Event channels, yeah. That really is where I started. It was all so simple in Joao and Ankur's original version at https://www.spinics.net/lists/kvm/msg182556.html — just a handful of simple test_and_set_bit() calls on the mapped page. When I posted v1 I didn't quite understand how steal time and nesting were safely using the kvm_map_gfn() function, and I posted the Xen part declaring that I had "reduced it to a previously solved problem". Then I frowned at kvm_map_gfn() for a bit longer, concluded it was basically impossible to use it safely on its own because the page it maps might belong to another guest by the time it even returns to its caller, and posted a v2 in which I did something safer for myself by hooking into the MMU notifiers. I then fixed the steal time reporting, and killed gfn_to_pfn_cache, under separate cover. In v3 of this series I re-introduce a saner gfn_to_pfn_cache with MMU notifier support to give it proper invalidation semantics. This can now be used for the Xen event channel support and should also be usable for fixing the various use-after-free races in the nesting code too — the last patch in this series being an untested proof of concept attempt at fixing one such. Since adding a C file in virt/kvm/ was somewhat more painful than it really should have been, there is a small detour into all the arch specific Makefiles to make them include a common one. Intended for merging up to patch 11. Patch 12 is for illustration. David Woodhouse (12): KVM: Introduce CONFIG_HAVE_KVM_DIRTY_RING KVM: Add Makefile.kvm for common files, use it for x86 KVM: s390: Use Makefile.kvm for common files KVM: mips: Use Makefile.kvm for common files KVM: RISC-V: Use Makefile.kvm for common files KVM: powerpc: Use Makefile.kvm for common files KVM: arm64: Use Makefile.kvm for common files KVM: Propagate vcpu explicitly to mark_page_dirty_in_slot() KVM: Reinstate gfn_to_pfn_cache with invalidation support KVM: x86/xen: Maintain valid mapping of Xen shared_info page KVM: x86/xen: Add KVM_IRQ_ROUTING_XEN_EVTCHN and event channel delivery KVM: x86: First attempt at converting nested virtual APIC page to gpc Documentation/virt/kvm/api.rst | 21 ++ arch/arm64/kvm/Makefile | 6 +- arch/arm64/kvm/mmu.c | 2 +- arch/mips/kvm/Makefile | 3 +- arch/powerpc/kvm/Makefile | 6 +- arch/riscv/kvm/Makefile | 6 +- arch/s390/kvm/Makefile | 6 +- arch/x86/include/asm/kvm_host.h | 4 +- arch/x86/kvm/Kconfig | 2 + arch/x86/kvm/Makefile | 7 +- arch/x86/kvm/irq_comm.c | 12 + arch/x86/kvm/mmu/mmu.c | 2 +- arch/x86/kvm/mmu/spte.c | 2 +- arch/x86/kvm/mmu/tdp_mmu.c | 2 +- arch/x86/kvm/vmx/nested.c | 50 +++- arch/x86/kvm/vmx/vmx.c | 12 +- arch/x86/kvm/vmx/vmx.h | 2 +- arch/x86/kvm/x86.c | 17 +- arch/x86/kvm/xen.c | 287 +++++++++++++++++++-- arch/x86/kvm/xen.h | 9 + include/linux/kvm_dirty_ring.h | 14 +- include/linux/kvm_host.h | 100 ++++++- include/linux/kvm_types.h | 18 ++ include/uapi/linux/kvm.h | 11 + .../testing/selftests/kvm/x86_64/xen_shinfo_test.c | 112 +++++++- virt/kvm/Kconfig | 6 + virt/kvm/Makefile.kvm | 14 + virt/kvm/dirty_ring.c | 10 +- virt/kvm/kvm_main.c | 34 ++- virt/kvm/{mmu_lock.h => kvm_mm.h} | 23 +- virt/kvm/pfncache.c | 281 ++++++++++++++++++++ 31 files changed, 992 insertions(+), 89 deletions(-)
