On Tue, Apr 18, 2017 at 01:51:19PM +1000, Gavin Shan wrote: >On Thu, Apr 13, 2017 at 07:27:32AM -0500, Bjorn Helgaas wrote: >>On Thu, Apr 13, 2017 at 05:53:55PM +1000, Gavin Shan wrote: >>> On Fri, Mar 31, 2017 at 10:24:06AM +1100, Gavin Shan wrote: >>> >On Tue, Mar 21, 2017 at 09:50:06AM +1100, Gavin Shan wrote: >>> >>On Mon, Mar 20, 2017 at 10:46:44AM -0500, Bjorn Helgaas wrote: >>> >>>On Sat, Mar 18, 2017 at 11:19:07AM +1100, Gavin Shan wrote: >>> >>>> On Thu, Mar 09, 2017 at 11:34:32AM +1100, Gavin Shan wrote: >>> >>>> >On Tue, Mar 07, 2017 at 02:15:29PM -0600, Bjorn Helgaas wrote: >>> >>>> >>On Mon, Feb 27, 2017 at 11:18:32AM +1100, Gavin Shan wrote: >>> >>>> >>> The PowerNV platform is the only user of pcibios_sriov_disable(). >>> >>>> >>> The IOV BAR could be shifted by pci_iov_update_resource(). The >>> >>>> >>> warning message in the function is printed if the IOV capability >>> >>>> >>> is in enabled (PCI_SRIOV_CTRL_VFE && PCI_SRIOV_CTRL_MSE) state. >>> >>>> >>> >>> >>>> >>> pci_disable_sriov >>> >>>> >>> sriov_disable >>> >>>> >>> pnv_pci_sriov_disable >>> >>>> >>> pnv_pci_vf_resource_shift >>> >>>> >>> pci_update_resource >>> >>>> >>> pci_iov_update_resource >>> >>>> >>> >>> >>>> >>> This fixes the issue by disabling IOV capability before calling >>> >>>> >>> pcibios_sriov_disable(). With it, the disabling path matches with >>> >>>> >>> the enabling path: pcibios_sriov_enable() is called before the >>> >>>> >>> IOV capability is enabled. >>> >>>> >> >>> >>>> >>I'm vaguely uncomfortable about this path: >>> >>>> >> >>> >>>> >> pci_disable_sriov >>> >>>> >> sriov_disable >>> >>>> >> pcibios_sriov_disable # powerpc version >>> >>>> >> pnv_pci_sriov_disable >>> >>>> >> pnv_pci_vf_resource_shift >>> >>>> >> res = &dev->resource[i + PCI_IOV_RESOURCES] >>> >>>> >> res->start += size * offset >>> >>>> >> pci_update_resource >>> >>>> >> pci_iov_update_resource >>> >>>> >> pnv_pci_vf_release_m64 >>> >>>> >> >>> >>>> >>1) "res" is already in the resource tree, so we shouldn't be changing >>> >>>> >> its start address, because that may make the tree inconsistent, >>> >>>> >> e.g., the resource may no longer be completely contained in its >>> >>>> >> parent, it may conflict with a sibling, etc. >>> >>>> >> >>> >>>> >>2) If we update "res->start", shouldn't we update "res->end" >>> >>>> >> correspondingly? >>> >>>> >> >>> >>>> >>It seems like it'd be better if we didn't update the device resources >>> >>>> >>in the enable/disable paths. If we could do the resource adjustments >>> >>>> >>earlier, somewhere before we give the device to a driver, it seems >>> >>>> >>like it would avoid these issues. >>> >>>> >> >>> >>>> >>We might have talked about these questions in the past, so I apologize >>> >>>> >>if you've already explained this. If that's the case, maybe we just >>> >>>> >>need some comments in the code to help the next confused reader. >>> >>>> >> >>> >>>> > >>> >>>> >Bjorn, thanks for review. I agree it's not perfect. We discussed this long >>> >>>> >time ago as I can remember. Let me try to make it a bit more clear: In our >>> >>>> >PHB hardware, there are 16 MMIO BARs. Each of them can be shared by 256 PEs >>> >>>> >(A) and owned exclusively by one PE (B). When VF BAR size is small enough, >>> >>>> >we take (A). Otherwise, we have to take (B). Only when taking (A), we need >>> >>>> >expand/move/shrink the IOV BAR. So lets stick to (A) for discussion here. >>> >>>> > >>> >>>> >Under (A), PF's IOV BAR size is extended to ((256 * (VF BAR size)) when the >>> >>>> >PF is probed. Then the @res, which corresponds to the IOV BAR, is assigned >>> >>>> >and put into the resource tree during resource sizing and assignment stage. >>> >>>> >The IOV capability is going to be enabled by PF's driver or sysfs entry, it >>> >>>> >calls into pnv_pci_sriov_enable() where number of contigous PEs (equal to >>> >>>> >number of VFs to be enabled) are allocated. We shift the IOV BAR base according >>> >>>> >to the starting PE number of the allocated block. Afterewards, the IOV BAR >>> >>>> >is restored when the IOV capability is disabled. So it's all about the PE. >>> >>>> >The IOV BAR's end address isn't touched, we needn't update @res->end when >>> >>>> >restoring the IOV BAR. >>> >>>> > >>> >>>> >In order to avoid moving IOV BAR base address, I need know the the PEs >>> >>>> >for the VFs before resourcd sizing and assignment stage. It means I need >>> >>>> >to reserve PEs in advance, which isn't nice because we never enable the >>> >>>> >VFs. In that case, the PEs are wasted. >>> >>>> > >>> >>>> >Yeah, it's nice to have add some comments in pnv_pci_vf_resource_shift() >>> >>>> >where pci_update_resource() is called. I will post another patch to >>> >>>> >linux-ppcdev and you'll be copied. If you agree, I think you can merge >>> >>>> >this patch as none of the concerns are too much related. >>> >>>> > >>> >>>> >>> >>>> Sorry, Bjorn, ping! Please let me know if there are more concerns you have. >>> >>> >>> >>>I think we had a misunderstanding -- you mentioned adding some >>> >>>comments and wrote "I will post another patch", and I *thought* you >>> >>>meant you were going to post another version of *this* patch with some >>> >>>updated comments. So I've been waiting for that updated patch. But I >>> >>>think you've been waiting for me to merge *this* patch as-is. >>> >>> >>> >>>To avoid having this discussion a third time in the future, I think >>> >>>you should add some comments at the point where you update the >>> >>>resource. Updating a resource after it's in the resource tree is >>> >>>clearly dangerous, so we need some explanation of why it's sort of OK >>> >>>in this particular case. >>> >>> >>> >>>If you can write a comment and dig up a URL to our previous >>> >>>discussion, I'd like to incorporate that into *this* patch before I >>> >>>merge it. The sooner we can document this, the less work it will be >>> >>>in the future. >>> >>> >>> >> >>> >>Ok. Sorry for the confusion and that I should looked into the code for more. >>> >>We already had one comment like below in arch/powerpc/platforms/powernv/pci-ioda.c:: >>> >>pnv_pci_vf_resource_shift(). I think it's exactly what you like to have, please >>> >>help to confirm. I believe it was added based on your comments long time ago when >>> >>you review the SRIOV (for PowerNV) patches. >>> >> >>> >> /* >>> >> * After doing so, there would be a "hole" in the /proc/iomem when >>> >> * offset is a positive value. It looks like the device return some >>> >> * mmio back to the system, which actually no one could use it. >>> >> */ >>> >> >>> >>http://www.spinics.net/lists/linux-pci/msg39424.html >>> >> >>> > >>> >Bjorn, please let me know if you have concerns. >>> > >>> >>> Bjorn, Sorry that I have to ping you again. I assume it's mergable. >>> Please let me know if you have more concerns. >> >>I'm not going to merge this without a comment in >>pnv_pci_vf_resource_shift() that addresses the two questions I raised >>in my very first response. I don't think the existing comment about >>"After doing so, there would be a 'hole'" is sufficient. If it were >>sufficient, I wouldn't have raised the questions in the first place. >> >>The resource tree relies on properties like "the sibling list is >>ordered by res->start" and "a child is completely contained within its >>parent". pnv_pci_vf_resource_shift() does this: >> >> res->start += size * offset; >> >>That could easily break both of those properties, so you need to >>provide a way for a reader to verify that it actually does not break >>them. >> >>You can write that comment, or I can do it myself. Either way, it's >>going to take me a while to figure out again what's going on there >>because it is definitely outside the usual resource management model. >> > >Bjorn, thanks for providing more information about the concerns, but I >think original comments are sufficient if I don't miss anything here. > >The expansion and shrinking on the IOV BAR (res->start) don't change the >order of its sibling list because the adjusted "res->start" should be >in the boundary of original IOV BAR. However, it's true there is a "hole" >in IOV BAR's parent and it would be taken by someone else in theory, >but it is rare or even impossible for someone else to request resource >in the "hole" because the "hole" isn't known by anyone except the platform >itself. Besides, the IOV BAR resource shouldn't have children when the >function (pnv_pci_vf_resource_shift()) is called. > >Summary: When we're going to update the IOV BAR, the BAR (resource) isn't >stable and usable. It is the assumption and I don't see anything wrong >about it. > Bjorn, could you guide how to proceed with this? :) Cheers, Gavin
