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

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Date:   Fri, 13 May 2022 10:09:46 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Steve Wahl <steve.wahl@....com>, Joerg Roedel <jroedel@...e.de>,
        David Woodhouse <dwmw2@...radead.org>,
        Will Deacon <will@...nel.org>, iommu@...ts.linux-foundation.org
Cc:     baolu.lu@...ux.intel.com, Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Russ Anderson <russ.anderson@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iommu/vt-d: Make DMAR_UNITS_SUPPORTED a config setting

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

> 
> B) Should it be a separate patch, or added onto this patch as a v3?
> 
> Error message:  ------------------------------
> 
>     In file included from include/linux/intel-iommu.h:21,
>                      from arch/x86/kvm/x86.c:44:
>>> include/linux/dmar.h:21:33: error: 'CONFIG_DMAR_UNITS_SUPPORTED' undeclared here (not in a function); did you mean 'DMAR_UNITS_SUPPORTED'?
>        21 | #define DMAR_UNITS_SUPPORTED    CONFIG_DMAR_UNITS_SUPPORTED
>           |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>     include/linux/intel-iommu.h:531:35: note: in expansion of macro 'DMAR_UNITS_SUPPORTED'
>       531 |         unsigned int iommu_refcnt[DMAR_UNITS_SUPPORTED];
>           |                                   ^~~~~~~~~~~~~~~~~~~~
> 
> 
> vim +21 include/linux/dmar.h
> 
>      20
>    > 21  #define DMAR_UNITS_SUPPORTED    CONFIG_DMAR_UNITS_SUPPORTED
>      22
> 
> Initial stab at fixing it: ------------------------------
> 
> diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
> index 2f9891cb3d00..916fd7b5bcb5 100644
> --- a/include/linux/intel-iommu.h
> +++ b/include/linux/intel-iommu.h
> @@ -10,6 +10,8 @@
>   #ifndef _INTEL_IOMMU_H_
>   #define _INTEL_IOMMU_H_
>   
> +#ifdef CONFIG_INTEL_IOMMU
> +
>   #include <linux/types.h>
>   #include <linux/iova.h>
>   #include <linux/io.h>
> @@ -831,4 +833,6 @@ static inline const char *decode_prq_descriptor(char *str, size_t size,
>   	return str;
>   }
>   
> +#endif /* CONFIG_IOMMU_SUPPORT */
> +
>   #endif
> 
> 
> Thanks.
> 
> --> Steve Wahl
> 
>