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Message-ID: <bab8603f-852a-4581-a6cd-d8958b6f3120@arm.com> Date: Fri, 26 Sep 2025 10:10:36 +0100 From: Steven Price <steven.price@....com> To: "Emi Kisanuki (Fujitsu)" <fj0570is@...itsu.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "kvmarm@...ts.linux.dev" <kvmarm@...ts.linux.dev> Cc: Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>, James Morse <james.morse@....com>, Oliver Upton <oliver.upton@...ux.dev>, Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu <yuzenghui@...wei.com>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Joey Gouly <joey.gouly@....com>, Alexandru Elisei <alexandru.elisei@....com>, Christoffer Dall <christoffer.dall@....com>, Fuad Tabba <tabba@...gle.com>, "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>, Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>, Gavin Shan <gshan@...hat.com>, Shanker Donthineni <sdonthineni@...dia.com>, Alper Gun <alpergun@...gle.com>, "Aneesh Kumar K . V" <aneesh.kumar@...nel.org>, Vishal Annapurve <vannapurve@...gle.com> Subject: Re: [PATCH v10 00/43] arm64: Support for Arm CCA in KVM Hi Emi, Many thanks for testing this! Regards, Steve On 24/09/2025 03:34, Emi Kisanuki (Fujitsu) wrote: > We tested this patch in our internal simulator which is a hardware simulator for Fujitsu's next generation CPU known as Monaka, and it produced the expected results. > > I have verified the following > 1. Launching the realm VM using Internal simulator -> Successfully launched by disabling MPAM support in the ID register. > 2. Running kvm-unit-tests (with lkvm) -> All tests passed except for PMU (as expected, since PMU is not supported by the Internal simulator).[1] > > Tested-by: Emi Kisanuki <fj0570is@...itsu.com> [1] https://gitlab.arm.com/linux-arm/kvmEmi -unit-tests-cca cca/latest > >> This series adds support for running protected VMs using KVM under the Arm >> Confidential Compute Architecture (CCA). >> >> The related guest support was merged for v6.14-rc1 so you no longer need that >> separately. >> >> There are a few changes since v9, many thanks for the review comments. The >> highlights are below, and individual patches have a changelog. >> >> * Fix a potential issue where the host was walking the stage 2 page tables on >> realm destruction. If the RMM didn't zero when undelegated (which it isn't >> required to) then the kernel would attempt to work the junk values and crash. >> >> * Avoid RCU stall warnings by correctly settign may_block in >> kvm_free_stage2_pgd(). >> >> * Rebased onto v6.17-rc1. >> >> Things to note: >> >> * The magic numbers for capabilities and ioctls have been updated. So >> you'll need to update your VMM. See below for the updated kvmtool branch. >> >> * This series doesn't attempt to integrate with the guest-memfd changes that >> are being discussed (see below). >> >> * Vishal raised an important question about what to do in the case of >> undelegate failures (also see below). >> >> guest-memfd >> =========== >> >> This series still implements the same API as previous versions, which means only >> the private memory of the guest is backed by guest-memfd, and the shared >> portion is accessed using VMAs from the VMM. This approach is compatible with >> the proposed changes to support guest-memfd backing shared memory but would >> require the VMM to mmap() the shared memory at the appropriate time so that >> KVM can access via the VMM's VMAs. >> >> Changing to access both shared and private through the guest-memfd API >> shouldn't be difficult and could be done in a backwards compatible manner (with >> the VMM choosing which method to use). It's not clear to me whether we want to >> hold things up waiting for the full guest-memfd (and only support that >> uAPI) or if it would be fine to just support both approaches and let VMM's switch >> when they are ready. >> >> There is a slight wrinkle around the 'populate' uAPI >> (KVM_CAP_ARM_RME_POPULATE). At the moment this expects 'double >> mapping' - the contents to be populated should be in the shared memory region, >> but the physical pages for the private region are also allocated from the >> guest_memfd. >> Arm CCA doesn't support a true 'in-place' conversion so this is required in some >> form. However it may make sense to allow the populate call to take a user space >> pointer for the data to be copied rather than require it to be in the shared memory >> region. We do already have a "flags" argument so there's also scope for easily >> supporting both options. The current approach integrates quite nicely in kvmtool >> with the existing logic for setting up a normal >> (non-CoCo) guest. But I'm aware kvmtool isn't entirely representative of what >> VMMs do, so I'd welcome feedback on what a good populate uAPI would look like. >> >> Undelegation failure >> ==================== >> >> When the kernel is tearing down a CCA VM, it will attempt to "undelegate" >> pages allowing them to be used by the Normal World again. Assuming no bugs >> then these operations will always succeed. However, the RMM has the ability to >> return a failure if it considers these pages to still be in use. A failure like this is >> always a bug in the code, but it would be good to be able to handle these without >> resorting to an immediate BUG_ON(). >> >> The current approach in the code is to simply WARN() and use get_page() to take >> an extra reference to the page to stop it being reused (as it will immediately cause >> a GPF if the Normal World attempts to access the page). >> >> However this will cause problems when we start supporting huge pages. It may be >> possible to use the HWPOISON infrastructure to flag the page as unusable >> (although note there is no way of 'scrubbing' a page to recover from this situation). >> The other option is to just accept this this "should never happen" >> and upgrade the WARN() to a BUG_ON() so we don't have to deal with the >> situation. A third option is to do nothing (other than WARN) and let the system run >> until the inevitable GPF which will probably bring it down (and hope there's >> enough time for the user to save work etc). >> >> I'd welcome thoughts on the best solution. >> >> ==================== >> >> The ABI to the RMM (the RMI) is based on RMM v1.0-rel0 specification[1]. >> >> This series is based on v6.17-rc1. It is also available as a git >> repository: >> >> https://gitlab.arm.com/linux-arm/linux-cca cca-host/v10 >> >> Work in progress changes for kvmtool are available from the git repository below: >> >> https://gitlab.arm.com/linux-arm/kvmtool-cca cca/v8 >> >> [1] https://developer.arm.com/documentation/den0137/1-0rel0/ >> >> Jean-Philippe Brucker (7): >> arm64: RME: Propagate number of breakpoints and watchpoints to >> userspace >> arm64: RME: Set breakpoint parameters through SET_ONE_REG >> arm64: RME: Initialize PMCR.N with number counter supported by RMM >> arm64: RME: Propagate max SVE vector length from RMM >> arm64: RME: Configure max SVE vector length for a Realm >> arm64: RME: Provide register list for unfinalized RME RECs >> arm64: RME: Provide accurate register list >> >> Joey Gouly (2): >> arm64: RME: allow userspace to inject aborts >> arm64: RME: support RSI_HOST_CALL >> >> Steven Price (31): >> arm64: RME: Handle Granule Protection Faults (GPFs) >> arm64: RME: Add SMC definitions for calling the RMM >> arm64: RME: Add wrappers for RMI calls >> arm64: RME: Check for RME support at KVM init >> arm64: RME: Define the user ABI >> arm64: RME: ioctls to create and configure realms >> KVM: arm64: Allow passing machine type in KVM creation >> arm64: RME: RTT tear down >> arm64: RME: Allocate/free RECs to match vCPUs >> KVM: arm64: vgic: Provide helper for number of list registers >> arm64: RME: Support for the VGIC in realms >> KVM: arm64: Support timers in realm RECs >> arm64: RME: Allow VMM to set RIPAS >> arm64: RME: Handle realm enter/exit >> arm64: RME: Handle RMI_EXIT_RIPAS_CHANGE >> KVM: arm64: Handle realm MMIO emulation >> arm64: RME: Allow populating initial contents >> arm64: RME: Runtime faulting of memory >> KVM: arm64: Handle realm VCPU load >> KVM: arm64: Validate register access for a Realm VM >> KVM: arm64: Handle Realm PSCI requests >> KVM: arm64: WARN on injected undef exceptions >> arm64: Don't expose stolen time for realm guests >> arm64: RME: Always use 4k pages for realms >> arm64: RME: Prevent Device mappings for Realms >> arm_pmu: Provide a mechanism for disabling the physical IRQ >> arm64: RME: Enable PMU support with a realm guest >> arm64: RME: Hide KVM_CAP_READONLY_MEM for realm guests >> KVM: arm64: Expose support for private memory >> KVM: arm64: Expose KVM_ARM_VCPU_REC to user space >> KVM: arm64: Allow activating realms >> >> Suzuki K Poulose (3): >> kvm: arm64: Include kvm_emulate.h in kvm/arm_psci.h >> kvm: arm64: Don't expose debug capabilities for realm guests >> arm64: RME: Allow checking SVE on VM instance >> >> Documentation/virt/kvm/api.rst | 92 +- >> arch/arm64/include/asm/kvm_emulate.h | 38 + >> arch/arm64/include/asm/kvm_host.h | 13 +- >> arch/arm64/include/asm/kvm_rme.h | 135 ++ >> arch/arm64/include/asm/rmi_cmds.h | 508 ++++++++ >> arch/arm64/include/asm/rmi_smc.h | 269 ++++ >> arch/arm64/include/asm/virt.h | 1 + >> arch/arm64/include/uapi/asm/kvm.h | 49 + >> arch/arm64/kvm/Kconfig | 1 + >> arch/arm64/kvm/Makefile | 2 +- >> arch/arm64/kvm/arch_timer.c | 44 +- >> arch/arm64/kvm/arm.c | 169 ++- >> arch/arm64/kvm/guest.c | 108 +- >> arch/arm64/kvm/hypercalls.c | 4 +- >> arch/arm64/kvm/inject_fault.c | 5 +- >> arch/arm64/kvm/mmio.c | 16 +- >> arch/arm64/kvm/mmu.c | 209 ++- >> arch/arm64/kvm/pmu-emul.c | 6 + >> arch/arm64/kvm/psci.c | 30 + >> arch/arm64/kvm/reset.c | 23 +- >> arch/arm64/kvm/rme-exit.c | 207 +++ >> arch/arm64/kvm/rme.c | 1746 >> ++++++++++++++++++++++++++ >> arch/arm64/kvm/sys_regs.c | 53 +- >> arch/arm64/kvm/vgic/vgic-init.c | 2 +- >> arch/arm64/kvm/vgic/vgic.c | 61 +- >> arch/arm64/mm/fault.c | 31 +- >> drivers/perf/arm_pmu.c | 15 + >> include/kvm/arm_arch_timer.h | 2 + >> include/kvm/arm_pmu.h | 4 + >> include/kvm/arm_psci.h | 2 + >> include/linux/perf/arm_pmu.h | 5 + >> include/uapi/linux/kvm.h | 29 +- >> 32 files changed, 3778 insertions(+), 101 deletions(-) create mode 100644 >> arch/arm64/include/asm/kvm_rme.h create mode 100644 >> arch/arm64/include/asm/rmi_cmds.h create mode 100644 >> arch/arm64/include/asm/rmi_smc.h create mode 100644 >> arch/arm64/kvm/rme-exit.c create mode 100644 arch/arm64/kvm/rme.c >> >> -- >> 2.43.0 >
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