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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=99c49L3+Zl3kTX1nRDP8/rKylEgF5wqgIgkpMRASmII=; b=VOUwuz3H+YaJu5gQWJqF7bMszELoslcgalzOcKYdfOpJJ0t107Rm8RWz6QZkMsoTS7 FYuV8s/YIKofGB37MxEyXl1YXRGQ39bjcTK260qbZRqEjjph8B1MayN/Zpkgos0GpoeX wGF74+xX08HF6ObOEM9A5IKgDGxNSrPqX72RB7v3+2tGXF9jRNdLDBghQ4pc6qUZDHu0 C2BGOkmZvMerRatFmIZ9ph7iL+Jdnwa/5OE8ivcknuzfzi1oirFnnsoZblWFKrjlEMOy tDMFHlyJQWsLGVIrVuuJBnBUovSMbn0SOfUgotGcFYAv+Un38rPJrpNeDyy1wKpeoPqE lSoQ== X-Gm-Message-State: AOAM5329rcgAP3falxFaHQtxh0wkKxZwiEh+7m8R76r1YGAXI3ECMXai muYhuokIiNZ0EMNjXEtCNh3Pw8rOhy8= X-Google-Smtp-Source: ABdhPJyZ/XhRiHsl9K9UxY9ljR0tWMoMUszGG7V7+fEQHJUTUHMgWx388Q0SI6yFWBEjHdAGcb/X/ywvpiY= X-Received: from oupton.c.googlers.com ([fda3:e722:ac3:cc00:2b:ff92:c0a8:404]) (user=oupton job=sendgmr) by 2002:a25:dc50:: with SMTP id y77mr3336332ybe.484.1627517421452; Wed, 28 Jul 2021 17:10:21 -0700 (PDT) Date: Thu, 29 Jul 2021 00:09:59 +0000 Message-Id: <20210729001012.70394-1-oupton@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.32.0.432.gabb21c7263-goog Subject: [PATCH v4 00/13] KVM: Add idempotent controls for migrating system counter state From: Oliver Upton To: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu Cc: Paolo Bonzini , Sean Christopherson , Marc Zyngier , Peter Shier , Jim Mattson , David Matlack , Ricardo Koller , Jing Zhang , Raghavendra Rao Anata , James Morse , Alexandru Elisei , Suzuki K Poulose , linux-arm-kernel@lists.infradead.org, Andrew Jones , Oliver Upton X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210728_171023_601011_B33206B2 X-CRM114-Status: GOOD ( 22.42 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org KVM's current means of saving/restoring system counters is plagued with temporal issues. At least on ARM64 and x86, we migrate the guest's system counter by-value through the respective guest system register values (cntvct_el0, ia32_tsc). Restoring system counters by-value is brittle as the state is not idempotent: the host system counter is still oscillating between the attempted save and restore. Furthermore, VMMs may wish to transparently live migrate guest VMs, meaning that they include the elapsed time due to live migration blackout in the guest system counter view. The VMM thread could be preempted for any number of reasons (scheduler, L0 hypervisor under nested) between the time that it calculates the desired guest counter value and when KVM actually sets this counter state. Despite the value-based interface that we present to userspace, KVM actually has idempotent guest controls by way of system counter offsets. We can avoid all of the issues associated with a value-based interface by abstracting these offset controls in new ioctls. This series introduces new vCPU device attributes to provide userspace access to the vCPU's system counter offset. Patch 1 adopts Paolo's suggestion, augmenting the KVM_{GET,SET}_CLOCK ioctls to provide userspace with a (host_tsc, realtime) instant. This is essential for a VMM to perform precise migration of the guest's system counters. Patches 2-3 add support for x86 by shoehorning the new controls into the pre-existing synchronization heuristics. Patches 4-5 implement a test for the new additions to KVM_{GET,SET}_CLOCK. Patch 6 fixes some assertions in the kvm device attribute helpers. Patches 7-8 implement at test for the tsc offset attribute introduced in patch 3. Patch 9 adds a device attribute for the arm64 virtual counter-timer offset. Patch 10 extends the test from patch 8 to cover the arm64 virtual counter-timer offset. Patch 11 adds a device attribute for the arm64 physical counter-timer offset. Currently, this is implemented as a synthetic register, forcing the guest to trap to the host and emulating the offset in the fast exit path. Later down the line we will have hardware with FEAT_ECV, which allows the hypervisor to perform physical counter-timer offsetting in hardware (CNTPOFF_EL2). Patch 12 extends the test from patch 8 to cover the arm64 physical counter-timer offset. Patch 13 introduces a benchmark to measure the overhead of emulation in patch 11. This series was tested on both an Ampere Mt. Jade and Haswell systems. Physical counter benchmark -------------------------- The following data was collected by running 10000 iterations of the benchmark test from Patch 6 on an Ampere Mt. Jade reference server, A 2S machine with 2 80-core Ampere Altra SoCs. Measurements were collected for both VHE and nVHE operation using the `kvm-arm.mode=` command-line parameter. nVHE ---- +--------------------+--------+---------+ | Metric | Native | Trapped | +--------------------+--------+---------+ | Average | 54ns | 148ns | | Standard Deviation | 124ns | 122ns | | 95th Percentile | 258ns | 348ns | +--------------------+--------+---------+ VHE --- +--------------------+--------+---------+ | Metric | Native | Trapped | +--------------------+--------+---------+ | Average | 53ns | 152ns | | Standard Deviation | 92ns | 94ns | | 95th Percentile | 204ns | 307ns | +--------------------+--------+---------+ This series applies cleanly to kvm/queue at the following commit: 8ad5e63649ff ("KVM: Don't take mmu_lock for range invalidation unless necessary") v1 -> v2: - Reimplemented as vCPU device attributes instead of a distinct ioctl. - Added the (realtime, host_tsc) instant support to KVM_{GET,SET}_CLOCK - Changed the arm64 implementation to broadcast counter offset values to all vCPUs in a guest. This upholds the architectural expectations of a consistent counter-timer across CPUs. - Fixed a bug with traps in VHE mode. We now configure traps on every transition into a guest to handle differing VMs (trapped, emulated). v2 -> v3: - Added documentation for additions to KVM_{GET,SET}_CLOCK - Added documentation for all new vCPU attributes - Added documentation for suggested algorithm to migrate a guest's TSC(s) - Bug fixes throughout series - Rename KVM_CLOCK_REAL_TIME -> KVM_CLOCK_REALTIME v3 -> v4: - Added patch to address incorrect device helper assertions (Drew) - Carried Drew's r-b tags where appropriate - x86 selftest cleanup - Removed stale kvm_timer_init_vhe() function - Removed unnecessary GUEST_DONE() from selftests v1: https://lore.kernel.org/kvm/20210608214742.1897483-1-oupton@google.com/ v2: https://lore.kernel.org/r/20210716212629.2232756-1-oupton@google.com v3: https://lore/kernel.org/r/20210719184949.1385910-1-oupton@google.com Oliver Upton (13): KVM: x86: Report host tsc and realtime values in KVM_GET_CLOCK KVM: x86: Refactor tsc synchronization code KVM: x86: Expose TSC offset controls to userspace tools: arch: x86: pull in pvclock headers selftests: KVM: Add test for KVM_{GET,SET}_CLOCK selftests: KVM: Fix kvm device helper ioctl assertions selftests: KVM: Add helpers for vCPU device attributes selftests: KVM: Introduce system counter offset test KVM: arm64: Allow userspace to configure a vCPU's virtual offset selftests: KVM: Add support for aarch64 to system_counter_offset_test KVM: arm64: Provide userspace access to the physical counter offset selftests: KVM: Test physical counter offsetting selftests: KVM: Add counter emulation benchmark Documentation/virt/kvm/api.rst | 42 +- Documentation/virt/kvm/devices/vcpu.rst | 101 +++++ Documentation/virt/kvm/locking.rst | 11 + arch/arm64/include/asm/kvm_host.h | 1 + arch/arm64/include/asm/kvm_hyp.h | 2 - arch/arm64/include/asm/sysreg.h | 1 + arch/arm64/include/uapi/asm/kvm.h | 2 + arch/arm64/kvm/arch_timer.c | 140 ++++-- arch/arm64/kvm/arm.c | 4 +- arch/arm64/kvm/hyp/include/hyp/switch.h | 23 + arch/arm64/kvm/hyp/include/hyp/timer-sr.h | 26 ++ arch/arm64/kvm/hyp/nvhe/switch.c | 2 - arch/arm64/kvm/hyp/nvhe/timer-sr.c | 21 +- arch/arm64/kvm/hyp/vhe/timer-sr.c | 27 ++ arch/x86/include/asm/kvm_host.h | 4 + arch/x86/include/uapi/asm/kvm.h | 4 + arch/x86/kvm/x86.c | 422 ++++++++++++++---- include/kvm/arm_arch_timer.h | 2 - include/uapi/linux/kvm.h | 7 +- tools/arch/x86/include/asm/pvclock-abi.h | 48 ++ tools/arch/x86/include/asm/pvclock.h | 103 +++++ tools/testing/selftests/kvm/.gitignore | 3 + tools/testing/selftests/kvm/Makefile | 4 + .../kvm/aarch64/counter_emulation_benchmark.c | 215 +++++++++ .../selftests/kvm/include/aarch64/processor.h | 24 + .../testing/selftests/kvm/include/kvm_util.h | 11 + tools/testing/selftests/kvm/lib/kvm_util.c | 44 +- .../kvm/system_counter_offset_test.c | 206 +++++++++ .../selftests/kvm/x86_64/kvm_clock_test.c | 206 +++++++++ 29 files changed, 1548 insertions(+), 158 deletions(-) create mode 100644 arch/arm64/kvm/hyp/include/hyp/timer-sr.h create mode 100644 tools/arch/x86/include/asm/pvclock-abi.h create mode 100644 tools/arch/x86/include/asm/pvclock.h create mode 100644 tools/testing/selftests/kvm/aarch64/counter_emulation_benchmark.c create mode 100644 tools/testing/selftests/kvm/system_counter_offset_test.c create mode 100644 tools/testing/selftests/kvm/x86_64/kvm_clock_test.c