RE: [PATCH v6 17/18] vfio/type1: Check MSI remapping at irq domain level

[Bharat Bhushan]

> -----Original Message-----
> From: Marc Zyngier [mailto:marc.zyngier@xxxxxxx]
> Sent: Friday, January 06, 2017 2:50 PM
> To: Auger Eric <eric.auger@xxxxxxxxxx>; Bharat Bhushan
> <bharat.bhushan@xxxxxxx>; eric.auger.pro@xxxxxxxxx;
> christoffer.dall@xxxxxxxxxx; robin.murphy@xxxxxxx;
> alex.williamson@xxxxxxxxxx; will.deacon@xxxxxxx; joro@xxxxxxxxxx;
> tglx@xxxxxxxxxxxxx; jason@xxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx
> Cc: kvm@xxxxxxxxxxxxxxx; drjones@xxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; pranav.sawargaonkar@xxxxxxxxx;
> iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; punit.agrawal@xxxxxxx; Diana Madalina
> Craciun <diana.craciun@xxxxxxx>; gpkulkarni@xxxxxxxxx;
> shankerd@xxxxxxxxxxxxxx; geethasowjanya.akula@xxxxxxxxx
> Subject: Re: [PATCH v6 17/18] vfio/type1: Check MSI remapping at irq
> domain level
> 
> On 06/01/17 09:08, Auger Eric wrote:
> > Hi Bharat
> >
> > On 06/01/2017 09:50, Bharat Bhushan wrote:
> >> Hi Eric,
> >>
> >>> -----Original Message-----
> >>> From: Eric Auger [mailto:eric.auger@xxxxxxxxxx]
> >>> Sent: Friday, January 06, 2017 12:35 AM
> >>> To: eric.auger@xxxxxxxxxx; eric.auger.pro@xxxxxxxxx;
> >>> christoffer.dall@xxxxxxxxxx; marc.zyngier@xxxxxxx;
> >>> robin.murphy@xxxxxxx; alex.williamson@xxxxxxxxxx;
> >>> will.deacon@xxxxxxx; joro@xxxxxxxxxx; tglx@xxxxxxxxxxxxx;
> >>> jason@xxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> >>> Cc: kvm@xxxxxxxxxxxxxxx; drjones@xxxxxxxxxx; linux-
> >>> kernel@xxxxxxxxxxxxxxx; pranav.sawargaonkar@xxxxxxxxx;
> >>> iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; punit.agrawal@xxxxxxx; Diana
> >>> Madalina Craciun <diana.craciun@xxxxxxx>; gpkulkarni@xxxxxxxxx;
> >>> shankerd@xxxxxxxxxxxxxx; Bharat Bhushan
> <bharat.bhushan@xxxxxxx>;
> >>> geethasowjanya.akula@xxxxxxxxx
> >>> Subject: [PATCH v6 17/18] vfio/type1: Check MSI remapping at irq
> >>> domain level
> >>>
> >>> In case the IOMMU translates MSI transactions (typical case on ARM),
> >>> we check MSI remapping capability at IRQ domain level. Otherwise it
> >>> is checked at IOMMU level.
> >>>
> >>> At this stage the arm-smmu-(v3) still advertise the
> >>> IOMMU_CAP_INTR_REMAP capability at IOMMU level. This will be
> removed
> >>> in subsequent patches.
> >>>
> >>> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
> >>>
> >>> ---
> >>>
> >>> v6: rewrite test
> >>> ---
> >>>  drivers/vfio/vfio_iommu_type1.c | 9 ++++++---
> >>>  1 file changed, 6 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/drivers/vfio/vfio_iommu_type1.c
> >>> b/drivers/vfio/vfio_iommu_type1.c index b473ef80..fa0b5c4 100644
> >>> --- a/drivers/vfio/vfio_iommu_type1.c
> >>> +++ b/drivers/vfio/vfio_iommu_type1.c
> >>> @@ -40,6 +40,7 @@
> >>>  #include <linux/mdev.h>
> >>>  #include <linux/notifier.h>
> >>>  #include <linux/dma-iommu.h>
> >>> +#include <linux/irqdomain.h>
> >>>
> >>>  #define DRIVER_VERSION  "0.2"
> >>>  #define DRIVER_AUTHOR   "Alex Williamson
> >>> <alex.williamson@xxxxxxxxxx>"
> >>> @@ -1208,7 +1209,7 @@ static int
> vfio_iommu_type1_attach_group(void
> >>> *iommu_data,
> >>>  	struct vfio_domain *domain, *d;
> >>>  	struct bus_type *bus = NULL, *mdev_bus;
> >>>  	int ret;
> >>> -	bool resv_msi;
> >>> +	bool resv_msi, msi_remap;
> >>>  	phys_addr_t resv_msi_base;
> >>>
> >>>  	mutex_lock(&iommu->lock);
> >>> @@ -1284,8 +1285,10 @@ static int
> vfio_iommu_type1_attach_group(void
> >>> *iommu_data,
> >>>  	INIT_LIST_HEAD(&domain->group_list);
> >>>  	list_add(&group->next, &domain->group_list);
> >>>
> >>> -	if (!allow_unsafe_interrupts &&
> >>> -	    !iommu_capable(bus, IOMMU_CAP_INTR_REMAP)) {
> >>> +	msi_remap = resv_msi ? irq_domain_check_msi_remap() :
> >>
> >> There can be multiple interrupt-controller, at-least theoretically it is
> possible and not sure practically it exists and supported, where not all may
> support IRQ_REMAP. If that is the case be then should we check for IRQ-
> REMAP for that device-bus irq-domain?
> >>
> > I mentioned in the cover letter that the approach was defensive and
> > rough today. As soon as we detect an MSI controller in the platform
> > that has no support for MSI remapping we flag the assignment as
> > unsafe. I think this approach was agreed on the ML. Such rough
> > assessment was used in the past on x86.
> >
> > I am reluctant to add more complexity at that stage. This can be
> > improved latter I think when such platforms show up.
> 
> I don't think this is worth it. If the system is so broken that the designer
> cannot make up their mind about device isolation, too bad.
> People will either disable the non-isolating MSI controller altogether, or force
> the unsafe flag.

Understand, just want to be sure that this is a known limitation. It will be good if we have some comment around this function.

Thanks
-Bharat

> 
> Thanks,
> 
> 	M.
> --
> Jazz is not dead. It just smells funny...