Given the high cost of NX hugepages in terms of TLB performance, it may be desirable to disable the mitigation on a per-VM basis. In the case of public cloud providers with many VMs on a single host, some VMs may be more trusted than others. In order to maximize performance on critical VMs, while still providing some protection to the host from iTLB Multihit, allow the mitigation to be selectively disabled. Disabling NX hugepages on a VM is relatively straightforward, but I took this as an opportunity to add some NX hugepages test coverage and clean up selftests infrastructure a bit. This series was tested with the new selftest and the rest of the KVM selftests on an Intel Haswell machine. The following tests failed, but I do not believe that has anything to do with this series: userspace_io_test vmx_nested_tsc_scaling_test vmx_preemption_timer_test Changelog: v1->v2: Dropped the complicated memslot refactor in favor of Ricardo Koller's patch with a similar effect. Incorporated David Dunn's feedback and reviewed by tag: shortened waits to speed up test. v2->v3: Incorporated a suggestion from David on how to build the NX huge pages test. Fixed a build breakage identified by David. Dropped the per-vm nx_huge_pages field in favor of simply checking the global + per-VM disable override. Documented the new capability Separated out the commit to test disabling NX huge pages Removed permission check when checking if the disable NX capability is supported. Added test coverage for the permission check. v3->v4: Collected RB's from Jing and David Modified stat collection to reduce a memory allocation [David] Incorporated various improvments to the NX test [David] Changed the NX disable test to run by default [David] Removed some now unnecessary commits Dropped the code to dump KVM stats from the binary stats test, and factor out parts of the existing test to library functions instead. [David, Jing, Sean] Dropped the improvement to a debugging log message as it's no longer relevant to this series. Ben Gardon (10): KVM: selftests: Remove dynamic memory allocation for stats header KVM: selftests: Read binary stats header in lib KVM: selftests: Read binary stats desc in lib KVM: selftests: Read binary stat data in lib KVM: selftests: Add NX huge pages test KVM: x86/MMU: Factor out updating NX hugepages state for a VM KVM: x86/MMU: Allow NX huge pages to be disabled on a per-vm basis KVM: x86: Fix errant brace in KVM capability handling KVM: x86/MMU: Require reboot permission to disable NX hugepages KVM: selftests: Test disabling NX hugepages on a VM Documentation/virt/kvm/api.rst | 13 ++ arch/x86/include/asm/kvm_host.h | 2 + arch/x86/kvm/mmu.h | 10 +- arch/x86/kvm/mmu/mmu.c | 17 +- arch/x86/kvm/mmu/spte.c | 7 +- arch/x86/kvm/mmu/spte.h | 3 +- arch/x86/kvm/mmu/tdp_mmu.c | 3 +- arch/x86/kvm/x86.c | 17 +- include/uapi/linux/kvm.h | 1 + tools/testing/selftests/kvm/Makefile | 10 + .../selftests/kvm/include/kvm_util_base.h | 11 + .../selftests/kvm/kvm_binary_stats_test.c | 75 +++---- tools/testing/selftests/kvm/lib/kvm_util.c | 125 ++++++++++- .../selftests/kvm/x86_64/nx_huge_pages_test.c | 198 ++++++++++++++++++ .../kvm/x86_64/nx_huge_pages_test.sh | 25 +++ 15 files changed, 453 insertions(+), 64 deletions(-) create mode 100644 tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c create mode 100755 tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh -- 2.35.1.1178.g4f1659d476-goog
