Re: [Xen-devel] Re: Linux Stubdom Problem

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

> 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.

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