linux-kernel - Re: [PATCH v2 1/5] x86/mm/pageattr: Ensure cpa->pfn only contains page frame numbers

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Date:	Tue, 17 Nov 2015 09:44:10 +0000
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Dave Hansen <dave.hansen@...el.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H . Peter Anvin" <hpa@...or.com>, Toshi Kani <toshi.kani@...com>,
	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
	Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH v2 1/5] x86/mm/pageattr: Ensure cpa->pfn only contains
 page frame numbers

On Mon, 16 Nov, at 07:56:17AM, Dave Hansen wrote:
> I'm glad you're looking at this. It obviously needed some love. :)
> 
> On 11/14/2015 02:00 PM, Matt Fleming wrote:
> > +	npages = (_end - _text) >> PAGE_SHIFT;
> > +	text = __pa(_text);
> > +	pfn = text >> PAGE_SHIFT;
> > +
> > +	if (kernel_map_pages_in_pgd(pgd, pfn, text, npages, 0)) {
> > +		pr_err("Failed to map kernel text 1:1\n");
> > +		return 1;
> > +	}
> 
> Are _end and _text guaranteed to be aligned?  If not, I think the
> calculation might be wrong.  Just for fun, imagine that _end=0xfff and
> _text=0x1001.  npages would be 0.
 
Bugger. Good catch, thanks.

> Some other code like set_kernel_text_rw() does alignment on _text.
> 
> One nit is that there's quite a bit going on here, like rearranging the
> phys_stack arithmetic ordering that is far beyond just simplifying the
> paddr vs. pfn issue, but that isn't called out in the changelog at all.
 
Yeah, the phys_stack hunk actually slipped into this patch by
accident. It ensures the stack is mapped into the EFI page tables.
I'll split this out.

> Your fixes all look correct to me, fwiw.

Thanks! If you could respond to the next version with an ACK or
Reviewed-by tag, that'd be great.
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