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

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Date:   Mon, 23 May 2022 06:43:28 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Steve Wahl <steve.wahl@....com>,
        Baolu Lu <baolu.lu@...ux.intel.com>
CC:     Dimitri Sivanich <sivanich@....com>,
        "Rodel, Jorg" <jroedel@...e.de>,
        "Anderson, Russ" <russ.anderson@....com>,
        Mike Travis <mike.travis@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Will Deacon <will@...nel.org>
Subject: RE: [PATCH v2] iommu/vt-d: Make DMAR_UNITS_SUPPORTED a config setting

> From: Steve Wahl
> Sent: Thursday, May 19, 2022 3:58 AM
> 
> On Fri, May 13, 2022 at 10:09:46AM +0800, Baolu Lu wrote:
> > On 2022/5/13 07:12, Steve Wahl 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>
> > >
> > > I've received a report from the kernel test robot <lkp@...el.com>,
> > > that this patch causes an error (shown below) when
> > > CONFIG_IOMMU_SUPPORT is not set.
> > >
> > > In my opinion, this is because include/linux/dmar.h and
> > > include/linux/intel-iommu are being #included when they are not really
> > > being used.
> > >
> > > I've tried placing the contents of intel-iommu.h within an #ifdef
> > > CONFIG_INTEL_IOMMU, and that fixes the problem.
> > >
> > > Two questions:
> > >
> > > A) Is this the desired approach to to the fix?
> >
> > Most part of include/linux/intel-iommu.h is private to Intel IOMMU
> > driver. They should be put in a header like drivers/iommu/intel
> > /iommu.h. Eventually, we should remove include/linux/intel-iommu.h
> > and device drivers interact with iommu subsystem through the IOMMU
> > kAPIs.
> >
> > Best regards,
> > baolu
> 
> Baolu's recent patch to move intel-iommu.h private still allows my
> [PATCH v2] to apply with no changes, and gets rid of the compile
> errors when CONFIG_IOMMU_SUPPORT is not set, so the kernel test robot
> should be happy now.
> 
> Is there another step I should do to bring this patch back into focus?
> 

This looks good to me.

Reviewed-by: Kevin Tian <kevin.tian@...el.com>