On 6/5/23 05:01, Thomas Gleixner wrote:
On Mon, Apr 10 2023 at 01:14, Xin Li wrote:
From: "H. Peter Anvin (Intel)" <hpa@xxxxxxxxx>
Add X86_CR4_FRED macro for the FRED bit in %cr4. This bit should be a
s/should/must/ no?
+/*
+ * 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)
That type cast is required because:
+#define X86_CR4_FRED _BITULL(X86_CR4_FRED_BIT)
Bah. Fred is 64 bit only. So why defining this as 1ULL << 32
unconditionally and stripping the bit off on 32bit via the type cast?
#ifdef CONFIG_X86_64
#define X86_CR4_FRED _BITUL(X86_CR4_FRED_BIT)
#else
#define X86_CR4_FRED 0
#endif
would be too obvious, right?
It also adds an #ifdef mess to avoid a simple typecast. Is that the
right tradeoff?
I'm not saying it is or it isn't, it is an open question.
-hpa
