAVES))
+		wrmsrl(MSR_IA32_XSS, xfeatures_mask_supervisor());
 }
 
 /*
-- 
2.21.0