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Re: [Qemu-devel] [PATCH 3/5] pc: future-proof migration-compatibility of
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH 3/5] pc: future-proof migration-compatibility of ACPI tables |
Date: |
Mon, 28 Jul 2014 17:59:07 +0200 |
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 <address@hidden>
> Tested-by: Igor Mammedov <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
> 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
>