Re: [PATCHv6 05/30] x86/tdx: Exclude shared bit from __PHYSICAL_MASK

[Thomas Gleixner]

On Wed, Mar 16 2022 at 05:08, Kirill A. Shutemov wrote:
> @@ -82,6 +82,14 @@ void __init tdx_early_init(void)
>  
>  	cc_set_vendor(CC_VENDOR_INTEL);
>  
> +	/*
> +	 * All bits above GPA width are reserved and kernel treats shared bit
> +	 * as flag, not as part of physical address.
> +	 *
> +	 * Adjust physical mask to only cover valid GPA bits.
> +	 */
> +	physical_mask &= GENMASK_ULL(gpa_width - 2, 0);
> +

Hrm. I forgot about the second use case for gpa_width, but my comment
about ordering still stands. OTOH:

         GENMASK_ULL(gpa_width - 2, 0) == BIT_UL(gpa_width - 1) - 1

right? So you really can consolidate on the fact that cc_mask is a
single bit which is above the guests physical address space boundary.

I.e. make the code tell the story instead of adding lengthy comments
explaining the obfuscation.

Thanks,

        tglx