Re: [Xen-devel] [PATCH v3 8/8] libxl, hvmloader: Don't relocate memory for MMIO hole

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.06.13 at 18:33, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
> @@ -57,6 +59,32 @@ void pci_setup(void)
>      } *bars = (struct bars *)scratch_start;
>      unsigned int i, nr_bars = 0;
>  
> +    const char *s;
> +    /*
> +     * Do we allow hvmloader to relocate guest memory in order to
> +     * increase the size of the lowmem MMIO hole?  Defaulting to 1
> +     * here will mean that non-libxl toolstacks (including xend and
> +     * home-grown ones) will experience this series as "no change".
> +     * It does mean that those using qemu-xen will still experience
> +     * the bug (described below); but it also means that those using
> +     * qemu-traditional will *not* experience any change; and it also
> +     * means that there is a work-around for those using qemu-xen,
> +     * namely switching to qemu-traditional.
> +     *
> +     * If we defaulted to 0, and failing to resize the hole caused any
> +     * problems with qemu-traditional, then there is no work-around.
> +     *
> +     * Since xend can't talk to qemu-traditional, I think this is the

qemu-xen?

> +     * option that will have the least impact.
> +     */
> +    bool allow_memory_relocate = 1;
> +
> +    s = xenstore_read(HVM_XS_ALLOW_MEMORY_RELOCATE, NULL);
> +    if ( s )
> +        allow_memory_relocate = strtoll(s, NULL, 0);
> +    printf("Relocating guest memory for lowmem MMIO space %s\n",
> +           allow_memory_relocate?"enabled":"disabled");
> +
>      /* Program PCI-ISA bridge with appropriate link routes. */
>      isa_irq = 0;
>      for ( link = 0; link < 4; link++ )
> @@ -208,8 +236,25 @@ void pci_setup(void)
>          pci_writew(devfn, PCI_COMMAND, cmd);
>      }
>  
> -    while ( (mmio_total > (pci_mem_end - pci_mem_start)) &&
> -            ((pci_mem_start << 1) != 0) )
> +    /*
> +     * At the moment qemu-xen can't deal with relocated memory regions.
> +     * It's too close to the release to make a proper fix; for now,
> +     * only allow the MMIO hole to grow large enough to move guest memory
> +     * if we're running qemu-traditional.  Items that don't fit will be
> +     * relocated into the 64-bit address space.
> +     *
> +     * This loop now does the following:
> +     * - If allow_memory_relocate, increase the MMIO hole until it's
> +     *   big enough, or until it's 2GiB
> +     * - If !allow_memory_relocate, increase the MMIO hole until it's
> +     *   big enough, or until it's 2GiB, or until it overlaps guest
> +     *   memory
> +     */
> +    while ( (mmio_total > (pci_mem_end - pci_mem_start)) 
> +            && ((pci_mem_start << 1) != 0)
> +            && (allow_memory_relocate
> +                || (((pci_mem_start << 1) >> PAGE_SHIFT)
> +                    >= hvm_info->low_mem_pgend)) )
>          pci_mem_start <<= 1;
>  
>      if ( mmio_total > (pci_mem_end - pci_mem_start) ) {
> diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
> index ac1f90e..342d2ce 100644
> --- a/tools/libxl/libxl_dm.c
> +++ b/tools/libxl/libxl_dm.c
> @@ -1154,6 +1154,12 @@ void libxl__spawn_local_dm(libxl__egc *egc, 
> libxl__dm_spawn_state *dmss)
>          libxl__xs_write(gc, XBT_NULL,
>                          libxl__sprintf(gc, "%s/hvmloader/bios", path),
>                          "%s", libxl_bios_type_to_string(b_info->u.hvm.bios));
> +        /* Disable relocating memory to make the MMIO hole larger
> +         * unless we're running qemu-traditional */
> +        libxl__xs_write(gc, XBT_NULL,
> +                        libxl__sprintf(gc, 
> "%s/hvmloader/allow-memory-relocate", path),
> +                        "%d",
> +                        
> b_info->device_model_version==LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONA
> L);
>          free(path);
>      }
>  
> diff --git a/xen/include/public/hvm/hvm_xs_strings.h 
> b/xen/include/public/hvm/hvm_xs_strings.h
> index 9042303..4de5881 100644
> --- a/xen/include/public/hvm/hvm_xs_strings.h
> +++ b/xen/include/public/hvm/hvm_xs_strings.h
> @@ -28,6 +28,7 @@
>  #define HVM_XS_HVMLOADER               "hvmloader"
>  #define HVM_XS_BIOS                    "hvmloader/bios"
>  #define HVM_XS_GENERATION_ID_ADDRESS   "hvmloader/generation-id-address"
> +#define HVM_XS_ALLOW_MEMORY_RELOCATE   "hvmloader/allow-memory-relocate"
>  
>  /* The following values allow additional ACPI tables to be added to the
>   * virtual ACPI BIOS that hvmloader constructs. The values specify the 
> guest
> -- 
> 1.7.9.5
> 
> 
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> http://lists.xen.org/xen-devel 



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