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

[Philippe Mathieu-Daudé]

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