Re: [Xen-devel] [PATCH] iomem: Prevent Dom0 pci bus from allocating RAM as I/O space

[Fengzhe Zhang <fengzhe.zhang@xxxxxxxxx>]

On 2011/2/16 23:06, Konrad Rzeszutek Wilk wrote:
> On Wed, Feb 16, 2011 at 10:26:20PM +0800, Zhang, Fengzhe wrote:
> > iomem: Prevent Dom0 pci bus from allocating RAM as I/O space
> Is there a bug # associated with this? Is this associated with the intel-agp
> driver trying to ioremap the scratch page and bombing out?
Yes, BZ #1726. Attached serial output when system crashes. The failure 
is inside Xen hypervisor when trying to translate a pte_val from M to P.
> > In Dom0, pci bus dynamically allocates I/O address resources from memory hole 
> > within 4GB physical space, which can be RAM space not allocated to Dom0. This 
> > patch set physical RAM space to be unusable in Dom0 E820 map if they are not 
> > owned by Dom0 to prevent them from being misused as I/O address space. Dom0 is 
> > assumed to look for MMIO space only below 4GB. If this assumption is broken, 
> > additional fixes are required.
> You mention "RAM space" and then "physical RAM" misused as "I/O" address space.
>
> It sounds to me that you are trying to fix the symptomps but not the actual 
> failure - which
> is a driver trying to ioremap System RAM?
>
> Or is it that the PCI system does something like this:
>
> [    0.000000] Allocating PCI resources starting at d0000000 (gap: 
> d0000000:2ec00000)
>
> While that gap is in System RAM?
Yes.

> Can you provide the E820 that Xen sees?
>
> What does the E820 look when you boot the kernel in baremetal stage (and use 
> the mem= argument
> to make it less than normal).
Attached serial output log.

> > Signed-off-by: Fengzhe Zhang<fengzhe.zhang@xxxxxxxxx>
> >
> > diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> > index 1a1934a..f1a3896 100644
> > --- a/arch/x86/xen/setup.c
> > +++ b/arch/x86/xen/setup.c
> > @@ -189,6 +189,16 @@ char * __init xen_memory_setup(void)
> >                         end -= delta;
> >
> >                         extra_pages += PFN_DOWN(delta);
> > +
> > +                       /*
> > +                        * Set RAM below 4GB that are not owned by Dom0 to be 
> > unusable.
> > +                        * This prevents RAM-backed address space from being 
> > used as
> > +                        * I/O address in Dom0. Dom0 is assumed to look for MMIO
> > +                        * space only below 4GB. If this assumption is broken, 
> > additional
> > +                        * fixes are required.
> > +                        */
> > +                       if (delta&&  end<  0x100000000UL)
> > +                               e820_add_region(end, delta, E820_UNUSABLE);
> >                 }
> >
> >                 if (map[i].size>  0&&  end>  xen_extra_mem_start)
>
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel

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