Re: [PATCH v3] hw/acpi: add an assertion check for non-null return from acpi_get_i386_pci_host

[Ani Sinha]

On Fri, 6 Aug 2021, Philippe Mathieu-Daudé wrote:

> On 8/6/21 4:01 PM, Philippe Mathieu-Daudé wrote:
> > On 8/6/21 12:52 PM, Ani Sinha wrote:
> >> On Fri, 6 Aug 2021, Igor Mammedov wrote:
> >>> On Thu, 5 Aug 2021 19:42:35 +0530 (IST)
> >>> Ani Sinha <ani@anisinha.ca> wrote:
> >>>> On Thu, 5 Aug 2021, Ani Sinha wrote:
> >>>>> On Thu, 5 Aug 2021, Ani Sinha wrote:
> >>>>>> On Thu, 5 Aug 2021, Igor Mammedov wrote:
> >>>>>>> On Mon, 26 Jul 2021 22:27:43 +0530
> >>>>>>> Ani Sinha <ani@anisinha.ca> wrote:
> >>>>>>>
> >>>>>>>> All existing code using acpi_get_i386_pci_host() checks for a 
> >>>>>>>> non-null
> >>>>>>>> return value from this function call. Instead of returning early 
> >>>>>>>> when the value
> >>>>>>>> returned is NULL, assert instead. Since there are only two possible 
> >>>>>>>> host buses
> >>>>>>>> for i386 - q35 and i440fx, a null value return from the function 
> >>>>>>>> does not make
> >>>>>>>> sense in most cases and is likely an error situation.
> >>>>>>>>
> >>>>>>>> Fixes: c0e427d6eb5fef ("hw/acpi/ich9: Enable ACPI PCI hot-plug")
> >>>>>>>>
> >>>>>>>> Signed-off-by: Ani Sinha <ani@anisinha.ca>
> >>>>>>>> ---
> >>>>>>>>  hw/acpi/pcihp.c      |  8 ++++++++
> >>>>>>>>  hw/i386/acpi-build.c | 15 ++++++---------
> >>>>>>>>  2 files changed, 14 insertions(+), 9 deletions(-)
> >>>>>>>>
> >>>>>>>> changelog:
> >>>>>>>> v1: initial patch
> >>>>>>>> v2: removed comment addition - that can be sent as a separate patch.
> >>>>>>>> v3: added assertion for null host values for all cases except one.
> >>>>>>>>
> >>>>>>>> diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
> >>>>>>>> index f4d706e47d..054ee8cbc5 100644
> >>>>>>>> --- a/hw/acpi/pcihp.c
> >>>>>>>> +++ b/hw/acpi/pcihp.c
> >>>>>>>> @@ -116,6 +116,12 @@ static void acpi_set_pci_info(void)
> >>>>>>>>      bsel_is_set = true;
> >>>>>>>>
> >>>>>>>>      if (!host) {
> >>>>>>>> +        /*
> >>>>>>>> +         * This function can be eventually called from
> >>>>>>>> +         * qemu_devices_reset() -> acpi_pcihp_reset() even
> >>>>>>>> +         * for architectures other than i386. Hence, we need
> >>>>>>>> +         * to ignore null values for host here.
> >>>>>>>> +         */
> >>>>>>>>          return;
> >>>>>>>>      }
> >>>>>>>
> >>>>>>> I suspect it's a MIPS target that call this code unnecessarily.
> >>>>>>> It would be better to get rid of this condition altogether.
> >>>>>>> Frr that I can suggest to make acpi_pcihp_reset() stub and
> >>>>>>> replace pcihp.c with stub (perhaps use acpi-x86-stub.c) when building
> >>>>>>> for MIPS.
> >>>>>>>
> >>>>>>> then a bunch of asserts/ifs won't be necessary,
> >>>>>>> just one in acpi_get_i386_pci_host() will be sufficient.
> >>>>>>>
> >>>>>>
> >>>>>> OK this is a good idea.
> >>>>>> I can see that mips-softmmu-config-devices.h has
> >>>>>> CONFIG_ACPI_X86 turned on for mips. This does not seem right.
> >>>>>>
> >>>>>> The issue here is:
> >>>>>>
> >>>>>> $ grep -R CONFIG_ACPI_X86 *
> >>>>>> devices/mips-softmmu/common.mak:CONFIG_ACPI_X86=y
> >>>>>>
> >>>>>> So after
> >>>>>>
> >>>>>> -CONFIG_ACPI_X86=y
> >>>>>> -CONFIG_PIIX4=y
> >>>>>>
> >>>>>> (the second one is needed because after removing first one we get:
> >>>>>>
> >>>>>> /usr/bin/ld: libcommon.fa.p/hw_isa_piix4.c.o: in function 
> >>>>>> `piix4_create':
> >>>>>> /home/anisinha/workspace/qemu/build/../hw/isa/piix4.c:269: undefined
> >>>>>> reference to `piix4_pm_init'
> >>>>>>
> >>>>>> This is because in hw/acpi/meson.build, piix4.c is conditional on
> >>>>>> CONFIG_ACPI_X86. )
> >>>>>>
> >>>>>> /usr/bin/ld: libqemu-mips-softmmu.fa.p/hw_mips_gt64xxx_pci.c.o: in
> >>>>>> function `gt64120_pci_set_irq':
> >>>>>> /home/anisinha/workspace/qemu/build/../hw/mips/gt64xxx_pci.c:1020:
> >>>>>> undefined reference to `piix4_dev'
> >>>>>> /usr/bin/ld: libqemu-mips-softmmu.fa.p/hw_mips_malta.c.o: in function
> >>>>>> `mips_malta_init':
> >>>>>> /home/anisinha/workspace/qemu/build/../hw/mips/malta.c:1404: undefined
> >>>>>> reference to `piix4_create'
> >>>>>>
> >>>>>> So should mips be doing piix stuff anyway? Is Piix4 etc not x86 
> >>>>>> specific?
> >
> > PIIX, PIIX3 and PIIX4 are generic chipsets, not X86-specific.
> >
> > QEMU's PIIX3 is a Frankenstein to support virtualization to a chipset
> > not designed for it.
> > If you look at it, the X86 machine use a PIIX3 but the PIIX3 doesn't
> > even provide an ACPI function. It appeared in the PIIX4. The kludge is
> > to instanciate the PIIX4.acpi from the PIIX3 and X86 ppl are happy with
> > it, but it makes it ugly for the other architectures.
> >
> >>>>> Apparently this is by design:
> >>>>> https://qemu.readthedocs.io/en/stable/system/target-mips.html
> >
> > What do you mean "by design"? The Malta uses a PIIX4 chipset for its
> > southbridge indeed.
> >
> >>>>> which means mips malta will continue to use the x86 specific functions
> >>>>> like acpi_pcihp_reset(). Creating a stub for this with acpi-x86-stub.c
> >>>>> will result in a double symbol definition because CONFIG_PC is off for
> >>>>> mips.
> >>>>>
> >>>>
> >>>> Also to be noted that there is a stub for acpi_get_i386_pci_host() which
> >>>> simply returns NULL. This activates when CONFIG_PC is disabled. It is 
> >>>> this
> >>>> stub that gets called for mips and hence the check for non-null host is
> >>>> needed in acpi_set_pci_info() function.
> >>> that were half measures to deal around code that shouldn't be called,
> >>> now with pcihp being used by both pc and q35 we don't have reason to
> >>> keep around null checks modulo mips calling code that shouldn't be
> >>> called there to begin with.
> >>
> >> So malta mips does not need ACPI hotplug? In that case, maybe we should
> >> not make pcihp.c dependent on CONFIG_ACPI_X86. Ideas welcome.
> >
> > Linux on Malta does use the ACPI features from the PIIX4.
> >
> > Please dig in the archives, Igor / myself already argued enough about
> > this topic 2 years ago. The consensus was "yes, it is badly implemented,
> > but it works and we don't have time to get it cleaner, pc machine is
> > way more used than the malta one, so let not break the pc machines."
> >
> > See:
> > https://www.mail-archive.com/qemu-devel@nongnu.org/msg613194.html
> > https://www.mail-archive.com/qemu-devel@nongnu.org/msg690435.html
> > https://www.mail-archive.com/qemu-devel@nongnu.org/msg725504.html
>
> Also:
> https://gitlab.com/qemu-project/qemu/-/issues/193
> https://gitlab.com/qemu-project/qemu/-/issues/221

Thanks Phil for the contexts. I will go through them. For now, should we
simply go with my v2 then?