linux-kernel - Re: [PATCH v2] iommu/vt-d: Make DMAR_UNITS

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Message-ID: <616dc81c-dfc6-d6c6-1eab-de0e9ba4411f@linux.intel.com>
Date:   Tue, 14 Jun 2022 10:21:29 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jerry Snitselaar <jsnitsel@...hat.com>
Cc:     baolu.lu@...ux.intel.com, Steve Wahl <steve.wahl@....com>,
        Joerg Roedel <jroedel@...e.de>,
        Kyung Min Park <kyung.min.park@...el.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Will Deacon <will@...nel.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Russ Anderson <russ.anderson@....com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] iommu/vt-d: Make DMAR_UNITS_SUPPORTED a config setting

On 2022/6/14 09:54, Jerry Snitselaar wrote:
> On Mon, Jun 13, 2022 at 6:51 PM Baolu Lu <baolu.lu@...ux.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@...ux.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@....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.

Best regards,
baolu