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

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Message-ID: <48F8ACF7.6050905@goop.org>
Date:	Fri, 17 Oct 2008 08:19:19 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Jan Beulich <jbeulich@...ell.com>
CC:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Chris Lalancette <clalance@...hat.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [Xen-devel] [PATCH]: Fix Xen domU boot with batched			 mprotect

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.

>> and 32-bit is similar (but simpler, since it doesn't need to worry about a separate kernel mapping).
>>     
>
> This continues to be broken, but not as badly as it used to be - while it
> now covers user space and the vmalloc area (I'm unclear why this is
> excluded only after booting completed, though), hypervisor space
> continues to not be considered here.
>
> But as mentioned before - excluding the vmalloc area seems bogus wrt
> the name of the function, but as I take it the confusion here is intended.
>   

I think a strictly correct name for the function would be 
can_i_use___pa_on_this_address(vaddr).  It isn't 
is_this_really_an_addressable_location(vaddr).

    J
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