linux-kernel - Re: [PATCH 1/3] x86, mm: Include the entire kernel memory map in trampoline

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Date:	Fri, 05 Oct 2012 07:48:00 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, mingo@...nel.org, x86@...nel.org,
	mjg@...hat.com, linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] x86, mm: Include the entire kernel memory map in
 trampoline_pgd

On Fri, 2012-10-05 at 07:39 +0100, Jan Beulich wrote:
> >>> On 04.10.12 at 23:08, "H. Peter Anvin" <hpa@...or.com> wrote:
> > On 10/03/2012 06:31 AM, Jan Beulich wrote:
> >>>>> Matt Fleming <matt@...sole-pimps.org> 10/03/12 2:59 PM >>>
> >>> +static int insert_identity_mapping(resource_size_t paddr, unsigned long 
> > vaddr,
> >>> +                    unsigned long size)
> >>> +{
> >>> +    unsigned long end = vaddr + size;
> >>> +    unsigned long next;
> >>> +    pgd_t *vpgd, *ppgd;
> >>> +
> >>> +#ifdef CONFIG_X86_32
> >>> +    ppgd = initial_page_table + pgd_index(paddr);
> >>> +
> >>> +    if (paddr >= PAGE_OFFSET || paddr + size > PAGE_OFFSET)
> >>> +        return 1;
> >>> +#else
> >>> +    ppgd = __va(real_mode_header->trampoline_pgd) + pgd_index(paddr);
> >>
> >> Missing equivalent code (to the 32-bit one above) here - after all, you're 
> > trying
> >> to potentially insert a 52-bit physical address into 48-bit virtual space.
> >>
> > 
> > We should have the check, but at least for Linux support we require
> > P <= V-2.
> 
> Not really imo - P <= V - 1 should be sufficient here, as all that is
> necessary is that the result represents a 1:1 mapping. Specifically,
> there's no constraint to the virtual space limitation of the direct
> mapping of RAM.

Just to be clear, I was going to add this check,

        /* Don't map over the guard hole. */
        if (paddr >= 0x7fffffffffff || paddr + size > 0x7fffffffffff)
                return 1;

Since I'm guessing mapping over the guard hole would be bad. 

-- 
Matt Fleming, Intel Open Source Technology Center

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