Re: [PATCH 2/2] add maximum combined fw size as machine configuration option

[Laszlo Ersek]

On 09/18/20 10:31, Daniel P. Berrangé wrote:
> On Fri, Sep 18, 2020 at 04:23:39AM +0000, Erich Mcmillan wrote:
>> From: Erich McMillan <erich.mcmillan@hp.com>
>>
>> Signed-off-by: Erich McMillan <erich.mcmillan@hp.com>
>> ---
>>  hw/i386/pc.c         | 40 ++++++++++++++++++++++++++++++++++++++++
>>  hw/i386/pc_sysfw.c   | 13 ++-----------
>>  include/hw/i386/pc.h | 22 ++++++++++++----------
>>  3 files changed, 54 insertions(+), 21 deletions(-)
>>
>> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
>> index d11daac..b304988 100644
>> --- a/hw/i386/pc.c
>> +++ b/hw/i386/pc.c
>> @@ -1869,6 +1869,39 @@ static void pc_machine_set_max_ram_below_4g(Object 
>> *obj, Visitor *v,
>>      pcms->max_ram_below_4g = value;
>>  }
>>  
>> +static void pc_machine_get_max_fw_size(Object *obj, Visitor *v,
>> +                                             const char *name, void *opaque,
>> +                                             Error **errp)
>> +{
>> +    PCMachineState *pcms = PC_MACHINE(obj);
>> +    uint64_t value = pcms->max_fw_size;
>> +
>> +    visit_type_size(v, name, &value, errp);
>> +}
>> +
>> +static void pc_machine_set_max_fw_size(Object *obj, Visitor *v,
>> +                                             const char *name, void *opaque,
>> +                                             Error **errp)
>> +{
>> +    PCMachineState *pcms = PC_MACHINE(obj);
>> +    Error *error = NULL;
>> +    uint64_t value;
>> +
>> +    visit_type_size(v, name, &value, &error);
>> +    if (error) {
>> +        error_propagate(errp, error);
>> +        return;
>> +    }
>> +
> 
> Just here we should have a comment explaining why we pick this max limit.
> The comment you removed later can be transplanted to here...
> 
>> +    if (value > 16 * MiB) {
>> +        warn_report("User specifed max allowed firmware size %" PRIu64 " is 
>> greater than 16MiB,"
>> +                    "if combined firwmare size exceeds 16MiB system may not 
>> boot,"
>> +                    "or experience intermittent stability issues.", value);
>> +    }
>> +
>> +    pcms->max_fw_size = value;
>> +}
>> +
>>  static void pc_machine_initfn(Object *obj)
>>  {
>>      PCMachineState *pcms = PC_MACHINE(obj);
>> @@ -1884,6 +1917,7 @@ static void pc_machine_initfn(Object *obj)
>>      pcms->smbus_enabled = true;
>>      pcms->sata_enabled = true;
>>      pcms->pit_enabled = true;
>> +    pcms->max_fw_size = 8 * MiB;
>>  
>>      pc_system_flash_create(pcms);
>>      pcms->pcspk = isa_new(TYPE_PC_SPEAKER);
>> @@ -2004,6 +2038,12 @@ static void pc_machine_class_init(ObjectClass *oc, 
>> void *data)
>>  
>>      object_class_property_add_bool(oc, PC_MACHINE_PIT,
>>          pc_machine_get_pit, pc_machine_set_pit);
>> +
>> +    object_class_property_add(oc, PC_MACHINE_MAX_FW_SIZE, "size",
>> +        pc_machine_get_max_fw_size, pc_machine_set_max_fw_size,
>> +        NULL, NULL);
>> +    object_class_property_set_description(oc, PC_MACHINE_MAX_FW_SIZE,
>> +        "Maximum combined firmware size");
>>  }
>>  
>>  static const TypeInfo pc_machine_info = {
>> diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
>> index b6c0822..22450ba 100644
>> --- a/hw/i386/pc_sysfw.c
>> +++ b/hw/i386/pc_sysfw.c
>> @@ -39,15 +39,6 @@
>>  #include "hw/block/flash.h"
>>  #include "sysemu/kvm.h"
>>  
>> -/*
>> - * We don't have a theoretically justifiable exact lower bound on the base
>> - * address of any flash mapping. In practice, the IO-APIC MMIO range is
>> - * [0xFEE00000..0xFEE01000] -- see IO_APIC_DEFAULT_ADDRESS --, leaving free
>> - * only 18MB-4KB below 4G. For now, restrict the cumulative mapping to 8MB 
>> in
>> - * size.
>> - */
> 
> ....this comment should be transplanted above^^
> 
>> -#define FLASH_SIZE_LIMIT (8 * MiB)
>> -
>>  #define FLASH_SECTOR_SIZE 4096
>>  
>>  static void pc_isa_bios_init(MemoryRegion *rom_memory,
>> @@ -182,10 +173,10 @@ static void pc_system_flash_map(PCMachineState *pcms,
>>          }
>>          if ((hwaddr)size != size
>>              || total_size > HWADDR_MAX - size
>> -            || total_size + size > FLASH_SIZE_LIMIT) {
>> +            || total_size + size > pcms->max_fw_size) {
>>              error_report("combined size of system firmware exceeds "
>>                           "%" PRIu64 " bytes",
>> -                         FLASH_SIZE_LIMIT);
>> +                         pcms->max_fw_size);
>>              exit(1);
>>          }
>>  
>> diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
>> index fe52e16..cae213d 100644
>> --- a/include/hw/i386/pc.h
>> +++ b/include/hw/i386/pc.h
>> @@ -39,10 +39,11 @@ struct PCMachineState {
>>      uint64_t max_ram_below_4g;
>>      OnOffAuto vmport;
>>  
>> -    bool acpi_build_enabled;
>> -    bool smbus_enabled;
>> -    bool sata_enabled;
>> -    bool pit_enabled;
>> +    bool     acpi_build_enabled;
>> +    bool     smbus_enabled;
>> +    bool     sata_enabled;
>> +    bool     pit_enabled;
>> +    uint64_t max_fw_size;
> 
> Don't change whitespace in the existing fields - trying to
> horizontally align fields has no benefit and needlessly
> creates bigger diffs.
> 
>>  
>>      /* NUMA information: */
>>      uint64_t numa_nodes;
>> @@ -52,13 +53,14 @@ struct PCMachineState {
>>      hwaddr memhp_io_base;
>>  };
>>  
>> -#define PC_MACHINE_ACPI_DEVICE_PROP "acpi-device"
>> -#define PC_MACHINE_MAX_RAM_BELOW_4G "max-ram-below-4g"
>> +#define PC_MACHINE_ACPI_DEVICE_PROP   "acpi-device"
>> +#define PC_MACHINE_MAX_RAM_BELOW_4G   "max-ram-below-4g"
>>  #define PC_MACHINE_DEVMEM_REGION_SIZE "device-memory-region-size"
>> -#define PC_MACHINE_VMPORT           "vmport"
>> -#define PC_MACHINE_SMBUS            "smbus"
>> -#define PC_MACHINE_SATA             "sata"
>> -#define PC_MACHINE_PIT              "pit"
>> +#define PC_MACHINE_VMPORT             "vmport"
>> +#define PC_MACHINE_SMBUS              "smbus"
>> +#define PC_MACHINE_SATA               "sata"
>> +#define PC_MACHINE_PIT                "pit"
>> +#define PC_MACHINE_MAX_FW_SIZE        "max-fw-size"
> 
> Same here, just don't change whitespace alignment please.

On a total tangent: I'm generally OK with changing whitespace for lining
up stuff visually, but whenever that's done, IMO it should be the *only*
thing done in a patch. First add the amount of whitespace that you know
you're going to need, to the existent fields / macros, and then
introduce the new fields / macros.

But, I understand that some maintainers dislike even that approach,
because it makes "git-blame" a bit more cumbersome to use. (The first
git-blame invocation gives you the whitespace-changing commit, and you
have to rerun git-blame at the *parent* of that commit, to get what you
actually want.)

Tangent ends, anyway...

Thanks
Laszlo