Re: [Qemu-devel] [PATCH 3/5] pc: future-proof migration-compatibility of ACPI tables

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jul 28, 2014 at 05:34:16PM +0200, Paolo Bonzini wrote:
> This patch avoids that similar changes break QEMU again in the future.
> QEMU will now hard-code 64k as the maximum ACPI table size, which
> (despite being an order of magnitude smaller than 640k) should be enough
> for everyone.

Famous last words :) So what worries me here, is that we
are potentially breaking legal configurations for the
benefit of the minority that cares about cross-version
migration.

So I'm inclined to apply everything except this patch, and
instead, use the patches that I sent to make the
ram block very large, something like 1 Megabyte.

This localizes the pain to cross-version migration.


> 
> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
> Tested-by: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  hw/i386/acpi-build.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index a3d5822..25cf297 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -62,6 +62,8 @@
>  #define ACPI_BUILD_LEGACY_CPU_AML_SIZE    97
>  #define ACPI_BUILD_ALIGN_SIZE             0x1000
>  
> +#define ACPI_BUILD_TABLE_SIZE             0x10000
> +
>  typedef struct AcpiCpuInfo {
>      DECLARE_BITMAP(found_cpus, ACPI_CPU_HOTPLUG_ID_LIMIT);
>  } AcpiCpuInfo;
> @@ -1569,7 +1571,13 @@ void acpi_build(PcGuestInfo *guest_info, AcpiBuildTables *tables)
>          }
>          g_array_set_size(tables->table_data, legacy_table_size);
>      } else {
> -        acpi_align_size(tables->table_data, ACPI_BUILD_ALIGN_SIZE);
> +        if (tables->table_data->len > ACPI_BUILD_TABLE_SIZE) {
> +            /* As of QEMU 2.1, this fires with 160 VCPUs and 255 memory slots.  */
> +            error_report("ACPI tables are larger than 64k.  Please remove");
> +            error_report("CPUs, NUMA nodes, memory slots or PCI bridges.");
> +            exit(1);
> +        }
> +        g_array_set_size(tables->table_data, ACPI_BUILD_TABLE_SIZE);
>      }
>  
>      acpi_align_size(tables->linker, ACPI_BUILD_ALIGN_SIZE);
> -- 
> 1.8.3.1
>