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

[Konrad Rzeszutek Wilk <konrad.wilk-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>]

On Tue, Oct 04, 2016 at 10:00:50AM -0700, Glenn Serre wrote:
> 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.

That ought to be a seperate patch - one functional change per patch (see
Documentation/SubmittingPatches).

Or you can mention this in the commit description..
> 
> 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=