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

[Dr. David Alan Gilbert]

* McMillan, Erich (erich.mcmillan@hp.com) wrote:
> Additionally HPi is not a mistake, corporate requires that we refer to 
> ourselves as Hewlett Packard Inc since the split in 2015. I will perhaps 
> update this to be the full name for clarity.

Please note that no one outside of HP knows what HPi is; so you might
want to spell it out a bit.

Dave

> 
> From: McMillan, Erich
> Sent: Friday, September 25, 2020 12:15 PM
> To: Laszlo Ersek <lersek@redhat.com>; qemu-devel@nongnu.org
> Cc: dgilbert@redhat.com; mst@redhat.com; marcel.apfelbaum@gmail.com; 
> imammedo@redhat.com; kraxel@redhat.com
> Subject: RE: [PATCH v5] hw/i386/pc: add max combined fw size as machine 
> configuration option
> 
> Hi Laszlo,
> 
> Thank you for the feedback, apologies that I missed the exact line references 
> I was moving too fast.
> I appreciate you taking the time to explain the nuances.
> 
> On an unrelated note, it seems that my patches are no longer appearing in 
> https://lists.nongnu.org/archive/html/qemu-devel/2020-09/index.html is this 
> because I need to cc qemu-devel@nongnu.org<mailto:qemu-devel@nongnu.org> 
> rather than –to?
> 
> -Erich
> 
> From: Laszlo Ersek [mailto:lersek@redhat.com]
> Sent: Friday, September 25, 2020 2:00 AM
> To: McMillan, Erich <erich.mcmillan@hp.com<mailto:erich.mcmillan@hp.com>>; 
> qemu-devel@nongnu.org<mailto:qemu-devel@nongnu.org>
> Cc: dgilbert@redhat.com<mailto:dgilbert@redhat.com>; 
> mst@redhat.com<mailto:mst@redhat.com>; 
> marcel.apfelbaum@gmail.com<mailto:marcel.apfelbaum@gmail.com>; 
> imammedo@redhat.com<mailto:imammedo@redhat.com>; 
> kraxel@redhat.com<mailto:kraxel@redhat.com>
> Subject: Re: [PATCH v5] hw/i386/pc: add max combined fw size as machine 
> configuration option
> 
> 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<mailto: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<mailto: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<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<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:
> >
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK