From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: Re: Linux Stubdom Problem
Date: Wed, 9 Nov 2011 12:05:38 -0500
Message-ID: <20111109170538.GA987@phenom.dumpdata.com>
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To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, Ian Campbell <Ian.Campbell@citrix.com>, "Tim (Xen.org)" <tim@xen.org>, Anthony PERARD <anthony.perard@gmail.com>, Keir Fraser <keir.xen@gmail.com>, Jiageng Yu <yujiageng734@gmail.com>, Samuel@rcsinet13.oracle.com, Thibault <samuel.thibault@ens-lyon.org>, Konrad@rcsinet13.oracle.com
List-Id: xen-devel@lists.xenproject.org

> The real fix should something along these lines:
> 
> 
> 
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index 3dd53f9..f2fadfc 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -422,7 +422,7 @@ static pteval_t xen_pte_val(pte_t pte)
>  		pteval = (pteval & ~_PAGE_PAT) | _PAGE_PWT;
>  	}
>  
> -	if (xen_initial_domain() && (pteval & _PAGE_IOMAP))
> +	if (pteval & _PAGE_IOMAP)
>  		return pteval;
>  
>  	return pte_mfn_to_pfn(pteval);
> @@ -483,8 +483,7 @@ static pte_t xen_make_pte(pteval_t pte)
>  	 * mappings are just dummy local mappings to keep other
>  	 * parts of the kernel happy.
>  	 */
> -	if (unlikely(pte & _PAGE_IOMAP) &&
> -	    (xen_initial_domain() || addr >= ISA_END_ADDRESS)) {
> +	if (unlikely(pte & _PAGE_IOMAP)) {
>  		pte = iomap_pte(pte);
>  	} else {
>  		pte &= ~_PAGE_IOMAP;
> ---
> 
> Could you please confirm whether this patch fixes your problem?
> 
> Konrad, do you know if this could have any unintended consequences?
> I don't think it can be a problem security wise because Xen is going to
> do all the permission checks anyway.
> The only problem I can see is if a domU is going to call xen_make_pte
> with _PAGE_IOMAP and a pfn->mfn translation is supposed to happen.

I am not sure. I think I tried this at some point but ran in some problems, but
I can't recall which ones. Let me stick this in my #testing branch and see how it
fares with Dom0/DomU/DomU PCI/ etc.