Re: [PATCH v10 13/38] x86/cpu: Add X86_CR4_FRED macro

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On 14.09.23 г. 7:47 ч., Xin Li wrote:
From: "H. Peter Anvin (Intel)" <hpa@xxxxxxxxx>

Add X86_CR4_FRED macro for the FRED bit in %cr4. This bit must not be
changed after initialization, so add it to the pinned CR4 bits.

Signed-off-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
Tested-by: Shan Kang <shan.kang@xxxxxxxxx>
Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>
---

Changes since v9:
* Avoid a type cast by defining X86_CR4_FRED as 0 on 32-bit (Thomas
   Gleixner).
---
  arch/x86/include/uapi/asm/processor-flags.h | 7 +++++++
  arch/x86/kernel/cpu/common.c                | 5 ++---
  2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/uapi/asm/processor-flags.h b/arch/x86/include/uapi/asm/processor-flags.h
index d898432947ff..f1a4adc78272 100644
--- a/arch/x86/include/uapi/asm/processor-flags.h
+++ b/arch/x86/include/uapi/asm/processor-flags.h
@@ -139,6 +139,13 @@
  #define X86_CR4_LAM_SUP_BIT	28 /* LAM for supervisor pointers */
  #define X86_CR4_LAM_SUP		_BITUL(X86_CR4_LAM_SUP_BIT)
+#ifdef __x86_64__
+#define X86_CR4_FRED_BIT	32 /* enable FRED kernel entry */
+#define X86_CR4_FRED		_BITUL(X86_CR4_FRED_BIT)

nit: s/BITUL/BITULL I guess if __x86_64__ is defined then we are guaranteed that unsigned long will be a 64 bit, but for the sake of clarity I'd rather have this spelled out explicitly by using BITULL


+#else
+#define X86_CR4_FRED		(0)
+#endif
+
  /*
   * x86-64 Task Priority Register, CR8
   */
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 317b4877e9c7..42511209469b 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -400,9 +400,8 @@ static __always_inline void setup_umip(struct cpuinfo_x86 *c)
  }
/* These bits should not change their value after CPU init is finished. */
-static const unsigned long cr4_pinned_mask =
-	X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_UMIP |
-	X86_CR4_FSGSBASE | X86_CR4_CET;
+static const unsigned long cr4_pinned_mask = 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;



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