linux-kernel - Re: [PATCH 4/9] Vmi fix highpte

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Date:	Thu, 01 Mar 2007 22:24:06 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Chris Wright <chrisw@...s-sol.org>, Andi Kleen <ak@....de>,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/9] Vmi fix highpte

Jeremy Fitzhardinge wrote:
> Jeremy Fitzhardinge wrote:
>   
>> Hm, I don't think this interface will work for Xen.  In Xen, whenever a
>> pagetable page gets mapped, it must be mapped RO.  map_pt_hook gets
>> called after the mapping has already been created, so its too late for Xen.
>>
>> I was planning on adding kmap_atomic_pte() for use in pte_offset_map*(),
>> which would be wired through to paravirt_ops to allow Xen to make this a
>> RO mapping.  Would this be sufficient for you to do your vmi thing?
>>   
>>     
>
> Something like this (compiled, untested).
>
>     J
>
> diff -r 972e84c265cf arch/i386/kernel/paravirt.c
> --- a/arch/i386/kernel/paravirt.c	Thu Mar 01 19:12:49 2007 -0800
> +++ b/arch/i386/kernel/paravirt.c	Thu Mar 01 19:38:42 2007 -0800
> @@ -32,6 +32,7 @@
>  #include <asm/fixmap.h>
>  #include <asm/apic.h>
>  #include <asm/tlbflush.h>
> +#include <asm/highmem.h>
>  
>  /* nop stub */
>  void _paravirt_nop(void)
> @@ -605,6 +606,8 @@ struct paravirt_ops paravirt_ops = {
>  
>  	.kpte_clear_flush = native_kpte_clear_flush,
>  
> +	.kmap_atomic_pte = native_kmap_atomic_pte,
> +
>   

That doesn't quite work, since we need to know which of the two - 
KM_PTE0 or KM_PTE1 is being mapped.  But it could be moved to before the 
mapping, as you need, and take this as a parameter.

Zach
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