Re: [PATCH v1 1/1] arch/x86: Add CONFIG_IOMMU_DEFAULT_PT for iommu=pt

[Glenn Serre <gserre-43mecJUBy8ZBDgjK7y7TUQ@public.gmane.org>]

Good afternoon,

On 10/04/2016 09:52 AM, Konrad Rzeszutek Wilk wrote:
> On Tue, Oct 04, 2016 at 09:11:39AM -0700, Glenn Serre wrote:
>> Add CONFIG_IOMMU_DEFAULT_PT for iommu=pt
>>
>> Allow default to iommu=pt without adding to command line.
>> Add iommu=nopt to turn off default.
>>
>> The reason we use iommu=pt is to support using the DPDK igb_uio driver,
>> which we need to do on servers that have an iommu but lack ACS.
>>
>> Signed-off-by: Glenn Serre <gserre-43mecJUBy8ZBDgjK7y7TUQ@public.gmane.org>
>> ---
>>  Documentation/kernel-parameters.txt | 3 ++-
>>  arch/x86/Kconfig                    | 7 +++++++
>>  arch/x86/kernel/pci-dma.c           | 6 ++++++
>>  3 files changed, 15 insertions(+), 1 deletion(-)
>>
>> --- a/Documentation/kernel-parameters.txt
>> +++ b/Documentation/kernel-parameters.txt
>> @@ -1607,7 +1607,8 @@
>>  		nomerge
>>  		forcesac
>>  		soft
>> -		pt		[x86, IA-64]
>> +		pt		[x86]
>
> What about adding IA-64 back on?

As far as I can see, IA-64 doesn't pay any attention at all to the iommu 
parameter.  In arch/ia64/kernel/pci-dma.c, I see

int iommu_pass_through;

but no early_param("iommu"), other occurrence of "iommu", or reference to 
iommu_pass_through.

Thanks,
--Glenn S.

>
>> +		nopt		[x86]
>
> Or here?
>>  		nobypass	[PPC/POWERNV]
>>  			Disable IOMMU bypass, using IOMMU for PCI devices.
>>
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -845,6 +845,13 @@
>>  	def_bool y
>>  	depends on CALGARY_IOMMU || GART_IOMMU || SWIOTLB || AMD_IOMMU
>>
>> +config IOMMU_DEFAULT_PT
>> +	def_bool n
>> +	prompt "Set iommu=pt by default"
>> +	help
>> +	  Selecting this option will set iommu passthrough (iommu=pt)
>> +	  by default.  Use iommu=nopt to override.
>> +
>>  config MAXSMP
>>  	bool "Enable Maximum number of SMP Processors and NUMA Nodes"
>>  	depends on X86_64 && SMP && DEBUG_KERNEL
>> --- a/arch/x86/kernel/pci-dma.c
>> +++ b/arch/x86/kernel/pci-dma.c
>> @@ -43,7 +43,7 @@
>>   * useful if a user wants to use an IOMMU only for KVM device assignment to
>>   * guests and not for driver dma translation.
>>   */
>> -int iommu_pass_through __read_mostly;
>> +int iommu_pass_through __read_mostly = IS_ENABLED(CONFIG_IOMMU_DEFAULT_PT);
>>
>>  extern struct iommu_table_entry __iommu_table[], __iommu_table_end[];
>>
>> @@ -196,6 +196,8 @@
>>  #endif
>>  		if (!strncmp(p, "pt", 2))
>>  			iommu_pass_through = 1;
>> +		if (!strncmp(p, "nopt", 4))
>> +			iommu_pass_through = 0;
>>
>>  		gart_parse_options(p);
>>
>> _______________________________________________
>> iommu mailing list
>> iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.linuxfoundation.org_mailman_listinfo_iommu&d=DQIBAg&c=IL_XqQWOjubgfqINi2jTzg&r=3biwyMBB1JD9rm0R5wqz7zcDVkNif9HJ5Pflrr18dkw&m=sJQfEY5rZcAq-0QEyNvDxZkeujsoeiY8B_gabGOkyv8&s=ctQKeFfmQJ0ET8hJNBJmeRxdv_gwYgvysgku7sxdV4o&e=