Re: [PATCH v2 2/3] x86/mm/KASLR: Calculate the actual size of vmemmap region

[Baoquan He]

On 09/10/18 at 08:11am, Ingo Molnar wrote:
> 
> * Baoquan He <bhe@xxxxxxxxxx> wrote:
> 
> > @@ -108,6 +109,14 @@ void __init kernel_randomize_memory(void)
> >  	if (memory_tb < kaslr_regions[0].size_tb)
> >  		kaslr_regions[0].size_tb = memory_tb;
> >  
> > +	/*
> > +	 * Calculate how many TB vmemmap region needs, and align to
> > +	 * 1TB boundary.
> > +	 * */
> 
> Yeah, so that's not the standard comment style ...

Sorry for this, Will change. Thanks.

About clean up you suggested, I have made two patches and paste them at
below. Please help check if it's OK. Thanks a lot.

> So I get the part where the 'base' pointer is essentially pointers to various global variables 
> used by the MM to get the virtual base address of the kernel, vmalloc and vmemmap areas from, 
> which base addresses can thus be modified by the very early KASLR code to dynamically shape the 
> virtual memory layout of these kernel memory areas on a per bootup basis.
> 
> (BTW., that would be a great piece of information to add for the uninitiated. It's not like 
> it's obvious!)
> 
> But what does 'size_tb' do? Nothing explains it and your patch doesn't make it clearer either. 
> Also, get_padding() looks like an unnecessary layer of obfuscation:

Yes, I agree. Have made an patch according to your suggestion, paste
it here: