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 07:39:56 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	<matt@...sole-pimps.org>, <matt.fleming@...el.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 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.

Jan

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