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From:   Xin Li <xin3.li@intel.com>
To:     linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org
Cc:     tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, hpa@zytor.com, peterz@infradead.org,
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        ravi.v.shankar@intel.com
Subject: [RFC PATCH 09/32] x86/cpu: add X86_CR4_FRED macro
Date:   Mon, 19 Dec 2022 22:36:35 -0800
Message-Id: <20221220063658.19271-10-xin3.li@intel.com>
In-Reply-To: <20221220063658.19271-1-xin3.li@intel.com>
References: <20221220063658.19271-1-xin3.li@intel.com>
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From: "H. Peter Anvin (Intel)" <hpa@zytor.com>

Add X86_CR4_FRED macro for the FRED bit in %cr4. This bit should be a
pinned bit, not to be changed after initialization.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
---
 arch/x86/include/uapi/asm/processor-flags.h |  2 ++
 arch/x86/kernel/cpu/common.c                | 11 ++++++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/uapi/asm/processor-flags.h b/arch/x86/include/uapi/asm/processor-flags.h
index c47cc7f2feeb..a90933f1ff41 100644
--- a/arch/x86/include/uapi/asm/processor-flags.h
+++ b/arch/x86/include/uapi/asm/processor-flags.h
@@ -132,6 +132,8 @@
 #define X86_CR4_PKE		_BITUL(X86_CR4_PKE_BIT)
 #define X86_CR4_CET_BIT		23 /* enable Control-flow Enforcement Technology */
 #define X86_CR4_CET		_BITUL(X86_CR4_CET_BIT)
+#define X86_CR4_FRED_BIT	32 /* enable FRED kernel entry */
+#define X86_CR4_FRED		_BITULL(X86_CR4_FRED_BIT)
 
 /*
  * x86-64 Task Priority Register, CR8
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index d6eb4f60b47d..05a5538052ad 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -411,10 +411,15 @@ static __always_inline void setup_umip(struct cpuinfo_x86 *c)
 	cr4_clear_bits(X86_CR4_UMIP);
 }
 
-/* These bits should not change their value after CPU init is finished. */
+/*
+ * These bits should not change their value after CPU init is
+ * finished.  The explicit cast to unsigned long suppresses a warning
+ * on i386 for x86-64 only feature bits >= 32.
+ */
 static const unsigned long cr4_pinned_mask =
-	X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_UMIP |
-	X86_CR4_FSGSBASE | X86_CR4_CET;
+	(unsigned long)
+	(X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_UMIP |
+	 X86_CR4_FSGSBASE | X86_CR4_CET | X86_CR4_FRED);
 static DEFINE_STATIC_KEY_FALSE_RO(cr_pinning);
 static unsigned long cr4_pinned_bits __ro_after_init;
 
-- 
2.34.1