Messages in this thread | | | Subject | Re: [PATCH] s390: protvirt: virtio: Refuse device without IOMMU | From | Jason Wang <> | Date | Mon, 15 Jun 2020 11:01:55 +0800 |
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On 2020/6/12 下午7:38, Pierre Morel wrote: > > > On 2020-06-12 11:21, Pierre Morel wrote: >> >> >> On 2020-06-11 05:10, Jason Wang wrote: >>> >>> On 2020/6/10 下午9:11, Pierre Morel wrote: >>>> Protected Virtualisation protects the memory of the guest and >>>> do not allow a the host to access all of its memory. >>>> >>>> Let's refuse a VIRTIO device which does not use IOMMU >>>> protected access. >>>> >>>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com> >>>> --- >>>> drivers/s390/virtio/virtio_ccw.c | 5 +++++ >>>> 1 file changed, 5 insertions(+) >>>> >>>> diff --git a/drivers/s390/virtio/virtio_ccw.c >>>> b/drivers/s390/virtio/virtio_ccw.c >>>> index 5730572b52cd..06ffbc96587a 100644 >>>> --- a/drivers/s390/virtio/virtio_ccw.c >>>> +++ b/drivers/s390/virtio/virtio_ccw.c >>>> @@ -986,6 +986,11 @@ static void virtio_ccw_set_status(struct >>>> virtio_device *vdev, u8 status) >>>> if (!ccw) >>>> return; >>>> + /* Protected Virtualisation guest needs IOMMU */ >>>> + if (is_prot_virt_guest() && >>>> + !__virtio_test_bit(vdev, VIRTIO_F_IOMMU_PLATFORM)) >>>> + status &= ~VIRTIO_CONFIG_S_FEATURES_OK; >>>> + >>>> /* Write the status to the host. */ >>>> vcdev->dma_area->status = status; >>>> ccw->cmd_code = CCW_CMD_WRITE_STATUS; >>> >>> >>> I wonder whether we need move it to virtio core instead of ccw. >>> >>> I think the other memory protection technologies may suffer from >>> this as well. >>> >>> Thanks >>> >> >> >> What would you think of the following, also taking into account >> Connie's comment on where the test should be done: >> >> - declare a weak function in virtio.c code, returning that memory >> protection is not in use. >> >> - overwrite the function in the arch code >> >> - call this function inside core virtio_finalize_features() and if >> required fail if the device don't have VIRTIO_F_IOMMU_PLATFORM.
I think this is fine.
>> >> Alternative could be to test a global variable that the architecture >> would overwrite if needed but I find the weak function solution more >> flexible. >> >> With a function, we also have the possibility to provide the device >> as argument and take actions depending it, this may answer Halil's >> concern. >> >> Regards, >> Pierre >> > > hum, in between I found another way which seems to me much better: > > We already have the force_dma_unencrypted() function available which > AFAIU is what we want for encrypted memory protection and is already > used by power and x86 SEV/SME in a way that seems AFAIU compatible > with our problem. > > Even DMA and IOMMU are different things, I think they should be used > together in our case. > > What do you think? > > The patch would then be something like: > > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c > index a977e32a88f2..53476d5bbe35 100644 > --- a/drivers/virtio/virtio.c > +++ b/drivers/virtio/virtio.c > @@ -4,6 +4,7 @@ > #include <linux/virtio_config.h> > #include <linux/module.h> > #include <linux/idr.h> > +#include <linux/dma-direct.h> > #include <uapi/linux/virtio_ids.h> > > /* Unique numbering for virtio devices. */ > @@ -179,6 +180,10 @@ int virtio_finalize_features(struct virtio_device > *dev) > if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) > return 0; > > + if (force_dma_unencrypted(&dev->dev) && > + !virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) > + return -EIO; > + > virtio_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK); > status = dev->config->get_status(dev); > if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {
I think this can work but need to listen from Michael.
Thanks
> > > Regards, > Pierre >
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