linux-kernel - Re: [Xen-devel] [PATCH]: Fix Xen domU boot with batched mprotect

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Date:	Fri, 17 Oct 2008 16:30:44 +0100
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"Chris Lalancette" <clalance@...hat.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH]: Fix Xen domU boot with batched			
	 mprotect

>>> Jeremy Fitzhardinge <jeremy@...p.org> 17.10.08 17:19 >>>
>Jan Beulich wrote:
>>>>> Jeremy Fitzhardinge <jeremy@...p.org> 16.10.08 18:10 >>>
>>>>>         
>>> The current x86-64 implementation is:
>>>
>>> bool __virt_addr_valid(unsigned long x)
>>> {
>>> 	if (x >= __START_KERNEL_map) {
>>> 		x -= __START_KERNEL_map;
>>> 		if (x >= KERNEL_IMAGE_SIZE)
>>> 			return false;
>>>     
>>
>> This, imo, is still broken (i.e. the name of the function still isn't matched
>> by the implementation): KERNEL_IMAGE_SIZE is a constant and doesn't
>> account for the fact that only the real kernel image can be relied upon
>> to be mapped.
>>   
>
>Perhaps, but I don't think it matters too much.  Unless you have a tiny 
>amount of physical memory, locations in the kernel mapping beyond the 
>actual kernel will still resolve to proper locations in the linear map.

Is e.g. 256Mb tiny? KERNEL_IMAGE_SIZE these days is 512Mb... Indeed,
when it was 40Mb (up until a few releases ago), this indeed wouldn't
matter.

Jan

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