On Fri, May 18, 2018 at 12:04:04AM +0300, Michael S. Tsirkin wrote: > On Thu, May 17, 2018 at 04:59:15PM +0800, Peter Xu wrote: > > (Hello, Jintack, Feel free to test this branch again against your scp > > error case when you got free time) > > > > I rewrote some of the patches in V3. Major changes: > > > > - Dropped mergable interval tree, instead introduced IOVA tree, which > > is even simpler. > > > > - Fix the scp error issue that Jintack reported. Please see patches > > for detailed information. That's the major reason to rewrite a few > > of the patches. We use replay for domain flushes are possibly > > incorrect in the past. The thing is that IOMMU replay has an > > "definition" that "we should only send MAP when new page detected", > > while for shadow page syncing we actually need something else than > > that. So in this version I started to use a new > > vtd_sync_shadow_page_table() helper to do the page sync. > > > > - Some other refines after the refactoring. > > > > I'll add unit test for the IOVA tree after this series merged to make > > sure we won't switch to another new tree implementaion... > > > > The element size in the new IOVA tree should be around > > sizeof(GTreeNode + IOMMUTLBEntry) ~= (5*8+4*8) = 72 bytes. So the > > worst case usage ratio would be 72/4K=2%, which still seems acceptable > > (it means 8G L2 guest will use 8G*2%=160MB as metadata to maintain the > > mapping in QEMU). > > > > I did explicit test with scp this time, copying 1G sized file for >10 > > times on each of the following case: > > > > - L1 guest, with vIOMMU and with assigned device > > - L2 guest, without vIOMMU and with assigned device > > - L2 guest, with vIOMMU (so 3-layer nested IOMMU) and with assigned device > > > > Please review. Thanks, > > > > (Below are old content from previous cover letter) > > > > ========================== > > > > v2: > > - fix patchew code style warnings > > - interval tree: postpone malloc when inserting; simplify node remove > > a bit where proper [Jason] > > - fix up comment and commit message for iommu lock patch [Kevin] > > - protect context cache too using the iommu lock [Kevin, Jason] > > - add vast comment in patch 8 to explain the modify-PTE problem > > [Jason, Kevin] > > > > Online repo: > > > > https://github.com/xzpeter/qemu/tree/fix-vtd-dma > > > > This series fixes several major problems that current code has: > > > > - Issue 1: when getting very big PSI UNMAP invalidations, the current > > code is buggy in that we might skip the notification while actually > > we should always send that notification. > > security issue > > > - Issue 2: IOTLB is not thread safe, while block dataplane can be > > accessing and updating it in parallel. > > security issue > > > - Issue 3: For devices that only registered with UNMAP-only notifiers, > > we don't really need to do page walking for PSIs, we can directly > > deliver the notification down. For example, vhost. > > optimization > > > - Issue 4: unsafe window for MAP notified devices like vfio-pci (and > > in the future, vDPA as well). The problem is that, now for domain > > invalidations we do this to make sure the shadow page tables are > > correctly synced: > > > > 1. unmap the whole address space > > 2. replay the whole address space, map existing pages > > > > However during step 1 and 2 there will be a very tiny window (it can > > be as big as 3ms) that the shadow page table is either invalid or > > incomplete (since we're rebuilding it up). That's fatal error since > > devices never know that happending and it's still possible to DMA to > > memories. > > correctness but not a security issue > > > Patch 1 fixes issue 1. I put it at the first since it's picked from > > an old post. > > > > Patch 2 is a cleanup to remove useless IntelIOMMUNotifierNode struct. > > > > Patch 3 fixes issue 2. > > > > Patch 4 fixes issue 3. > > > > Patch 5-9 fix issue 4. Here a very simple interval tree is > > implemented based on Gtree. It's different with general interval tree > > in that it does not allow user to pass in private data (e.g., > > translated addresses). However that benefits us that then we can > > merge adjacent interval leaves so that hopefully we won't consume much > > memory even if the mappings are a lot (that happens for nested virt - > > when mapping the whole L2 guest RAM range, it can be at least in GBs). > > > > Patch 10 is another big cleanup only can work after patch 9. > > > So 1-2 are needed on stable. 1-9 would be nice to have > there too, even though they are big and it looks risky.
Yes, although issue 4 is not a security issue, but it might cause DMA errors and unusability of devices to happen. I don't know very much on the details of how stable tree should treat patches like this, but considering that this whole series only touches VT-d code, and as you mentioned merely all the patches would be nice to have even for stable, I'll just CC stable for all the patches, refine messages and repost. Thanks, -- Peter Xu
