linux-kernel - Re: [PATCH v3 RESEND 2/2] x86/mm/KASLR: Fix the size of vmemmap section

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Date:   Mon, 29 Apr 2019 16:12:46 +0800
From:   Baoquan He <bhe@...hat.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
        mingo@...nel.org, bp@...en8.de, hpa@...or.com,
        kirill.shutemov@...ux.intel.com, keescook@...omium.org,
        peterz@...radead.org, thgarnie@...gle.com,
        herbert@...dor.apana.org.au, mike.travis@....com,
        frank.ramsay@....com, yamada.masahiro@...ionext.com
Subject: Re: [PATCH v3 RESEND 2/2] x86/mm/KASLR: Fix the size of vmemmap
 section

On 04/28/19 at 09:54pm, Kirill A. Shutemov wrote:
> > @@ -109,6 +110,14 @@ void __init kernel_randomize_memory(void)
> >  	if (memory_tb < kaslr_regions[0].size_tb)
> >  		kaslr_regions[0].size_tb = memory_tb;
> >  
> > +	/**
> 
> Nit: that is weird style for inline comment.

Right, will fix.

Thanks a lot for reviewing.

> 
> > +	 * Calculate how many TB vmemmap region needs, and aligned to
> > +	 * 1TB boundary.
> > +	 */
> > +	vmemmap_size = (kaslr_regions[0].size_tb << (TB_SHIFT - PAGE_SHIFT)) *
> > +		sizeof(struct page);
> 
> Hm. Don't we need to take into account alignment requirements for struct
> page here? I'm worried about some exotic debug kernel config where
> sizeof(struct page) doesn't satify __alignof__(struct page).

I know sizeof(struct page) has handled its own struct alignment and
padding. About __alignof__(struct page), will it conflict with below
code to convert pfn < -- > page? Not sure if I got your point.

#elif defined(CONFIG_SPARSEMEM_VMEMMAP)

/* memmap is virtually contiguous.  */
#define __pfn_to_page(pfn)      (vmemmap + (pfn))
#define __page_to_pfn(page)     (unsigned long)((page) - vmemmap)

#elif...


> 
> > +	kaslr_regions[2].size_tb = DIV_ROUND_UP(vmemmap_size, 1UL << TB_SHIFT);
> > +
> >  	/* Calculate entropy available between regions */
> >  	remain_entropy = vaddr_end - vaddr_start;
> >  	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
> -- 
>  Kirill A. Shutemov