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Mon, 15 Jun 2020 03:02:03 +0000 (UTC) Received: from [10.72.13.232] (ovpn-13-232.pek2.redhat.com [10.72.13.232]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1E19610013D6; Mon, 15 Jun 2020 03:01:56 +0000 (UTC) Subject: Re: [PATCH] s390: protvirt: virtio: Refuse device without IOMMU To: Pierre Morel , linux-kernel@vger.kernel.org Cc: pasic@linux.ibm.com, borntraeger@de.ibm.com, frankja@linux.ibm.com, mst@redhat.com, cohuck@redhat.com, kvm@vger.kernel.org, linux-s390@vger.kernel.org, virtualization@lists.linux-foundation.org References: <1591794711-5915-1-git-send-email-pmorel@linux.ibm.com> <467d5b58-b70c-1c45-4130-76b6e18c05af@redhat.com> <6356ba7f-afab-75e1-05ff-4a22b88c610e@linux.ibm.com> From: Jason Wang Message-ID: Date: Mon, 15 Jun 2020 11:01:55 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <6356ba7f-afab-75e1-05ff-4a22b88c610e@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 >>>> --- >>>>   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 >  #include >  #include > +#include >  #include > >  /* 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 >