Messages in this thread | | | Subject | Re: [PATCH v2 1/1] s390: virtio: let arch accept devices without IOMMU feature | From | Pierre Morel <> | Date | Tue, 16 Jun 2020 12:52:50 +0200 |
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On 2020-06-16 11:52, Halil Pasic wrote: > On Mon, 15 Jun 2020 14:39:24 +0200 > Pierre Morel <pmorel@linux.ibm.com> wrote: > > I find the subject (commit short) sub optimal. The 'arch' is already > accepting devices 'without IOMMU feature'. What you are introducing is > the ability to reject. > >> An architecture protecting the guest memory against unauthorized host >> access may want to enforce VIRTIO I/O device protection through the >> use of VIRTIO_F_IOMMU_PLATFORM. >> >> Let's give a chance to the architecture to accept or not devices >> without VIRTIO_F_IOMMU_PLATFORM. >> > > I don't particularly like the commit message. In general, I believe > using access_platform instead of iommu_platform would really benefit us.
IOMMU_PLATFORM is used overall in Linux, and I did not find any occurrence for ACCESS_PLATFORM.
> >> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com> >> --- >> arch/s390/mm/init.c | 6 ++++++ >> drivers/virtio/virtio.c | 9 +++++++++ >> include/linux/virtio.h | 2 ++ >> 3 files changed, 17 insertions(+) >> >> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c >> index 87b2d024e75a..3f04ad09650f 100644 >> --- a/arch/s390/mm/init.c >> +++ b/arch/s390/mm/init.c >> @@ -46,6 +46,7 @@ >> #include <asm/kasan.h> >> #include <asm/dma-mapping.h> >> #include <asm/uv.h> >> +#include <linux/virtio.h> > > arch/s390/mm/init.c including virtio.h looks a bit strange to me, but > if Heiko and Vasily don't mind, neither do I.
Do we have a better place to install the hook? I though that since it is related to memory management and that, since force_dma_unencrypted already is there, it would be a good place.
However, kvm-s390 is another candidate.
> >> >> pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir); >> >> @@ -162,6 +163,11 @@ bool force_dma_unencrypted(struct device *dev) >> return is_prot_virt_guest(); >> } >> >> +int arch_needs_iommu_platform(struct virtio_device *dev) > > Maybe prefixing the name with virtio_ would help provide the > proper context.
The virtio_dev makes it obvious and from the virtio side it should be obvious that the arch is responsible for this.
However if nobody has something against I change it.
> >> +{ >> + return is_prot_virt_guest(); >> +} >> + >> /* protected virtualization */ >> static void pv_init(void) >> { >> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c >> index a977e32a88f2..30091089bee8 100644 >> --- a/drivers/virtio/virtio.c >> +++ b/drivers/virtio/virtio.c >> @@ -167,6 +167,11 @@ void virtio_add_status(struct virtio_device *dev, unsigned int status) >> } >> EXPORT_SYMBOL_GPL(virtio_add_status); >> >> +int __weak arch_needs_iommu_platform(struct virtio_device *dev) >> +{ >> + return 0; >> +} >> + > > Adding some people that could be interested in overriding this as well > to the cc list.
Thanks,
> >> int virtio_finalize_features(struct virtio_device *dev) >> { >> int ret = dev->config->finalize_features(dev); >> @@ -179,6 +184,10 @@ int virtio_finalize_features(struct virtio_device *dev) >> if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) >> return 0; >> >> + if (arch_needs_iommu_platform(dev) && >> + !virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) >> + return -EIO; >> + > > Why EIO?
Because I/O can not occur correctly? I am open to suggestions.
> > Overall, I think it is a good idea to have something that is going to > protect us from this scenario. >
It would clearly be a good thing that trusted hypervizors like QEMU forbid this scenario however should we let the door open?
Thanks, Pierre
-- Pierre Morel IBM Lab Boeblingen
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