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[5.90.115.88]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-427d2a53ccfsm143632605e9.11.2024.07.22.00.50.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Jul 2024 00:50:58 -0700 (PDT) Date: Mon, 22 Jul 2024 03:50:56 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: Srujana Challa , "virtualization@lists.linux.dev" , "kvm@vger.kernel.org" , Vamsi Krishna Attunuru , Shijith Thotton , Nithin Kumar Dabilpuram , Jerin Jacob , "joro@8bytes.org" , "will@kernel.org" Subject: Re: [EXTERNAL] Re: [PATCH] vdpa: Add support for no-IOMMU mode Message-ID: <20240722034957-mutt-send-email-mst@kernel.org> References: <20240530101823.1210161-1-schalla@marvell.com> <20240717054547-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit On Mon, Jul 22, 2024 at 03:22:22PM +0800, Jason Wang wrote: > On Fri, Jul 19, 2024 at 11:40 PM Srujana Challa wrote: > > > > > On Thu, May 30, 2024 at 03:48:23PM +0530, Srujana Challa wrote: > > > > This commit introduces support for an UNSAFE, no-IOMMU mode in the > > > > vhost-vdpa driver. When enabled, this mode provides no device > > > > isolation, no DMA translation, no host kernel protection, and cannot > > > > be used for device assignment to virtual machines. It requires RAWIO > > > > permissions and will taint the kernel. > > > > This mode requires enabling the > > > "enable_vhost_vdpa_unsafe_noiommu_mode" > > > > option on the vhost-vdpa driver. This mode would be useful to get > > > > better performance on specifice low end machines and can be leveraged > > > > by embedded platforms where applications run in controlled environment. > > > > > > > > Signed-off-by: Srujana Challa > > > > > > Thought hard about that. > > > I think given vfio supports this, we can do that too, and the extension is small. > > > > > > However, it looks like setting this parameter will automatically change the > > > behaviour for existing userspace when IOMMU_DOMAIN_IDENTITY is set. > > > > > > I suggest a new domain type for use just for this purpose. > > I'm not sure I get this, we want to bypass IOMMU, so it doesn't even > have a doman. yes, a fake one. or come up with some other flag that userspace will set. > > This way if host has > > > an iommu, then the same kernel can run both VMs with isolation and unsafe > > > embedded apps without. > > Could you provide further details on this concept? What criteria would determine > > the configuration of the new domain type? Would this require a boot parameter > > similar to IOMMU_DOMAIN_IDENTITY, such as iommu.passthrough=1 or iommu.pt? > > Thanks > > > > > > > > --- > > > > drivers/vhost/vdpa.c | 23 +++++++++++++++++++++++ > > > > 1 file changed, 23 insertions(+) > > > > > > > > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c index > > > > bc4a51e4638b..d071c30125aa 100644 > > > > --- a/drivers/vhost/vdpa.c > > > > +++ b/drivers/vhost/vdpa.c > > > > @@ -36,6 +36,11 @@ enum { > > > > > > > > #define VHOST_VDPA_IOTLB_BUCKETS 16 > > > > > > > > +bool vhost_vdpa_noiommu; > > > > +module_param_named(enable_vhost_vdpa_unsafe_noiommu_mode, > > > > + vhost_vdpa_noiommu, bool, 0644); > > > > +MODULE_PARM_DESC(enable_vhost_vdpa_unsafe_noiommu_mode, > > > "Enable > > > > +UNSAFE, no-IOMMU mode. This mode provides no device isolation, no > > > > +DMA translation, no host kernel protection, cannot be used for device > > > > +assignment to virtual machines, requires RAWIO permissions, and will > > > > +taint the kernel. If you do not know what this is for, step away. > > > > +(default: false)"); > > > > + > > > > struct vhost_vdpa_as { > > > > struct hlist_node hash_link; > > > > struct vhost_iotlb iotlb; > > > > @@ -60,6 +65,7 @@ struct vhost_vdpa { > > > > struct vdpa_iova_range range; > > > > u32 batch_asid; > > > > bool suspended; > > > > + bool noiommu_en; > > > > }; > > > > > > > > static DEFINE_IDA(vhost_vdpa_ida); > > > > @@ -887,6 +893,10 @@ static void vhost_vdpa_general_unmap(struct > > > > vhost_vdpa *v, { > > > > struct vdpa_device *vdpa = v->vdpa; > > > > const struct vdpa_config_ops *ops = vdpa->config; > > > > + > > > > + if (v->noiommu_en) > > > > + return; > > > > + > > > > if (ops->dma_map) { > > > > ops->dma_unmap(vdpa, asid, map->start, map->size); > > > > } else if (ops->set_map == NULL) { > > > > @@ -980,6 +990,9 @@ static int vhost_vdpa_map(struct vhost_vdpa *v, > > > struct vhost_iotlb *iotlb, > > > > if (r) > > > > return r; > > > > > > > > + if (v->noiommu_en) > > > > + goto skip_map; > > > > + > > > > if (ops->dma_map) { > > > > r = ops->dma_map(vdpa, asid, iova, size, pa, perm, opaque); > > > > } else if (ops->set_map) { > > > > @@ -995,6 +1008,7 @@ static int vhost_vdpa_map(struct vhost_vdpa *v, > > > struct vhost_iotlb *iotlb, > > > > return r; > > > > } > > > > > > > > +skip_map: > > > > if (!vdpa->use_va) > > > > atomic64_add(PFN_DOWN(size), &dev->mm->pinned_vm); > > > > > > > > @@ -1298,6 +1312,7 @@ static int vhost_vdpa_alloc_domain(struct > > > vhost_vdpa *v) > > > > struct vdpa_device *vdpa = v->vdpa; > > > > const struct vdpa_config_ops *ops = vdpa->config; > > > > struct device *dma_dev = vdpa_get_dma_dev(vdpa); > > > > + struct iommu_domain *domain; > > > > const struct bus_type *bus; > > > > int ret; > > > > > > > > @@ -1305,6 +1320,14 @@ static int vhost_vdpa_alloc_domain(struct > > > vhost_vdpa *v) > > > > if (ops->set_map || ops->dma_map) > > > > return 0; > > > > > > > > + domain = iommu_get_domain_for_dev(dma_dev); > > > > + if ((!domain || domain->type == IOMMU_DOMAIN_IDENTITY) && > > > > + vhost_vdpa_noiommu && capable(CAP_SYS_RAWIO)) { > > > > > > So if userspace does not have CAP_SYS_RAWIO instead of failing with a > > > permission error the functionality changes silently? > > > That's confusing, I think. > > Yes, you are correct. I will modify the code to return error when vhost_vdpa_noiommu > > is set and CAP_SYS_RAWIO is not set. > > > > Thanks. > > > > > > > > > > + add_taint(TAINT_USER, LOCKDEP_STILL_OK); > > > > + dev_warn(&v->dev, "Adding kernel taint for noiommu on > > > device\n"); > > > > + v->noiommu_en = true; > > > > + return 0; > > > > + } > > > > bus = dma_dev->bus; > > > > if (!bus) > > > > return -EFAULT; > > > > -- > > > > 2.25.1 > >