Re: [PATCH] vfio: Depend on MMU

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Mar 08, 2021 at 07:14:21PM +0100, Cornelia Huck wrote:
> On Fri, 5 Mar 2021 19:11:41 -0400
> Jason Gunthorpe <jgg@nvidia.com> wrote:
> 
> > On Fri, Mar 05, 2021 at 09:46:49AM +0100, Cornelia Huck wrote:
> > > On Thu, 4 Mar 2021 21:30:03 -0400
> > > Jason Gunthorpe <jgg@nvidia.com> wrote:
> > >   
> > > > VFIO_IOMMU_TYPE1 does not compile with !MMU:
> > > > 
> > > > ../drivers/vfio/vfio_iommu_type1.c: In function 'follow_fault_pfn':
> > > > ../drivers/vfio/vfio_iommu_type1.c:536:22: error: implicit declaration of function 'pte_write'; did you mean 'vfs_write'? [-Werror=implicit-function-declaration]
> > > > 
> > > > So require it.
> > > > 
> > > > Suggested-by: Cornelia Huck <cohuck@redhat.com>
> > > > Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> > > >  drivers/vfio/Kconfig | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig
> > > > index 90c0525b1e0cf4..67d0bf4efa1606 100644
> > > > +++ b/drivers/vfio/Kconfig
> > > > @@ -22,7 +22,7 @@ config VFIO_VIRQFD
> > > >  menuconfig VFIO
> > > >  	tristate "VFIO Non-Privileged userspace driver framework"
> > > >  	select IOMMU_API
> > > > -	select VFIO_IOMMU_TYPE1 if (X86 || S390 || ARM || ARM64)
> > > > +	select VFIO_IOMMU_TYPE1 if MMU && (X86 || S390 || ARM || ARM64)
> > > >  	help
> > > >  	  VFIO provides a framework for secure userspace device drivers.
> > > >  	  See Documentation/driver-api/vfio.rst for more details.  
> > > 
> > > Actually, I'm wondering how much sense vfio makes on !MMU at all? (And
> > > maybe just merge this with your patch that switches IOMMU_API from a
> > > depend to a select, because that is the change that makes the MMU
> > > dependency required?)  
> > 
> > Why does changing depend to select affect MMU vs !MMU? Am I missing
> > something?
> > 
> > It looks like IOMMU_API can be turned with ARM !MMU here, for
> > instance:
> > 
> > config MSM_IOMMU
> >         bool "MSM IOMMU Support"
> >         depends on ARM
> >         depends on ARCH_MSM8X60 || ARCH_MSM8960 || COMPILE_TEST
> >         select IOMMU_API
> 
> But that one is sitting under a menu depending on MMU, isn't it?

Yep.

Still, I'd keep the two ideas as two patches - order this one first.

Jason