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

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Date:   Mon, 13 Jun 2022 18:54:13 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
Cc:     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 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.

Regards,
Jerry