> -----Original Message----- > From: Jan Beulich <jbeul...@suse.com> > Sent: 05 September 2019 15:30 > To: Paul Durrant <paul.durr...@citrix.com> > Cc: xen-devel@lists.xenproject.org; Julien Grall <julien.gr...@arm.com>; > Alexandru Isaila > <aisa...@bitdefender.com>; PetrePircalabu <ppircal...@bitdefender.com>; > Razvan Cojocaru > <rcojoc...@bitdefender.com>; Andrew Cooper <andrew.coop...@citrix.com>; Roger > Pau Monne > <roger....@citrix.com>; Volodymyr Babchuk <volodymyr_babc...@epam.com>; > George Dunlap > <george.dun...@citrix.com>; Ian Jackson <ian.jack...@citrix.com>; Stefano > Stabellini > <sstabell...@kernel.org>; Konrad Rzeszutek Wilk <konrad.w...@oracle.com>; > Tamas K Lengyel > <ta...@tklengyel.com>; Tim (Xen.org) <t...@xen.org>; Wei Liu <w...@xen.org> > Subject: Re: [PATCH v8 4/6] remove late (on-demand) construction of IOMMU > page tables > > On 02.09.2019 16:50, Paul Durrant wrote: > > Now that there is a per-domain IOMMU-enable flag, which should be set if > > any device is going to be passed through, stop deferring page table > > construction until the assignment is done. Also don't tear down the tables > > again when the last device is de-assigned; defer that task until domain > > destruction. > > > > This allows the has_iommu_pt() helper and iommu_status enumeration to be > > removed. Calls to has_iommu_pt() are simply replaced by calls to > > is_iommu_enabled(). Remaining open-coded tests of iommu_hap_pt_share can > > also be replaced by calls to iommu_use_hap_pt(). > > The arch_iommu_populate_page_table() and iommu_construct() functions become > > redundant, as does the 'strict mode' dom0 page_list mapping code in > > iommu_hwdom_init(), and iommu_teardown() can be made static is its only > > remaining caller, iommu_domain_destroy(), is within the same source > > module. > > > > All in all, about 220 lines of code are removed from the hypervisor. > > > > NOTE: This patch will cause a small amount of extra resource to be used > > to accommodate IOMMU page tables that may never be used, since the > > per-domain IOMMU-enable flag is currently set to the value of the > > global iommu_enable flag. A subsequent patch will add an option to > > the toolstack to allow it to be turned off if there is no intention > > to assign passthrough hardware to the domain. > > To account for the extra resource, 'iommu_memkb' has been added to > > domain_build_info. This patch sets it unconditionally to a value > > calculated based on the domain's maximum memory but, when the > > toolstack option mentioned above is added, it can be set to zero > > if the per-domain IOMMU-enable flag is turned off. > > > > Signed-off-by: Paul Durrant <paul.durr...@citrix.com> > > I've just stumbled across our earlier discussion on the still not > sufficiently "x86/HVM: p2m_ram_ro is incompatible with device > pass-through" of mine, and I wonder whether the implication from > the change here is that people wanting p2m_ram_ro used on a guest > would then need to force the IOMMU off for that guest (which aiui > isn't possible until patch 6).
You wouldn't be able to force IOMMU off on a per-domain basis until patch #6 but it could still be done globally. Paul > > Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
