Re: [PATCH v2] iommu/vt-d: Make DMAR_UNITS_SUPPORTED a config setting

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2022/6/15 05:12, Steve Wahl wrote:
> On Tue, Jun 14, 2022 at 12:01:45PM -0700, Jerry Snitselaar wrote:
>> On Tue, Jun 14, 2022 at 11:45:35AM -0500, Steve Wahl wrote:
>>> On Tue, Jun 14, 2022 at 10:21:29AM +0800, Baolu Lu wrote:
>>>> On 2022/6/14 09:54, Jerry Snitselaar wrote:
>>>>> On Mon, Jun 13, 2022 at 6:51 PM Baolu Lu <baolu.lu@linux.intel.com> wrote:
>>>>>>
>>>>>> On 2022/6/14 09:44, Jerry Snitselaar wrote:
>>>>>>> On Mon, Jun 13, 2022 at 6:36 PM Baolu Lu<baolu.lu@linux.intel.com>  wrote:
>>>>>>>> On 2022/6/14 04:57, Jerry Snitselaar wrote:
>>>>>>>>> On Thu, May 12, 2022 at 10:13:09AM -0500, Steve Wahl wrote:
>>>>>>>>>> To support up to 64 sockets with 10 DMAR units each (640), make the
>>>>>>>>>> value of DMAR_UNITS_SUPPORTED adjustable by a config variable,
>>>>>>>>>> CONFIG_DMAR_UNITS_SUPPORTED, and make it's default 1024 when MAXSMP is
>>>>>>>>>> set.
>>>>>>>>>>
>>>>>>>>>> If the available hardware exceeds DMAR_UNITS_SUPPORTED (previously set
>>>>>>>>>> to MAX_IO_APICS, or 128), it causes these messages: "DMAR: Failed to
>>>>>>>>>> allocate seq_id", "DMAR: Parse DMAR table failure.", and "x2apic: IRQ
>>>>>>>>>> remapping doesn't support X2APIC mode x2apic disabled"; and the system
>>>>>>>>>> fails to boot properly.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Steve Wahl<steve.wahl@hpe.com>
>>>>>>>>>> ---
>>>>>>>>>>
>>>>>>>>>> Note that we could not find a reason for connecting
>>>>>>>>>> DMAR_UNITS_SUPPORTED to MAX_IO_APICS as was done previously.  Perhaps
>>>>>>>>>> it seemed like the two would continue to match on earlier processors.
>>>>>>>>>> There doesn't appear to be kernel code that assumes that the value of
>>>>>>>>>> one is related to the other.
>>>>>>>>>>
>>>>>>>>>> v2: Make this value a config option, rather than a fixed constant.  The default
>>>>>>>>>> values should match previous configuration except in the MAXSMP case.  Keeping the
>>>>>>>>>> value at a power of two was requested by Kevin Tian.
>>>>>>>>>>
>>>>>>>>>>      drivers/iommu/intel/Kconfig | 6 ++++++
>>>>>>>>>>      include/linux/dmar.h        | 6 +-----
>>>>>>>>>>      2 files changed, 7 insertions(+), 5 deletions(-)
>>>>>>>>>>
>>>>>>>>>> diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig
>>>>>>>>>> index 247d0f2d5fdf..fdbda77ac21e 100644
>>>>>>>>>> --- a/drivers/iommu/intel/Kconfig
>>>>>>>>>> +++ b/drivers/iommu/intel/Kconfig
>>>>>>>>>> @@ -9,6 +9,12 @@ config DMAR_PERF
>>>>>>>>>>      config DMAR_DEBUG
>>>>>>>>>>         bool
>>>>>>>>>>
>>>>>>>>>> +config DMAR_UNITS_SUPPORTED
>>>>>>>>>> +    int "Number of DMA Remapping Units supported"
>>>>>>>>> Also, should there be a "depends on (X86 || IA64)" here?
>>>>>>>> Do you have any compilation errors or warnings?
>>>>>>>>
>>>>>>>> Best regards,
>>>>>>>> baolu
>>>>>>>>
>>>>>>> I think it is probably harmless since it doesn't get used elsewhere,
>>>>>>> but our tooling was complaining to me because DMAR_UNITS_SUPPORTED was
>>>>>>> being autogenerated into the configs for the non-x86 architectures we
>>>>>>> build (aarch64, s390x, ppcle64).
>>>>>>> We have files corresponding to the config options that it looks at,
>>>>>>> and I had one for x86 and not the others so it noticed the
>>>>>>> discrepancy.
>>>>>>
>>>>>> So with "depends on (X86 || IA64)", that tool doesn't complain anymore,
>>>>>> right?
>>>>>>
>>>>>> Best regards,
>>>>>> baolu
>>>>>>
>>>>>
>>>>> Yes, with the depends it no longer happens.
>>>>
>>>> The dmar code only exists on X86 and IA64 arch's. Adding this depending
>>>> makes sense to me. I will add it if no objections.
>>>
>>> I think that works after Baolu's patchset that makes intel-iommu.h
>>> private.  I'm pretty sure it wouldn't have worked before that.
>>>
>>> No objections.
>>>
>>
>> Yes, I think applying it with the depends prior to Baolu's change would
>> still run into the issue from the KTR report if someone compiled without
>> INTEL_IOMMU enabled.
>>
>> This was dealing with being able to do something like:
>>
>> make allmodconfig ARCH=arm64 ; grep DMAR_UNITS .config
>>
>> and finding CONFIG_DMAR_UNITS_SUPPORTED=64.
>>
>> Thinking some more though, instead of the depends being on the arch
>> would depending on DMAR_TABLE or INTEL_IOMMU be more appropriate?
> 
> At least in my limited exploration, depending on INTEL_IOMMU yields
> compile errors, but depending upon DMAR_TABLE appears to work fine.

DMAR_TABLE is used beyond INTEL_IOMMU, so depending on DMAR_TABLE seems
better.

Steve, do you mind posting a v3 with this fixed?

Best regards,
baolu