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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

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?

> 
> 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?

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).

> 
> Signed-off-by: Fengzhe Zhang <fengzhe.zhang@intel.com>
> 
> 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@lists.xensource.com
> http://lists.xensource.com/xen-devel