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?
> + (X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_UMIP |
> + X86_CR4_FSGSBASE | X86_CR4_CET | X86_CR4_FRED);
Thanks,
tglx
