Re: [PATCHv2 5/7] x86/mm: Reserve unaccepted memory bitmap

[Dave Hansen <dave.hansen@intel.com>]

On 1/11/22 03:33, Kirill A. Shutemov wrote:
> Unaccepted memory bitmap is allocated during decompression stage and
> handed over to main kernel image via boot_params. The bitmap is used to
> track if memory has been accepted.
> 
> Reserve unaccepted memory bitmap has to prevent reallocating memory for
> other means.

I'm having a hard time parsing that changelog, especially the second 
paragraph.  Could you give it another shot?

> +	/* Mark unaccepted memory bitmap reserved */
> +	if (boot_params.unaccepted_memory) {
> +		unsigned long size;
> +
> +		/* One bit per 2MB */
> +		size = DIV_ROUND_UP(e820__end_of_ram_pfn() * PAGE_SIZE,
> +				    PMD_SIZE * BITS_PER_BYTE);
> +		memblock_reserve(boot_params.unaccepted_memory, size);
> +	}

Is it OK that the size of the bitmap is inferred from 
e820__end_of_ram_pfn()?  Is this OK in the presence of mem= and other 
things that muck with the e820?