Re: [PATCH v5] hw/i386/pc: add max combined fw size as machine configuration option

[Laszlo Ersek]

Hi Erich,

when processing review feedback, please pay attention to *where* the
review comments are inserted, in response to your patch email.

I'm pointing this out not because I want to annoy you with my
obsessions, but because I consider this discussion a kind of "git +
mailing lists" training for you. (In accordance with your first message
on the topic.)

Please see specifics below:

On 09/25/20 05:36, Erich Mcmillan wrote:
> From: Erich McMillan <erich.mcmillan@hp.com>
> 
> At HPi we have a need for increased fw size to enable testing of our custom 
> fw.
> 
> Signed-off-by: Erich McMillan <erich.mcmillan@hp.com>
> 
> Change since v4:
>      Add explicit return to pc_machine_set_max_fw_size.
>      Remove /* default */ from max_fw_size initialization.
> ---
> 
>  hw/i386/pc.c         | 52 ++++++++++++++++++++++++++++++++++++++++++++
>  hw/i386/pc_sysfw.c   | 13 ++---------
>  include/hw/i386/pc.h |  2 ++
>  3 files changed, 56 insertions(+), 11 deletions(-)

Please refer to my earlier feedback, archived at the following location:

8fdbf9f1-5125-1c39-4ec7-f99f017d4345@redhat.com">http://mid.mail-archive.com/8fdbf9f1-5125-1c39-4ec7-f99f017d4345@redhat.com

As I say in that message, the v(n)->v(n+1) changelog belongs 'between
the "---" separator and the diffstat'. In that message, I marked the
specific location with [*].

Basically the "---" separator terminates the commit message, and the
first "diff --git" line starts the code changes. What's between them is
thrown away, when the patch is applied. So in that throwaway area,
git-format-patch places the diffstat automatically (because it gives
reviewers a helpful overview of the patch, but is not useful for patch
application). And that's also the area where the v(n)->v(n+1) changelog
should be included. Traditionally, we place that log above the diffstat.

> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index d11daacc23..6e66cbbc41 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1869,6 +1869,51 @@ 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;
> +    }
> +
> +    /*
> +    * 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.
> +    */
> +    if (value > 16 * MiB) {
> +        error_setg(errp,
> +                   "User specified max allowed firmware size %" PRIu64 " is "
> +                   "greater than 16MiB. If combined firwmare size exceeds "
> +                   "16MiB the system may not boot, or experience 
> intermittent"
> +                   "stability issues.",
> +                   value);
> +    }
> +
> +    pcms->max_fw_size = value;
> +
> +    return;
> +}

This return statement is useless. Please see my review at:

de343c71-f446-c68b-d0bc-5f9db97b5a00@redhat.com">http://mid.mail-archive.com/de343c71-f446-c68b-d0bc-5f9db97b5a00@redhat.com

There I wrote, 'Please put a "return" statement here'. And, my request
was placed *exactly between* the error_setg() call and the closing brace.

The idea being that, if we take the (value > 16 * MiB) branch, then yes
we need to set the error, but we also need to abandon the rest of the
function. If "value" is invalid (out of bounds), then "pcms->max_fw_size
= value" is exactly the assignment that we do *not* want to reach.

> +
>  static void pc_machine_initfn(Object *obj)
>  {
>      PCMachineState *pcms = PC_MACHINE(obj);
> @@ -1884,6 +1929,7 @@ 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;

Thank you for dropping the comment.

Summary:

- the changelog is helpful (thanks!), it's placement is not perfect yet
- the return statement should be moved so that it terminate the (value >
16 * MiB) branch.

Also, I think "HPi" (rather than "HP") in the commit message *could* be
a typo (I'm not sure).

Thanks,
Laszlo


>  
>      pc_system_flash_create(pcms);
>      pcms->pcspk = isa_new(TYPE_PC_SPEAKER);
> @@ -2004,6 +2050,12 @@ 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 b6c0822fe3..22450ba0ef 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.
> - */
> -#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 fe52e165b2..f7c8e7cbfe 100644
> --- a/include/hw/i386/pc.h
> +++ b/include/hw/i386/pc.h
> @@ -43,6 +43,7 @@ struct PCMachineState {
>      bool smbus_enabled;
>      bool sata_enabled;
>      bool pit_enabled;
> +    uint64_t max_fw_size;
>  
>      /* NUMA information: */
>      uint64_t numa_nodes;
> @@ -59,6 +60,7 @@ struct PCMachineState {
>  #define PC_MACHINE_SMBUS            "smbus"
>  #define PC_MACHINE_SATA             "sata"
>  #define PC_MACHINE_PIT              "pit"
> +#define PC_MACHINE_MAX_FW_SIZE      "max-fw-size"
>  
>  /**
>   * PCMachineClass:
>