linux-kernel - [PATCH v2 1/3] x86/fpu/xstate: Fix small issues before adding supervisor xstates

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Date:   Thu, 12 Dec 2019 13:08:53 -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 1/3] x86/fpu/xstate: Fix small issues before adding supervisor xstates

In response to earlier comments, fix small issues before introducing XSAVES
supervisor states:
- Fix comments of xfeature_is_supervisor().
- Replace ((u64)1 << 63) with XCOMP_BV_COMPACTED_FORMAT.

No functional changes from this patch.

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 | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 319be936c348..0bd313351650 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -110,12 +110,9 @@ EXPORT_SYMBOL_GPL(cpu_has_xfeatures);
 static int xfeature_is_supervisor(int xfeature_nr)
 {
 	/*
-	 * We currently do not support supervisor states, but if
-	 * we did, we could find out like this.
-	 *
-	 * SDM says: If state component 'i' is a user state component,
-	 * ECX[0] return 0; if state component i is a supervisor
-	 * state component, ECX[0] returns 1.
+	 * Extended State Enumeration Sub-leaves (EAX = 0DH, ECX = n, n > 1)
+	 * returns ECX[0] set to (1) for a supervisor state, and cleared (0)
+	 * for a user state.
 	 */
 	u32 eax, ebx, ecx, edx;
 
@@ -419,7 +416,8 @@ static void __init setup_init_fpu_buf(void)
 	print_xstate_features();
 
 	if (boot_cpu_has(X86_FEATURE_XSAVES))
-		init_fpstate.xsave.header.xcomp_bv = (u64)1 << 63 | xfeatures_mask;
+		init_fpstate.xsave.header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT |
+						     xfeatures_mask;
 
 	/*
 	 * Init all the features state with header.xfeatures being 0x0
-- 
2.17.1