This patch series adds support for PCI pass-thru devices to Hyper-V Confidential VMs (also called "Isolation VMs"). But in preparation, it first changes how private (encrypted) vs. shared (decrypted) memory is handled in Hyper-V SEV-SNP guest VMs. The new approach builds on the confidential computing (coco) mechanisms introduced in the 5.19 kernel for TDX support and significantly reduces the amount of Hyper-V specific code. Furthermore, with this new approach a proposed RFC patch set for generic DMA layer functionality[1] is no longer necessary. Background ========== Hyper-V guests on AMD SEV-SNP hardware have the option of using the "virtual Top Of Memory" (vTOM) feature specified by the SEV-SNP architecture. With vTOM, shared vs. private memory accesses are controlled by splitting the guest physical address space into two halves. vTOM is the dividing line where the uppermost bit of the physical address space is set; e.g., with 47 bits of guest physical address space, vTOM is 0x40000000000 (bit 46 is set). Guest phyiscal memory is accessible at two parallel physical addresses -- one below vTOM and one above vTOM. Accesses below vTOM are private (encrypted) while accesses above vTOM are shared (decrypted). In this sense, vTOM is like the GPA.SHARED bit in Intel TDX. In Hyper-V's use of vTOM, the normal guest OS runs at VMPL2, while a Hyper-V provided "paravisor" runs at VMPL0 in the guest VM. (VMPL is Virtual Machine Privilege Level. See AMD's SEV-SNP spec for more details.) The paravisor provides emulation for various system devices like the I/O APIC as part of the guest VM. Accesses to such devices made by the normal guest OS trap to the paravisor and are emulated in the guest VM context instead of in the Hyper-V host. This emulation is invisible to the normal guest OS, but with the quirk that memory mapped I/O accesses to these devices must be treated as private, not shared as would be the case for other device accesses. Support for Hyper-V guests using vTOM was added to the Linux kernel in two patch sets[2][3]. This support treats the vTOM bit as part of the physical address. For accessing shared (decrypted) memory, the core approach is to create a second kernel virtual mapping that maps to parallel physical addresses above vTOM, while leaving the original mapping unchanged. Most of the code for creating that second virtual mapping is confined to Hyper-V specific areas, but there are are also changes to generic swiotlb code. Changes in this patch set ========================= In preparation for supporting PCI pass-thru devices, this patch set changes the core approach for handling vTOM. In the new approach, the vTOM bit is treated as a protection flag, and not as part of the physical address. This new approach is like the approach for the GPA.SHARED bit in Intel TDX. Furthermore, there's no need to create a second kernel virtual mapping. When memory is changed between private and shared using set_memory_decrypted() and set_memory_encrypted(), the PTEs for the existing kernel mapping are changed to add or remove the vTOM bit just as with TDX. The hypercalls to change the memory status on the host side are made using the existing callback mechanism. Everything just works, with a minor tweak to map the I/O APIC to use private accesses as mentioned above. With the new handling of vTOM in place, existing Hyper-V code that creates the second kernel virtual mapping still works, but it is now redundant as the original kernel virtual mapping (as updated) maps to the same physical address. To simplify things going forward, this patch set removes the code that creates the second kernel virtual mapping. And since a second kernel virtual mapping is no longer needed, the changes to the DMA layer proposed as an RFC[1] are no longer needed. Finally, to support PCI pass-thru in a Confidential VM, Hyper-V requires that all accesses to PCI config space be emulated using a hypercall. This patch set adds functions to invoke those hypercalls and uses them in the config space access functions in the Hyper-V PCI driver. Lastly, the Hyper-V PCI driver is marked as allowed to be used in a Confidential VM. The Hyper-V PCI driver has been hardened against a malicious Hyper-V in a previous patch set.[4] Patch Organization ================== Patch 1 fixes a bug in __ioremap_caller() that affects the existing Hyper-V code after the change to treat the vTOM bit as a protection flag. Fixing the bug allows the old code to continue to run until later patches in the series remove or update it. This sequencing avoids the need to enable the new approach and remove the old code in a single large patch. Patch 2 handles the I/O APIC quirk by defining a new CC_ATTR enum member that is set only when running on Hyper-V. Patch 3 does some simple reordering of code to facilitate Patch 5. Patch 4 tweaks calls to vmap_pfn() in the old Hyper-V code that are deleted in later patches in the series. Like Patch 1, this patch helps avoid the need to enable the new approach and remove the old code in a single large patch. Patch 5 enables the new approach to handling vTOM for Hyper-V guest VMs. Patches 6 thru 9 remove existing code for creating a second kernel virtual mapping. Patch 10 updates existing code so that it no longer assumes that the vTOM bit is part of the physical address. Patch 11 adds the new hypercalls for accessing MMIO Config Space. Patch 12 updates the PCI Hyper-V driver to use the new hypercalls and enables the PCI Hyper-V driver to be used in a Confidential VM. [1] https://lore.kernel.org/lkml/20220706195027.76026-1-parri.andrea@xxxxxxxxx/ [2] https://lore.kernel.org/all/20211025122116.264793-1-ltykernel@xxxxxxxxx/ [3] https://lore.kernel.org/all/20211213071407.314309-1-ltykernel@xxxxxxxxx/ [4] https://lore.kernel.org/all/20220511223207.3386-1-parri.andrea@xxxxxxxxx/ Michael Kelley (12): x86/ioremap: Fix page aligned size calculation in __ioremap_caller() x86/ioapic: Gate decrypted mapping on cc_platform_has() attribute x86/hyperv: Reorder code in prep for subsequent patch Drivers: hv: Explicitly request decrypted in vmap_pfn() calls x86/hyperv: Change vTOM handling to use standard coco mechanisms swiotlb: Remove bounce buffer remapping for Hyper-V Drivers: hv: vmbus: Remove second mapping of VMBus monitor pages Drivers: hv: vmbus: Remove second way of mapping ring buffers hv_netvsc: Remove second mapping of send and recv buffers Drivers: hv: Don't remap addresses that are above shared_gpa_boundary PCI: hv: Add hypercalls to read/write MMIO space PCI: hv: Enable PCI pass-thru devices in Confidential VMs arch/x86/coco/core.c | 10 +- arch/x86/hyperv/hv_init.c | 7 +- arch/x86/hyperv/ivm.c | 121 ++++++++++---------- arch/x86/include/asm/hyperv-tlfs.h | 3 + arch/x86/include/asm/mshyperv.h | 8 +- arch/x86/kernel/apic/io_apic.c | 3 +- arch/x86/kernel/cpu/mshyperv.c | 22 ++-- arch/x86/mm/ioremap.c | 2 +- arch/x86/mm/pat/set_memory.c | 6 +- drivers/hv/Kconfig | 1 - drivers/hv/channel_mgmt.c | 2 +- drivers/hv/connection.c | 113 +++++-------------- drivers/hv/hv.c | 23 ++-- drivers/hv/hv_common.c | 11 -- drivers/hv/hyperv_vmbus.h | 2 - drivers/hv/ring_buffer.c | 62 ++++------- drivers/net/hyperv/hyperv_net.h | 2 - drivers/net/hyperv/netvsc.c | 48 +------- drivers/pci/controller/pci-hyperv.c | 215 +++++++++++++++++++++++++----------- include/asm-generic/hyperv-tlfs.h | 22 ++++ include/asm-generic/mshyperv.h | 2 - include/linux/cc_platform.h | 13 +++ include/linux/swiotlb.h | 2 - kernel/dma/swiotlb.c | 45 +------- 24 files changed, 343 insertions(+), 402 deletions(-) -- 1.8.3.1
