From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:58540 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725805AbgFLLi0 (ORCPT ); Fri, 12 Jun 2020 07:38:26 -0400 Subject: Re: [PATCH] s390: protvirt: virtio: Refuse device without IOMMU From: Pierre Morel References: <1591794711-5915-1-git-send-email-pmorel@linux.ibm.com> <467d5b58-b70c-1c45-4130-76b6e18c05af@redhat.com> Message-ID: <6356ba7f-afab-75e1-05ff-4a22b88c610e@linux.ibm.com> Date: Fri, 12 Jun 2020 13:38:17 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format="flowed" Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-s390-owner@vger.kernel.org List-ID: To: Jason Wang , 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 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. > > 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)) { Regards, Pierre -- Pierre Morel IBM Lab Boeblingen