On Tue, Sep 1, 2020 at 1:15 PM Alexander Graf <graf@xxxxxxxxxx> wrote: > > While tying to add support for the MSR_CORE_THREAD_COUNT MSR in KVM, > I realized that we were still in a world where user space has no control > over what happens with MSR emulation in KVM. > > That is bad for multiple reasons. In my case, I wanted to emulate the > MSR in user space, because it's a CPU specific register that does not > exist on older CPUs and that really only contains informational data that > is on the package level, so it's a natural fit for user space to provide > it. > > However, it is also bad on a platform compatibility level. Currrently, > KVM has no way to expose different MSRs based on the selected target CPU > type. > > This patch set introduces a way for user space to indicate to KVM which > MSRs should be handled in kernel space. With that, we can solve part of > the platform compatibility story. Or at least we can not handle AMD specific > MSRs on an Intel platform and vice versa. > > In addition, it introduces a way for user space to get into the loop > when an MSR access would generate a #GP fault, such as when KVM finds an > MSR that is not handled by the in-kernel MSR emulation or when the guest > is trying to access reserved registers. > > In combination with filtering, user space trapping allows us to emulate > arbitrary MSRs in user space, paving the way for target CPU specific MSR > implementations from user space. > > v1 -> v2: > > - s/ETRAP_TO_USER_SPACE/ENOENT/g > - deflect all #GP injection events to user space, not just unknown MSRs. > That was we can also deflect allowlist errors later > - fix emulator case > - new patch: KVM: x86: Introduce allow list for MSR emulation > - new patch: KVM: selftests: Add test for user space MSR handling > > v2 -> v3: > > - return r if r == X86EMUL_IO_NEEDED > - s/KVM_EXIT_RDMSR/KVM_EXIT_X86_RDMSR/g > - s/KVM_EXIT_WRMSR/KVM_EXIT_X86_WRMSR/g > - Use complete_userspace_io logic instead of reply field > - Simplify trapping code > - document flags for KVM_X86_ADD_MSR_ALLOWLIST > - generalize exit path, always unlock when returning > - s/KVM_CAP_ADD_MSR_ALLOWLIST/KVM_CAP_X86_MSR_ALLOWLIST/g > - Add KVM_X86_CLEAR_MSR_ALLOWLIST > - Add test to clear whitelist > - Adjust to reply-less API > - Fix asserts > - Actually trap on MSR_IA32_POWER_CTL writes > > v3 -> v4: > > - Mention exit reasons in re-enter mandatory section of API documentation > - Clear padding bytes > - Generalize get/set deflect functions > - Remove redundant pending_user_msr field > - lock allow check and clearing > - free bitmaps on clear > > v4 -> v5: > > - use srcu > > v5 -> v6: > > - Switch from allow list to filtering API with explicit fallback option > - Support and test passthrough MSR filtering > - Check for filter exit reason > - Add .gitignore > - send filter change notification > - change to atomic set_msr_filter ioctl with fallback flag > - use EPERM for filter blocks > - add bit for MSR user space deflection > - check for overflow of BITS_TO_LONGS (thanks Dan Carpenter!) > - s/int i;/u32 i;/ > - remove overlap check > - Introduce exit reason mask to allow for future expansion and filtering > - s/emul_to_vcpu(ctxt)/vcpu/ > - imported patch: KVM: x86: Prepare MSR bitmaps for userspace tracked MSRs > - new patch: KVM: x86: Add infrastructure for MSR filtering > - new patch: KVM: x86: SVM: Prevent MSR passthrough when MSR access is denied > - new patch: KVM: x86: VMX: Prevent MSR passthrough when MSR access is denied > > Aaron Lewis (1): > KVM: x86: Prepare MSR bitmaps for userspace tracked MSRs > > Alexander Graf (6): > KVM: x86: Deflect unknown MSR accesses to user space > KVM: x86: Add infrastructure for MSR filtering > KVM: x86: SVM: Prevent MSR passthrough when MSR access is denied > KVM: x86: VMX: Prevent MSR passthrough when MSR access is denied > KVM: x86: Introduce MSR filtering > KVM: selftests: Add test for user space MSR handling > > Documentation/virt/kvm/api.rst | 176 +++++++++- > arch/x86/include/asm/kvm_host.h | 18 ++ > arch/x86/include/uapi/asm/kvm.h | 19 ++ > arch/x86/kvm/emulate.c | 18 +- > arch/x86/kvm/svm/svm.c | 122 +++++-- > arch/x86/kvm/svm/svm.h | 7 + > arch/x86/kvm/vmx/nested.c | 2 +- > arch/x86/kvm/vmx/vmx.c | 303 ++++++++++++------ > arch/x86/kvm/vmx/vmx.h | 9 +- > arch/x86/kvm/x86.c | 267 ++++++++++++++- > arch/x86/kvm/x86.h | 1 + > include/trace/events/kvm.h | 2 +- > include/uapi/linux/kvm.h | 17 + > tools/testing/selftests/kvm/.gitignore | 1 + > tools/testing/selftests/kvm/Makefile | 1 + > .../selftests/kvm/x86_64/user_msr_test.c | 224 +++++++++++++ > 16 files changed, 1055 insertions(+), 132 deletions(-) > create mode 100644 tools/testing/selftests/kvm/x86_64/user_msr_test.c > > -- > 2.17.1 > > > > > Amazon Development Center Germany GmbH > Krausenstr. 38 > 10117 Berlin > Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss > Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B > Sitz: Berlin > Ust-ID: DE 289 237 879 > > > Hi Alex, I'm only seeing 4 commits. Are you planning on sending the remaining 3? Thanks, Aaron
