Re: [Xen-devel] [PATCH 1/2] x86/xen: do not identity map UNUSABLE regions in the machine E820

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

On Fri, Aug 16, 2013 at 03:42:55PM +0100, David Vrabel wrote:
> From: David Vrabel <david.vrabel@xxxxxxxxxx>
> 
> If there are UNUSABLE regions in the machine memory map, dom0 will
> attempt to map them 1:1 which is not permitted by Xen and the kernel
> will crash.
> 
> There isn't anything interesting in the UNUSABLE region that the dom0
> kernel needs access to so we can avoid making the 1:1 mapping and
> treat it as RAM.
> 
> We only do this for dom0, as we do not expect any domU to ever have a
> UNUSABLE region in their pseudo-physical map.

Hm, you are going to be disappointed that this is in libxl:

        /* Lastly, convert the RAM to UNSUABLE. Look in the Linux kernel        
           at git commit 2f14ddc3a7146ea4cd5a3d1ecd993f85f2e4f948               
            "xen/setup: Inhibit resource API from using System RAM E820         
           gaps as PCI mem gaps" for full explanation. */                       
        if (end > ram_end)                                                      
            src[i].type = E820_UNUSABLE;                                        
    }                                           
> 
> This fixes a boot failure on hosts with tboot.
> 
> tboot marks a region in the e820 map as unusable and the dom0 kernel
> would attempt to map this region and Xen does not permit unusable
> regions to be mapped by guests.
> 
>   (XEN)  0000000000000000 - 0000000000060000 (usable)
>   (XEN)  0000000000060000 - 0000000000068000 (reserved)
>   (XEN)  0000000000068000 - 000000000009e000 (usable)
>   (XEN)  0000000000100000 - 0000000000800000 (usable)
>   (XEN)  0000000000800000 - 0000000000972000 (unusable)
> 
> tboot marked this region as unusable.
> 
>   (XEN)  0000000000972000 - 00000000cf200000 (usable)
>   (XEN)  00000000cf200000 - 00000000cf38f000 (reserved)
>   (XEN)  00000000cf38f000 - 00000000cf3ce000 (ACPI data)
>   (XEN)  00000000cf3ce000 - 00000000d0000000 (reserved)
>   (XEN)  00000000e0000000 - 00000000f0000000 (reserved)
>   (XEN)  00000000fe000000 - 0000000100000000 (reserved)
>   (XEN)  0000000100000000 - 0000000630000000 (usable)
> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> ---
>  arch/x86/xen/setup.c |   21 +++++++++++++++++++++
>  1 files changed, 21 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index 056d11f..5a093b7 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -313,6 +313,17 @@ static void xen_align_and_add_e820_region(u64 start, u64 
> size, int type)
>       e820_add_region(start, end - start, type);
>  }
>  
> +void xen_ignore_unusable(struct e820entry *list, size_t map_size)
> +{
> +     struct e820entry *entry;
> +     unsigned int i;
> +
> +     for (i = 0, entry = list; i < map_size; i++, entry++) {
> +             if (entry->type == E820_UNUSABLE)
> +                     entry->type = E820_RAM;
> +     }
> +}
> +
>  /**
>   * machine_specific_memory_setup - Hook for machine specific memory setup.
>   **/
> @@ -353,6 +364,16 @@ char * __init xen_memory_setup(void)
>       }
>       BUG_ON(rc);
>  
> +     /*
> +      * Xen won't allow a 1:1 mapping to be created to UNUSABLE
> +      * regions, so if we're using the machine memory map leave the
> +      * region as RAM as it is in the pseudo-physical map.
> +      *
> +      * UNUSABLE regions are not expected in domUs.
> +      */
> +     if (xen_initial_domain())
> +             xen_ignore_unusable(map, memmap.nr_entries);
> +
>       /* Make sure the Xen-supplied memory map is well-ordered. */
>       sanitize_e820_map(map, memmap.nr_entries, &memmap.nr_entries);
>  
> -- 
> 1.7.2.5
> 

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