Re: [Qemu-devel] [PATCH v4 7/8] hw: acpi: Export and share the ARM RSDP build

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 17 Dec 2018 11:48:37 +0100
Samuel Ortiz <sameo@linux.intel.com> wrote:

> Now that build_rsdp() supports building both legacy and current RSDP
> tables, we can move it to a generic folder (hw/acpi) and have the i386
> ACPI code reuse it in order to reduce code duplication.
> 
> Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> Reviewed-by: Andrew Jones <drjones@redhat.com>
> Reviewed-by: Igor Mammedov <imammedo@redhat.com>
for future reference, if one changes patch in a significant way,
one is supposed to drop Tested/Reviewed-by tags so that reviewers
would look at it again and we by mistake won't merge not actually
reviewed changes.

[...]

> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index fb877648ac..846cb6d755 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -2547,35 +2547,6 @@ build_amd_iommu(GArray *table_data, BIOSLinker *linker)
>                   "IVRS", table_data->len - iommu_start, 1, NULL, NULL);
>  }
>  
> -static void
> -build_rsdp(GArray *rsdp_table, BIOSLinker *linker, unsigned rsdt_tbl_offset)
> -{
> -    /* AcpiRsdpDescriptor describes revision 2 RSDP table and as result we
> -     * allocate extra 16 bytes for pc/q35 RSDP rev1 as well. Keep extra 16 bytes
> -     * wasted to make sure we won't breake migration for machine types older
> -     * than 2.3 due to size mismatch.
> -     */
> -    AcpiRsdpDescriptor *rsdp = acpi_data_push(rsdp_table, sizeof *rsdp);
> -    unsigned rsdt_pa_size = sizeof(rsdp->rsdt_physical_address);
> -    unsigned rsdt_pa_offset =
> -        (char *)&rsdp->rsdt_physical_address - rsdp_table->data;
> -
> -    bios_linker_loader_alloc(linker, ACPI_BUILD_RSDP_FILE, rsdp_table, 16,
> -                             true /* fseg memory */);
> -
> -    memcpy(&rsdp->signature, "RSD PTR ", 8);
> -    memcpy(rsdp->oem_id, ACPI_BUILD_APPNAME6, 6);
> -    /* Address to be filled by Guest linker */
> -    bios_linker_loader_add_pointer(linker,
> -        ACPI_BUILD_RSDP_FILE, rsdt_pa_offset, rsdt_pa_size,
> -        ACPI_BUILD_TABLE_FILE, rsdt_tbl_offset);
> -
> -    /* Checksum to be filled by Guest linker */
> -    bios_linker_loader_add_checksum(linker, ACPI_BUILD_RSDP_FILE,
> -        (char *)rsdp - rsdp_table->data, 20 /* ACPI rev 1.0 RSDP size */,
> -        (char *)&rsdp->checksum - rsdp_table->data);
> -}
> -
>  typedef
>  struct AcpiBuildState {
>      /* Copy of table in RAM (for patching). */
> @@ -2732,7 +2703,25 @@ void acpi_build(AcpiBuildTables *tables, MachineState *machine)
>                 slic_oem.id, slic_oem.table_id);
>  
>      /* RSDP is in FSEG memory, so allocate it separately */
> -    build_rsdp(tables->rsdp, tables->linker, rsdt);
> +    {
> +        AcpiRsdpData rsdp_data = {
> +            .revision = 0,
> +            .oem_id = ACPI_BUILD_APPNAME6,
> +            .xsdt_tbl_offset = NULL,
> +            .rsdt_tbl_offset = &rsdt,
> +        };
> +        build_rsdp(tables->rsdp, tables->linker, &rsdp_data);
> +        if (!pcmc->rsdp_in_ram) {
> +            /*
> +             * Legacy machine types (2.2 and older) expect to get a complete
> +             * revision 2 RSDP table, even though they only look at the
not true, rev is set to 0 for pc machines, the point of the original comment was
that we allocate extra 16 bytes but not actually using them and why it's bad
to drop it suddenly.

> +             * revision 0 fields (xsdt pointer is not set). So in order to
> +             * not break migration to those machine types we waste 16 bytes
> +             * that we amend to the RSDP revision 0 structure.
                          ^^^ added
> +             */
Perhaps amended original comment would be clearer:

   /* We used to allocate extra space for RSDP rev 2 but used only space for
    * legacy RSDP and extra bytes were zeroed out. Keep wasting extra 16 bytes
    * to make sure we won't breake migration for machine types 2.2 and older
    * due to RSDP blob size mismatch.
    */

> +            build_append_int_noprefix(tables->rsdp, 0, 16);
> +        }
> +    }
>  
>      /* We'll expose it all to Guest so we want to reduce
>       * chance of size changes.

With comment fixed:
Reviewed-by: Igor Mammedov <imammedo@redhat.com>

since it's minor fixup and doesn't affect applying remaining patches you can post
v5 7/8 as reply to v4 7/8