linux-kernel - [PATCH 1/3] x86/fpu/xstate: Fix last_good_offset in setup_xstate

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Message-Id: <20200109211452.27369-2-yu-cheng.yu@intel.com>
Date:   Thu,  9 Jan 2020 13:14:50 -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 1/3] x86/fpu/xstate: Fix last_good_offset in setup_xstate_features()

The function setup_xstate_features() uses CPUID to find each xfeature's
standard-format offset and size.  Since XSAVES always uses the compacted
format, supervisor xstates are *NEVER* in the standard-format and their
offsets are left as -1's.  However, they are still being tracked as
last_good_offset.

Fix it by tracking only user xstate offsets.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>
---
 arch/x86/kernel/fpu/xstate.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index a1806598aaa4..3ef3603bcfc5 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -265,22 +265,26 @@ static void __init setup_xstate_features(void)
 
 		cpuid_count(XSTATE_CPUID, i, &eax, &ebx, &ecx, &edx);
 
+		xstate_sizes[i] = eax;
+
 		/*
 		 * If an xfeature is supervisor state, the offset
 		 * in EBX is invalid. We leave it to -1.
 		 */
-		if (xfeature_is_user(i))
+		if (xfeature_is_user(i)) {
 			xstate_offsets[i] = ebx;
 
-		xstate_sizes[i] = eax;
-		/*
-		 * In our xstate size checks, we assume that the
-		 * highest-numbered xstate feature has the
-		 * highest offset in the buffer.  Ensure it does.
-		 */
-		WARN_ONCE(last_good_offset > xstate_offsets[i],
-			"x86/fpu: misordered xstate at %d\n", last_good_offset);
-		last_good_offset = xstate_offsets[i];
+			/*
+			 * In our xstate size checks, we assume that the
+			 * highest-numbered xstate feature has the
+			 * highest offset in the buffer.  Ensure it does.
+			 */
+			WARN_ONCE(last_good_offset > xstate_offsets[i],
+				"x86/fpu: misordered xstate at %d\n",
+				last_good_offset);
+
+			last_good_offset = xstate_offsets[i];
+		}
 	}
 }
 
-- 
2.21.0