| Message ID | 20180828160459.14093-1-sean.j.christopherson@intel.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: nVMX: add option to perform early consistency checks via H/W | expand |
On Tue, Aug 28, 2018 at 09:04:41AM -0700, Sean Christopherson wrote: > KVM currently defers many VMX consistency checks to the CPU, including > checks that result in VMFail (as opposed to VMExit). This behavior > may be undesirable for some users since this means KVM detects certain > classes of VMFail only after it has processed guest state. Because > there is a strict ordering between checks that cause VMFail and those > that cause VMExit, i.e. all VMFail checks are performed before any > checks that cause VMExit, we can detect all VMFail conditions via a > dry run of sorts. > > The end goal of this series is to add an optional (param-controlled) > pre-run VMEnter into the nested_vmx_run() flow in order to perform > all VMFail consistency checks prior to actually running vmcs02. By > itself, this is not a complex process, but getting KVM to a point > where the approach is viable requires a fair amount of refactoring, > e.g. to split prepare_vmcs02() so that there is a point where vmcs02 > can pass the VMFail checks without first consuming guest state. > > And while the goal (and subject) of this series is to enable early > consistency checks, the vast majority of the series deals with bug > fixes and cleanups in the nested VMX code. During the refactoring > and testing, a number of pre-existing bugs, opportunities for code > cleanup and easy optimization points (which unconvered more bugs) > were encountered. > > Ideally, these patches would be split into 3-4 separate series, > especially the bug fix patches. I smushed everything into a single > series because the early VMEnter code breaks without the bug fixes > and the refactoring shuffles the same code, and some of the cleanup > and fixes are inter-dependent. > > Patch Synopsis: > 1-4: bug fixes > 5-6: optimizations > 7: function rename > 8: bug fix and refactoring > 9-12: refactoring > 13-14: bug fix > 15: refactoring > 16: optimization and prereq for early consistency checks > 17-18: early consistency checks Has anyone had a chance to look at any of these patches, especially patches 1-16? I'm fairly indifferent with regard to getting the early consistency check stuff in mainline, but I'd like to get the bug fixes and refactoring upstreamed sooner rather than later. I can attempt to break this into multiple series if bundling everything together is unpalatable. > v1: https://www.spinics.net/lists/kvm/msg172795.html > > v2: > - rebased on tag kvm-4.19-2 > - added patch to skip instr in nested_vmx_{fail,succeed} > > Sean Christopherson (18): > KVM: nVMX: move host EFER consistency checks to VMFail path > KVM: nVMX: move vmcs12 EPTP consistency check to > check_vmentry_prereqs() > KVM: nVMX: use vm_exit_controls_init() to write exit controls for > vmcs02 > KVM: nVMX: reset cache/shadows on nested consistency check VMExit > KVM: vmx: do not unconditionally clear EFER switching > KVM: nVMX: try to set EFER bits correctly when init'ing entry controls > KVM: nVMX: rename enter_vmx_non_root_mode to > nested_vmx_enter_non_root_mode > KVM: nVMX: move check_vmentry_postreqs() call to > nested_vmx_enter_non_root_mode() > KVM: nVMX: assimilate nested_vmx_entry_failure() into > nested_vmx_enter_non_root_mode() > KVM: nVMX: split pieces of prepare_vmcs02() to prepare_vmcs02_early() > KVM: nVMX: do early preparation of vmcs02 before > check_vmentry_postreqs() > KVM: vVMX: rename label for post-enter_guest_mode consistency check > KVM: nVMX: do not skip VMEnter instruction that succeeds > KVM: nVMX: do not call nested_vmx_succeed() for consistency check > VMExit > KVM: nVMX: call kvm_skip_emulated_instruction in > nested_vmx_{fail,succeed} > KVM: vmx: write HOST_IA32_EFER in vmx_set_constant_host_state() > KVM: nVMX: add option to perform early consistency checks via H/W > KVM: nVMX: WARN if nested run hits VMFail with early consistency > checks enabled > > arch/x86/kvm/vmx.c | 972 ++++++++++++++++++++++++++------------------- > 1 file changed, 556 insertions(+), 416 deletions(-) > > -- > 2.18.0 >
On 06/09/2018 17:23, Sean Christopherson wrote: > Has anyone had a chance to look at any of these patches, especially > patches 1-16? I'm fairly indifferent with regard to getting the early > consistency check stuff in mainline, but I'd like to get the bug fixes > and refactoring upstreamed sooner rather than later. I can attempt to > break this into multiple series if bundling everything together is > unpalatable. > Back from vacation, I'll look at this series this week. I find it a very useful tool, and actually I'm thinking of adding a Kconfig symbol to enable early_consistency_checks by default. Distros may want to enable it in their debug kernels. Paolo
On Mon, 2018-09-10 at 13:44 +0200, Paolo Bonzini wrote: > On 06/09/2018 17:23, Sean Christopherson wrote: > > > > Has anyone had a chance to look at any of these patches, especially > > patches 1-16? I'm fairly indifferent with regard to getting the early > > consistency check stuff in mainline, but I'd like to get the bug fixes > > and refactoring upstreamed sooner rather than later. I can attempt to > > break this into multiple series if bundling everything together is > > unpalatable. > > > Back from vacation, I'll look at this series this week. I find it a > very useful tool, and actually I'm thinking of adding a Kconfig symbol > to enable early_consistency_checks by default. Distros may want to > enable it in their debug kernels. Thanks! I need to tweak patch 17/18[1], I'll wait to do that until you've had a chance to review the rest of the series. [1] Using GUEST_RIP to force the consistency check VMExit doesn't work on 32-bit since we can't write bits 63:32 (thankfully 0-Day caught this issue). GUEST_RFLAGS is a good (and maybe better) alternative. I'll also enhance the changelog to explain the reasoning behind using GUEST_RFLAGS.
KVM currently defers many VMX consistency checks to the CPU, including checks that result in VMFail (as opposed to VMExit). This behavior may be undesirable for some users since this means KVM detects certain classes of VMFail only after it has processed guest state. Because there is a strict ordering between checks that cause VMFail and those that cause VMExit, i.e. all VMFail checks are performed before any checks that cause VMExit, we can detect all VMFail conditions via a dry run of sorts. The end goal of this series is to add an optional (param-controlled) pre-run VMEnter into the nested_vmx_run() flow in order to perform all VMFail consistency checks prior to actually running vmcs02. By itself, this is not a complex process, but getting KVM to a point where the approach is viable requires a fair amount of refactoring, e.g. to split prepare_vmcs02() so that there is a point where vmcs02 can pass the VMFail checks without first consuming guest state. And while the goal (and subject) of this series is to enable early consistency checks, the vast majority of the series deals with bug fixes and cleanups in the nested VMX code. During the refactoring and testing, a number of pre-existing bugs, opportunities for code cleanup and easy optimization points (which unconvered more bugs) were encountered. Ideally, these patches would be split into 3-4 separate series, especially the bug fix patches. I smushed everything into a single series because the early VMEnter code breaks without the bug fixes and the refactoring shuffles the same code, and some of the cleanup and fixes are inter-dependent. Patch Synopsis: 1-4: bug fixes 5-6: optimizations 7: function rename 8: bug fix and refactoring 9-12: refactoring 13-14: bug fix 15: refactoring 16: optimization and prereq for early consistency checks 17-18: early consistency checks v1: https://www.spinics.net/lists/kvm/msg172795.html v2: - rebased on tag kvm-4.19-2 - added patch to skip instr in nested_vmx_{fail,succeed} Sean Christopherson (18): KVM: nVMX: move host EFER consistency checks to VMFail path KVM: nVMX: move vmcs12 EPTP consistency check to check_vmentry_prereqs() KVM: nVMX: use vm_exit_controls_init() to write exit controls for vmcs02 KVM: nVMX: reset cache/shadows on nested consistency check VMExit KVM: vmx: do not unconditionally clear EFER switching KVM: nVMX: try to set EFER bits correctly when init'ing entry controls KVM: nVMX: rename enter_vmx_non_root_mode to nested_vmx_enter_non_root_mode KVM: nVMX: move check_vmentry_postreqs() call to nested_vmx_enter_non_root_mode() KVM: nVMX: assimilate nested_vmx_entry_failure() into nested_vmx_enter_non_root_mode() KVM: nVMX: split pieces of prepare_vmcs02() to prepare_vmcs02_early() KVM: nVMX: do early preparation of vmcs02 before check_vmentry_postreqs() KVM: vVMX: rename label for post-enter_guest_mode consistency check KVM: nVMX: do not skip VMEnter instruction that succeeds KVM: nVMX: do not call nested_vmx_succeed() for consistency check VMExit KVM: nVMX: call kvm_skip_emulated_instruction in nested_vmx_{fail,succeed} KVM: vmx: write HOST_IA32_EFER in vmx_set_constant_host_state() KVM: nVMX: add option to perform early consistency checks via H/W KVM: nVMX: WARN if nested run hits VMFail with early consistency checks enabled arch/x86/kvm/vmx.c | 972 ++++++++++++++++++++++++++------------------- 1 file changed, 556 insertions(+), 416 deletions(-)