From: Yu Zhang <[email protected]> Sent: Monday, July 13, 2026 8:34 PM > > On Mon, Jul 13, 2026 at 05:37:51PM +0000, Michael Kelley wrote: > > From: Yu Zhang <[email protected]> Sent: Monday, July 13, 2026 > > 9:46 AM > > > > > > On Sat, Jul 11, 2026 at 06:31:15PM +0000, Michael Kelley wrote: > > > > From: Yu Zhang <[email protected]> Sent: Friday, July 10, > > > > 2026 12:34 AM > > > > [snip] > > > > > > > > > > One new thought: Have you considered the hibernate/resume > > > > cycle? Does anything need to be done with the pvIOMMU to > > > > make it functional again after resume? I see that the Intel and > > > > AMD IOMMU drivers have suspend and resume functions. I > > > > don't know enough about the Hyper-V pvIOMMU to know if it > > > > might also need suspend and resume functions. > > > > > > > > > > Thanks for raising this, Michael. We have not considered such support. > > > > > > My understanding is that the Intel and AMD drivers only disable the > > > IOMMU translation, flush the IOTLB during the suspend and re-enable/ > > > reload the preserved root tables and other HW state during in the > > > resueme. > > > > > > But for pvIOMMU, I guess such job shall be done by the hypervisor? > > > For a device resumed on the same VM, its logical device ID should > > > also remain unchanged? And the corresponding Hyper-V domain objects, > > > configuration, and device attachments shall be preserved and restored > > > by hypervisor? I don't think the current Hyper-V ABI explicitly defines > > > this. But maybe if we want such feature, it could be done by the > > > hypervisor transparently? > > > > > > > I agree with your and Jacob's comments that the guest doesn't have > > any responsibility for saving/restoring IOMMU hardware state, as the > > Intel and AMD IOMMU drivers do. > > > > But yes, I'm wondering about the Hyper-V domain objects and device > > attachments. I doubt Hyper-V can do anything to save and restore > > them. Hibernation is a Linux concept that the Hyper-V host doesn't > > know anything about. > > > > Hibernation is already complicated, and in a VM it is even worse. :-( > > As a start, see Documentation/virt/hyperv/hibernation.rst, which I > > wrote about 18 months ago. It provides some basics as well as outlines > > the additional complexity in a Hyper-V guest VM. I'll also try to spend > > some time thinking through the implications for a pvIOMMU, and let > > you know if I have any more thoughts. > > > > Thank you, Michael, and thanks for pointing us to the documentation. I > need some time to better understand the Linux guest hibernation and resume > flow and its implications for pvIOMMU. > > Meanwhile, do you think this limitation should be documented in the > commit message or the cover letter? >
Yes, I'd say that the lack of hibernation/resume support should be noted in a commit message, probably with Patch 3 of the series. Michael
