Re: [Xen-devel] [PATCH] tools/hvmloader: move shared_info to reserved memory area

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 24/10/2012 10:57, "Olaf Hering" <olaf@xxxxxxxxx> wrote:

> # HG changeset patch
> # User Olaf Hering <olaf@xxxxxxxxx>
> # Date 1351101387 -7200
> # Node ID 6a0c73ae9ce5cca72f788c0e0f8fd6872010d83e
> # Parent  22e08c9ac770db07c3c3e7c844aa7153050939f3
> tools/hvmloader: move shared_info to reserved memory area
> 
> Reserve a range of 1MB for the HVM shared info page at 0xFE700000. This
> area is already marked as reserved in the E820 map. The purpose of this
> change is to provide Linux PVonHVM guests with a fixed page outside of
> ordinary RAM. If the shared page is located in RAM it would be
> overwritten during a kexec boot.

I don't think hvmloader actually needs to map shared-info to the new
location, it justs needs to guarantee that this location is unused, and
document it so that it never *becomes* used in future.

Which can be as simple as the attached patch (in fact all the changes apart
from introducing GUEST_RESERVED_{START,END} are really cleaning up and
bug-fixing the out-of-space checks in the mem_hole_alloc/mem_alloc
functions).

This then just requires that the guest maps shared-info to FE700000 itself.
Should be quite easy. :)

 -- Keir

> Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
> 
> diff -r 22e08c9ac770 -r 6a0c73ae9ce5 tools/firmware/hvmloader/config.h
> --- a/tools/firmware/hvmloader/config.h
> +++ b/tools/firmware/hvmloader/config.h
> @@ -68,6 +68,8 @@ extern unsigned long pci_mem_start, pci_
>  /* NB. ACPI_INFO_PHYSICAL_ADDRESS *MUST* match definition in acpi/dsdt.asl!
> */
>  #define ACPI_INFO_PHYSICAL_ADDRESS    0xFC000000
>  #define RESERVED_MEMORY_DYNAMIC       0xFC001000
> +#define HVM_SHARED_INFO_AREA          0xFE700000
> +#define HVM_SHARED_INFO_SIZE          0x00100000
>  
>  extern unsigned long scratch_start;
>  
> diff -r 22e08c9ac770 -r 6a0c73ae9ce5 tools/firmware/hvmloader/util.c
> --- a/tools/firmware/hvmloader/util.c
> +++ b/tools/firmware/hvmloader/util.c
> @@ -433,11 +433,18 @@ void *mem_alloc(uint32_t size, uint32_t
>      if ( align < 16 )
>          align = 16;
>  
> +retry:
>      s = (reserve + align) & ~(align - 1);
>      e = s + size - 1;
>  
>      BUG_ON((e < s) || (e >> PAGE_SHIFT) >= hvm_info->reserved_mem_pgstart);
>  
> +    /* Skip the shared info region */
> +    if (s <= HVM_SHARED_INFO_AREA && e >= HVM_SHARED_INFO_AREA) {
> +     reserve = HVM_SHARED_INFO_AREA + HVM_SHARED_INFO_SIZE - 1;
> +     goto retry;
> +    }
> +
>      while ( (reserve >> PAGE_SHIFT) != (e >> PAGE_SHIFT) )
>      {
>          reserve += PAGE_SIZE;
> @@ -765,7 +772,7 @@ struct shared_info *get_shared_info(void
>      xatp.domid = DOMID_SELF;
>      xatp.space = XENMAPSPACE_shared_info;
>      xatp.idx   = 0;
> -    xatp.gpfn  = mem_hole_alloc(1);
> +    xatp.gpfn  = HVM_SHARED_INFO_AREA >> PAGE_SHIFT;
>      shared_info = (struct shared_info *)(xatp.gpfn << PAGE_SHIFT);
>      if ( hypercall_memory_op(XENMEM_add_to_physmap, &xatp) != 0 )
>          BUG();
> 
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