Re: [PATCHv4 3/8] efi/x86: Implement support for unaccepted memory

[Borislav Petkov]

On Fri, Apr 08, 2022 at 10:26:14AM -0700, Dave Hansen wrote:
> > +	/*
> > +	 * Accept small regions that might not be able to be represented
> > +	 * in the bitmap:
> > +	 */
> > +	if (end - start < 2 * PMD_SIZE) {
> > +		__accept_memory(start, end);
> > +		return;
> > +	}
> 
> This is not my first time looking at this code and I still had to think
> about this a bit.  That's not good.  That pathological case here is
> actually something like this:
> 
> | 4k | 2044k + 2044k | 4k |
> ^ 0x0 	     ^ 2MB	  ^ 4MB
> 
> Where we have a 2MB-aligned 4k accepted area, a 4088k unaccepted area,
> then another 4k accepted area.  That will not result in any bits being
> set in the accepted memory bitmap because no 2MB region is fully accepted.

I could use that ascii art very well in a comment above it instead of
having to paint it in my mind each time.

Thx.

-- 
Regards/Gruss,
    Boris.

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