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

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Message-ID: <9c943703-0c2f-b654-a28b-f594bf90bec9@linux.intel.com>
Date:   Tue, 14 Jun 2022 09:51:08 +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 09:44, 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