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bh=tw6YcOdTb57tTJEpjUT4XTUayFnAW1S4FhIT3XPkFRo=; b=GwdTQEjh0Twb1OtQSEToA2Sl7KYqm7imxTSHLOS1ZSIf5hcNtyfWFYin2p782QDaoxLcLB w/nogAGUF7rW9t4u6dW9z6pkJUIDGCdJW8dOrr3NBHjtZfYzFHk+KuUNYxXbnTLuXgDjRr F1eJ2SWm9KViW2cfHEiytKG1sOKpnjk= 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-13-bmGYwxU8O_aB9rsqs8KIYw-1; Fri, 15 May 2020 09:31:41 -0400 X-MC-Unique: bmGYwxU8O_aB9rsqs8KIYw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8474E460; Fri, 15 May 2020 13:31:38 +0000 (UTC) Received: from x1.home (ovpn-112-50.phx2.redhat.com [10.3.112.50]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7D9095C254; Fri, 15 May 2020 13:31:36 +0000 (UTC) Date: Fri, 15 May 2020 07:31:35 -0600 From: Alex Williamson To: Kirti Wankhede Subject: Re: [PATCH Kernel v20 6/8] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap Message-ID: <20200515073135.2370a17d@x1.home> In-Reply-To: <268ec129-a1cb-530a-c9b2-7ec53ddf4d17@nvidia.com> References: <1589488667-9683-1-git-send-email-kwankhede@nvidia.com> <1589488667-9683-7-git-send-email-kwankhede@nvidia.com> <20200514212706.036a336a@x1.home> <5256f488-2d11-eb0f-6980-eea23f4d3019@nvidia.com> <20200514234726.03c2e345@x1.home> <268ec129-a1cb-530a-c9b2-7ec53ddf4d17@nvidia.com> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Received-SPF: pass client-ip=207.211.31.81; envelope-from=alex.williamson@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/15 00:39:12 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Zhengxiao.zx@Alibaba-inc.com, kevin.tian@intel.com, yi.l.liu@intel.com, cjia@nvidia.com, kvm@vger.kernel.org, eskultet@redhat.com, ziye.yang@intel.com, qemu-devel@nongnu.org, cohuck@redhat.com, shuangtai.tst@alibaba-inc.com, dgilbert@redhat.com, zhi.a.wang@intel.com, mlevitsk@redhat.com, pasic@linux.ibm.com, aik@ozlabs.ru, eauger@redhat.com, felipe@nutanix.com, jonathan.davies@nutanix.com, yan.y.zhao@intel.com, changpeng.liu@intel.com, Ken.Xue@amd.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, 15 May 2020 12:17:03 +0530 Kirti Wankhede wrote: > On 5/15/2020 11:17 AM, Alex Williamson wrote: > > On Fri, 15 May 2020 09:46:43 +0530 > > Kirti Wankhede wrote: > > > >> On 5/15/2020 8:57 AM, Alex Williamson wrote: > >>> On Fri, 15 May 2020 02:07:45 +0530 > >>> Kirti Wankhede wrote: > >>> > >>>> DMA mapped pages, including those pinned by mdev vendor drivers, might > >>>> get unpinned and unmapped while migration is active and device is still > >>>> running. For example, in pre-copy phase while guest driver could access > >>>> those pages, host device or vendor driver can dirty these mapped pages. > >>>> Such pages should be marked dirty so as to maintain memory consistency > >>>> for a user making use of dirty page tracking. > >>>> > >>>> To get bitmap during unmap, user should allocate memory for bitmap, set > >>>> it all zeros, set size of allocated memory, set page size to be > >>>> considered for bitmap and set flag VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP. > >>>> > >>>> Signed-off-by: Kirti Wankhede > >>>> Reviewed-by: Neo Jia > >>>> --- > >>>> drivers/vfio/vfio_iommu_type1.c | 77 ++++++++++++++++++++++++++++++++++------- > >>>> include/uapi/linux/vfio.h | 10 ++++++ > >>>> 2 files changed, 75 insertions(+), 12 deletions(-) > >>>> > >>>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > >>>> index b76d3b14abfd..a1dc57bcece5 100644 > >>>> --- a/drivers/vfio/vfio_iommu_type1.c > >>>> +++ b/drivers/vfio/vfio_iommu_type1.c > >>>> @@ -195,11 +195,15 @@ static void vfio_unlink_dma(struct vfio_iommu *iommu, struct vfio_dma *old) > >>>> static int vfio_dma_bitmap_alloc(struct vfio_dma *dma, size_t pgsize) > >>>> { > >>>> uint64_t npages = dma->size / pgsize; > >>>> + size_t bitmap_size; > >>>> > >>>> if (npages > DIRTY_BITMAP_PAGES_MAX) > >>>> return -EINVAL; > >>>> > >>>> - dma->bitmap = kvzalloc(DIRTY_BITMAP_BYTES(npages), GFP_KERNEL); > >>>> + /* Allocate extra 64 bits which are used for bitmap manipulation */ > >>>> + bitmap_size = DIRTY_BITMAP_BYTES(npages) + sizeof(u64); > >>>> + > >>>> + dma->bitmap = kvzalloc(bitmap_size, GFP_KERNEL); > >>>> if (!dma->bitmap) > >>>> return -ENOMEM; > >>>> > >>>> @@ -999,23 +1003,25 @@ static int verify_bitmap_size(uint64_t npages, uint64_t bitmap_size) > >>>> } > >>>> > >>>> static int vfio_dma_do_unmap(struct vfio_iommu *iommu, > >>>> - struct vfio_iommu_type1_dma_unmap *unmap) > >>>> + struct vfio_iommu_type1_dma_unmap *unmap, > >>>> + struct vfio_bitmap *bitmap) > >>>> { > >>>> - uint64_t mask; > >>>> struct vfio_dma *dma, *dma_last = NULL; > >>>> - size_t unmapped = 0; > >>>> + size_t unmapped = 0, pgsize; > >>>> int ret = 0, retries = 0; > >>>> + unsigned long pgshift; > >>>> > >>>> mutex_lock(&iommu->lock); > >>>> > >>>> - mask = ((uint64_t)1 << __ffs(iommu->pgsize_bitmap)) - 1; > >>>> + pgshift = __ffs(iommu->pgsize_bitmap); > >>>> + pgsize = (size_t)1 << pgshift; > >>>> > >>>> - if (unmap->iova & mask) { > >>>> + if (unmap->iova & (pgsize - 1)) { > >>>> ret = -EINVAL; > >>>> goto unlock; > >>>> } > >>>> > >>>> - if (!unmap->size || unmap->size & mask) { > >>>> + if (!unmap->size || unmap->size & (pgsize - 1)) { > >>>> ret = -EINVAL; > >>>> goto unlock; > >>>> } > >>>> @@ -1026,9 +1032,15 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu, > >>>> goto unlock; > >>>> } > >>>> > >>>> - WARN_ON(mask & PAGE_MASK); > >>>> -again: > >>>> + /* When dirty tracking is enabled, allow only min supported pgsize */ > >>>> + if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) && > >>>> + (!iommu->dirty_page_tracking || (bitmap->pgsize != pgsize))) { > >>>> + ret = -EINVAL; > >>>> + goto unlock; > >>>> + } > >>>> > >>>> + WARN_ON((pgsize - 1) & PAGE_MASK); > >>>> +again: > >>>> /* > >>>> * vfio-iommu-type1 (v1) - User mappings were coalesced together to > >>>> * avoid tracking individual mappings. This means that the granularity > >>>> @@ -1066,6 +1078,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu, > >>>> ret = -EINVAL; > >>>> goto unlock; > >>>> } > >>>> + > >>>> dma = vfio_find_dma(iommu, unmap->iova + unmap->size - 1, 0); > >>>> if (dma && dma->iova + dma->size != unmap->iova + unmap->size) { > >>>> ret = -EINVAL; > >>>> @@ -1083,6 +1096,23 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu, > >>>> if (dma->task->mm != current->mm) > >>>> break; > >>>> > >>>> + if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) && > >>>> + (dma_last != dma)) { > >>>> + > >>>> + /* > >>>> + * mark all pages dirty if all pages are pinned and > >>>> + * mapped > >>>> + */ > >>>> + if (dma->iommu_mapped) > >>>> + bitmap_set(dma->bitmap, 0, > >>>> + dma->size >> pgshift); > >>> > >>> Nit, all the callers of update_user_bitmap() precede the call with this > >>> identical operation, we should probably push it into the function to do > >>> it. > >>> > >>>> + > >>>> + ret = update_user_bitmap(bitmap->data, dma, > >>>> + unmap->iova, pgsize); > >>>> + if (ret) > >>>> + break; > >>>> + } > >>>> + > >>> > >>> As noted last time, the above is just busy work if pfn_list is not > >>> already empty. The entire code block above should be moved to after > >>> the block below. Thanks, > >>> > >> > >> pfn_list will be empty for IOMMU backed devices where all pages are > >> pinned and mapped, > > > > Unless we're making use of the selective dirtying introduced in patch > > 8/8 or the container is shared with non-IOMMU backed mdevs. > > > >> but those should be reported as dirty. > > > > I'm confused how that justifies or requires this ordering. > > > > 1. non IOMMU mdev device: > - vendor driver pins pages > - pfn_list is not empty > - device dma or write to pinned pages > > 2. IOMMU backed mdev device or vfio device, but smart driver which pins > required pages > - vendor driver pins pages > - pfn_list is not empty > - device dma or write to pinned pages > > 3. IOMMU backed mdev device or vfio device, driver is not smart > - pages are pinned and mapped during attach > - pfn_list is empty > - device dma or write to any of pinned pages > > For case 3, here this function does bitmap_set(dma->bitmap), that is > mark all pages dirty and then accordingly copy bitmap to user buffer. > Copying dma->bitmap logic remains same. What dependency does case 3 have on pfn_list? Why does it matter if that bitmap_set() occurs before or after we've drained pfn_list? How do we know we're in case 3 before we've looked at pfn_list? > >> So moved it > >> back above empty pfn_list check. > > > > Sorry, it still doesn't make any sense to me, and with no discussion I > > can't differentiate ignored comments from discarded comments. > > > > Pages in the pfn_list contribute to the dirty bitmap when they're > > pinned, we don't depend on pfn_list when reporting the dirty bitmap > > except for re-populating pfn_list dirtied pages after the bitmap has > > been cleared. We're unmapping the dma, so that's not the case here. > > Also since update_user_bitmap() shifts the bitmap in place now, any > > repetitive calls will give us incorrect results. > > Right, but this is unmapping and freeing vfio_dma > > > Therefore, as I see > > it, we _can_ take the branch below and when we do any work we've done > > above is not only wasted but may lead to incorrect data copied to > > the user if we shift dma->bitmap in place more than once. Please > > explain in more detail if you believe this is still correct. Thanks, > > > > In this case also bitmap copy to user happens once, (dma_last != dma) > takes care of making sure that its called only once. I did miss the dma_last check, so that prevents us from repeating this path, BUT we release iommu->lock if we enter the pfn_list !empty path. The moment we do that, we might unblock a vendor driver trying to pin or rw more pages. So the bitmap we've copied to the user might be stale and incorrect. I don't see why this is so contentious, what is the actual disadvantage to moving this until after we've drained pfn_list? The risks seem abundant to me. Thanks, Alex > >>> > >>>> if (!RB_EMPTY_ROOT(&dma->pfn_list)) { > >>>> struct vfio_iommu_type1_dma_unmap nb_unmap; > >>>> > >>>> @@ -2447,17 +2477,40 @@ static long vfio_iommu_type1_ioctl(void *iommu_data, > >>>> > >>>> } else if (cmd == VFIO_IOMMU_UNMAP_DMA) { > >>>> struct vfio_iommu_type1_dma_unmap unmap; > >>>> - long ret; > >>>> + struct vfio_bitmap bitmap = { 0 }; > >>>> + int ret; > >>>> > >>>> minsz = offsetofend(struct vfio_iommu_type1_dma_unmap, size); > >>>> > >>>> if (copy_from_user(&unmap, (void __user *)arg, minsz)) > >>>> return -EFAULT; > >>>> > >>>> - if (unmap.argsz < minsz || unmap.flags) > >>>> + if (unmap.argsz < minsz || > >>>> + unmap.flags & ~VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) > >>>> return -EINVAL; > >>>> > >>>> - ret = vfio_dma_do_unmap(iommu, &unmap); > >>>> + if (unmap.flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) { > >>>> + unsigned long pgshift; > >>>> + > >>>> + if (unmap.argsz < (minsz + sizeof(bitmap))) > >>>> + return -EINVAL; > >>>> + > >>>> + if (copy_from_user(&bitmap, > >>>> + (void __user *)(arg + minsz), > >>>> + sizeof(bitmap))) > >>>> + return -EFAULT; > >>>> + > >>>> + if (!access_ok((void __user *)bitmap.data, bitmap.size)) > >>>> + return -EINVAL; > >>>> + > >>>> + pgshift = __ffs(bitmap.pgsize); > >>>> + ret = verify_bitmap_size(unmap.size >> pgshift, > >>>> + bitmap.size); > >>>> + if (ret) > >>>> + return ret; > >>>> + } > >>>> + > >>>> + ret = vfio_dma_do_unmap(iommu, &unmap, &bitmap); > >>>> if (ret) > >>>> return ret; > >>>> > >>>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h > >>>> index 123de3bc2dce..0a0c7315ddd6 100644 > >>>> --- a/include/uapi/linux/vfio.h > >>>> +++ b/include/uapi/linux/vfio.h > >>>> @@ -1048,12 +1048,22 @@ struct vfio_bitmap { > >>>> * field. No guarantee is made to the user that arbitrary unmaps of iova > >>>> * or size different from those used in the original mapping call will > >>>> * succeed. > >>>> + * VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP should be set to get dirty bitmap > >>>> + * before unmapping IO virtual addresses. When this flag is set, user must > >>>> + * provide data[] as structure vfio_bitmap. User must allocate memory to get > >>>> + * bitmap, zero the bitmap memory and must set size of allocated memory in > >>>> + * vfio_bitmap.size field. A bit in bitmap represents one page of user provided > >>>> + * page size in 'pgsize', consecutively starting from iova offset. Bit set > >>>> + * indicates page at that offset from iova is dirty. Bitmap of pages in the > >>>> + * range of unmapped size is returned in vfio_bitmap.data > >>>> */ > >>>> struct vfio_iommu_type1_dma_unmap { > >>>> __u32 argsz; > >>>> __u32 flags; > >>>> +#define VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP (1 << 0) > >>>> __u64 iova; /* IO virtual address */ > >>>> __u64 size; /* Size of mapping (bytes) */ > >>>> + __u8 data[]; > >>>> }; > >>>> > >>>> #define VFIO_IOMMU_UNMAP_DMA _IO(VFIO_TYPE, VFIO_BASE + 14) > >>> > >> > > >