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bh=fgNAe0kFX8jwOB1IGnADdVWTUeU+aOcqCkGioFUGvME=; b=TiWTHwfwkliu0zdRzwy9LSgU2fxE8jvM5RO8mTyOyTt6QbJeRl4zHqlp+aewiwlRq0Yebg Cn64BOsYL8/N/CL/GbQHqMsZoc5miUhc3lamwCWsTnzIjeGUImlkmRz2tiXDDxtlmWD4mF I5+8jO6JPWi/rKU0MhtALiIi9rln8nY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-330-uzZvj-nxM0uyMHF_EGtW_Q-1; Fri, 03 Apr 2020 11:34:44 -0400 X-MC-Unique: uzZvj-nxM0uyMHF_EGtW_Q-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E9E90800D50; Fri, 3 Apr 2020 15:34:42 +0000 (UTC) Received: from w520.home (ovpn-112-162.phx2.redhat.com [10.3.112.162]) by smtp.corp.redhat.com (Postfix) with ESMTP id 92087A0A7B; Fri, 3 Apr 2020 15:34:36 +0000 (UTC) Date: Fri, 3 Apr 2020 09:34:36 -0600 From: Alex Williamson To: "Tian, Kevin" Subject: Re: [PATCH v1 7/8] vfio/type1: Add VFIO_IOMMU_CACHE_INVALIDATE Message-ID: <20200403093436.094b1928@w520.home> In-Reply-To: References: <1584880325-10561-1-git-send-email-yi.l.liu@intel.com> <1584880325-10561-8-git-send-email-yi.l.liu@intel.com> <20200402142428.2901432e@w520.home> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Cc: "jean-philippe@linaro.org" , "Raj, Ashok" , "kvm@vger.kernel.org" , "Tian, Jun J" , "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" , "Sun, Yi Y" , "Wu, Hao" X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Fri, 3 Apr 2020 06:39:22 +0000 "Tian, Kevin" wrote: > > From: Alex Williamson > > Sent: Friday, April 3, 2020 4:24 AM > > > > On Sun, 22 Mar 2020 05:32:04 -0700 > > "Liu, Yi L" wrote: > > > > > From: Liu Yi L > > > > > > For VFIO IOMMUs with the type VFIO_TYPE1_NESTING_IOMMU, guest > > "owns" the > > > first-level/stage-1 translation structures, the host IOMMU driver has no > > > knowledge of first-level/stage-1 structure cache updates unless the guest > > > invalidation requests are trapped and propagated to the host. > > > > > > This patch adds a new IOCTL VFIO_IOMMU_CACHE_INVALIDATE to > > propagate guest > > > first-level/stage-1 IOMMU cache invalidations to host to ensure IOMMU > > cache > > > correctness. > > > > > > With this patch, vSVA (Virtual Shared Virtual Addressing) can be used safely > > > as the host IOMMU iotlb correctness are ensured. > > > > > > Cc: Kevin Tian > > > CC: Jacob Pan > > > Cc: Alex Williamson > > > Cc: Eric Auger > > > Cc: Jean-Philippe Brucker > > > Signed-off-by: Liu Yi L > > > Signed-off-by: Eric Auger > > > Signed-off-by: Jacob Pan > > > --- > > > drivers/vfio/vfio_iommu_type1.c | 49 > > +++++++++++++++++++++++++++++++++++++++++ > > > include/uapi/linux/vfio.h | 22 ++++++++++++++++++ > > > 2 files changed, 71 insertions(+) > > > > > > diff --git a/drivers/vfio/vfio_iommu_type1.c > > b/drivers/vfio/vfio_iommu_type1.c > > > index a877747..937ec3f 100644 > > > --- a/drivers/vfio/vfio_iommu_type1.c > > > +++ b/drivers/vfio/vfio_iommu_type1.c > > > @@ -2423,6 +2423,15 @@ static long > > vfio_iommu_type1_unbind_gpasid(struct vfio_iommu *iommu, > > > return ret; > > > } > > > > > > +static int vfio_cache_inv_fn(struct device *dev, void *data) > > > +{ > > > + struct domain_capsule *dc = (struct domain_capsule *)data; > > > + struct iommu_cache_invalidate_info *cache_inv_info = > > > + (struct iommu_cache_invalidate_info *) dc->data; > > > + > > > + return iommu_cache_invalidate(dc->domain, dev, cache_inv_info); > > > +} > > > + > > > static long vfio_iommu_type1_ioctl(void *iommu_data, > > > unsigned int cmd, unsigned long arg) > > > { > > > @@ -2629,6 +2638,46 @@ static long vfio_iommu_type1_ioctl(void > > *iommu_data, > > > } > > > kfree(gbind_data); > > > return ret; > > > + } else if (cmd == VFIO_IOMMU_CACHE_INVALIDATE) { > > > + struct vfio_iommu_type1_cache_invalidate cache_inv; > > > + u32 version; > > > + int info_size; > > > + void *cache_info; > > > + int ret; > > > + > > > + minsz = offsetofend(struct > > vfio_iommu_type1_cache_invalidate, > > > + flags); > > > > This breaks backward compatibility as soon as struct > > iommu_cache_invalidate_info changes size by its defined versioning > > scheme. ie. a field gets added, the version is bumped, all existing > > userspace breaks. Our minsz is offsetofend to the version field, > > interpret the version to size, then reevaluate argsz. > > btw the version scheme is challenged by Christoph Hellwig. After > some discussions, we need your guidance how to move forward. > Jacob summarized available options below: > https://lkml.org/lkml/2020/4/2/876 Ok > > > > > + > > > + if (copy_from_user(&cache_inv, (void __user *)arg, minsz)) > > > + return -EFAULT; > > > + > > > + if (cache_inv.argsz < minsz || cache_inv.flags) > > > + return -EINVAL; > > > + > > > + /* Get the version of struct iommu_cache_invalidate_info */ > > > + if (copy_from_user(&version, > > > + (void __user *) (arg + minsz), sizeof(version))) > > > + return -EFAULT; > > > + > > > + info_size = iommu_uapi_get_data_size( > > > + IOMMU_UAPI_CACHE_INVAL, > > version); > > > + > > > + cache_info = kzalloc(info_size, GFP_KERNEL); > > > + if (!cache_info) > > > + return -ENOMEM; > > > + > > > + if (copy_from_user(cache_info, > > > + (void __user *) (arg + minsz), info_size)) { > > > + kfree(cache_info); > > > + return -EFAULT; > > > + } > > > + > > > + mutex_lock(&iommu->lock); > > > + ret = vfio_iommu_for_each_dev(iommu, vfio_cache_inv_fn, > > > + cache_info); > > > > How does a user respond when their cache invalidate fails? Isn't this > > also another case where our for_each_dev can fail at an arbitrary point > > leaving us with no idea whether each device even had the opportunity to > > perform the invalidation request. I don't see how we have any chance > > to maintain coherency after this faults. > > Then can we make it simple to support singleton group only? Are you suggesting a single group per container or a single device per group? Unless we have both, aren't we always going to have this issue. OTOH, why should a cache invalidate fail? > > > + mutex_unlock(&iommu->lock); > > > + kfree(cache_info); > > > + return ret; > > > } > > > > > > return -ENOTTY; > > > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h > > > index 2235bc6..62ca791 100644 > > > --- a/include/uapi/linux/vfio.h > > > +++ b/include/uapi/linux/vfio.h > > > @@ -899,6 +899,28 @@ struct vfio_iommu_type1_bind { > > > */ > > > #define VFIO_IOMMU_BIND _IO(VFIO_TYPE, VFIO_BASE + 23) > > > > > > +/** > > > + * VFIO_IOMMU_CACHE_INVALIDATE - _IOW(VFIO_TYPE, VFIO_BASE + 24, > > > + * struct vfio_iommu_type1_cache_invalidate) > > > + * > > > + * Propagate guest IOMMU cache invalidation to the host. The cache > > > + * invalidation information is conveyed by @cache_info, the content > > > + * format would be structures defined in uapi/linux/iommu.h. User > > > + * should be aware of that the struct iommu_cache_invalidate_info > > > + * has a @version field, vfio needs to parse this field before getting > > > + * data from userspace. > > > + * > > > + * Availability of this IOCTL is after VFIO_SET_IOMMU. > > > > Is this a necessary qualifier? A user can try to call this ioctl at > > any point, it only makes sense in certain configurations, but it should > > always "do the right thing" relative to the container iommu config. > > > > Also, I don't see anything in these last few patches testing the > > operating IOMMU model, what happens when a user calls them when not > > using the nesting IOMMU? > > > > Is this ioctl and the previous BIND ioctl only valid when configured > > for the nesting IOMMU type? > > I think so. We should add the nesting check in those new ioctls. > > > > > > + * > > > + * returns: 0 on success, -errno on failure. > > > + */ > > > +struct vfio_iommu_type1_cache_invalidate { > > > + __u32 argsz; > > > + __u32 flags; > > > + struct iommu_cache_invalidate_info cache_info; > > > +}; > > > +#define VFIO_IOMMU_CACHE_INVALIDATE _IO(VFIO_TYPE, VFIO_BASE > > + 24) > > > > The future extension capabilities of this ioctl worry me, I wonder if > > we should do another data[] with flag defining that data as CACHE_INFO. > > Can you elaborate? Does it mean with this way we don't rely on iommu > driver to provide version_to_size conversion and instead we just pass > data[] to iommu driver for further audit? No, my concern is that this ioctl has a single function, strictly tied to the iommu uapi. If we replace cache_info with data[] then we can define a flag to specify that data[] is struct iommu_cache_invalidate_info, and if we need to, a different flag to identify data[] as something else. For example if we get stuck expanding cache_info to meet new demands and develop a new uapi to solve that, how would we expand this ioctl to support it rather than also create a new ioctl? There's also a trade-off in making the ioctl usage more difficult for the user. I'd still expect the vfio layer to check the flag and interpret data[] as indicated by the flag rather than just passing a blob of opaque data to the iommu layer though. Thanks, Alex _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu