| Message ID | 20210424004645.3950558-1-seanjc@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: x86: vCPU RESET/INIT fixes and consolidation | expand |
On 24/04/21 02:46, Sean Christopherson wrote: > For the record, I went into this thinking it was going to be a simple code > shuffle between {svm,vmx}_vcpu_reset() and kvm_vcpu_reset(). The actual > goal is to consolidate the RESET/INIT code, both to deduplicate code and > to try to avoid divergent behavior/bugs, e.g. SVM only recently started > updating vcpu->arch.cr4 on INIT. > > The TL;DR of why it takes 40+ patches to get there is that the RESET/INIT > flows have multiple latent bugs and hidden dependencies, but "work" > because they're rarely touched, are mostly fixed flows in both KVM and the > guest, and because guests don't sanity check state after INIT. > > While several of the patches have Fixes tags, I am absolutely terrified of > backporting most of them due to the likelihood of breaking a different > version of KVM. And, for the most part the bugs are benign in the sense > no guest has actually encountered any of these bugs. For that reason, I > intentionally omitted stable@ entirely. The only patches I would consider > even remotely safe for backporting are the first two patches in the series. > > > Sean Christopherson (43): > KVM: nVMX: Set LDTR to its architecturally defined value on nested > VM-Exit > KVM: VMX: Set EDX at INIT with CPUID.0x1, Family-Model-Stepping > KVM: SVM: Require exact CPUID.0x1 match when stuffing EDX at INIT > KVM: SVM: Fall back to KVM's hardcoded value for EDX at RESET/INIT > KVM: x86: Split out CR0/CR4 MMU role change detectors to separate > helpers > KVM: x86: Properly reset MMU context at vCPU RESET/INIT > KVM: VMX: Remove explicit MMU reset in enter_rmode() > KVM: SVM: Drop explicit MMU reset at RESET/INIT > KVM: SVM: Drop a redundant init_vmcb() from svm_create_vcpu() > KVM: VMX: Move init_vmcs() invocation to vmx_vcpu_reset() > KVM: x86: WARN if the APIC map is dirty without an in-kernel local > APIC > KVM: x86: Remove defunct BSP "update" in local APIC reset > KVM: x86: Migrate the PIT only if vcpu0 is migrated, not any BSP > KVM: x86: Don't force set BSP bit when local APIC is managed by > userspace > KVM: x86: Set BSP bit in reset BSP vCPU's APIC base by default > KVM: VMX: Stuff vcpu->arch.apic_base directly at vCPU RESET > KVM: x86: Open code necessary bits of kvm_lapic_set_base() at vCPU > RESET > KVM: x86: Consolidate APIC base RESET initialization code > KVM: x86: Move EDX initialization at vCPU RESET to common code > KVM: SVM: Don't bother writing vmcb->save.rip at vCPU RESET/INIT > KVM: VMX: Invert handling of CR0.WP for EPT without unrestricted guest > KVM: VMX: Remove direct write to vcpu->arch.cr0 during vCPU RESET/INIT > KVM: VMX: Fold ept_update_paging_mode_cr0() back into vmx_set_cr0() > KVM: nVMX: Do not clear CR3 load/store exiting bits if L1 wants 'em > KVM: VMX: Pull GUEST_CR3 from the VMCS iff CR3 load exiting is > disabled > KVM: VMX: Process CR0.PG side effects after setting CR0 assets > KVM: VMX: Skip emulation required checks during pmode/rmode > transitions > KVM: nVMX: Don't evaluate "emulation required" on VM-Exit > KVM: SVM: Tweak order of cr0/cr4/efer writes at RESET/INIT > KVM: SVM: Drop redundant writes to vmcb->save.cr4 at RESET/INIT > KVM: SVM: Stuff save->dr6 at during VMSA sync, not at RESET/INIT > KVM: VMX: Skip pointless MSR bitmap update when setting EFER > KVM: VMX: Refresh list of user return MSRs after setting guest CPUID > KVM: VMX: Don't _explicitly_ reconfigure user return MSRs on vCPU INIT > KVM: x86: Move setting of sregs during vCPU RESET/INIT to common x86 > KVM: VMX: Remove obsolete MSR bitmap refresh at vCPU RESET/INIT > KVM: nVMX: Remove obsolete MSR bitmap refresh at nested transitions > KVM: VMX: Don't redo x2APIC MSR bitmaps when userspace filter is > changed > KVM: VMX: Remove unnecessary initialization of msr_bitmap_mode > KVM: VMX: Smush x2APIC MSR bitmap adjustments into single function > KVM: VMX: Remove redundant write to set vCPU as active at RESET/INIT > KVM: VMX: Drop VMWRITEs to zero fields at vCPU RESET > KVM: x86: Drop pointless @reset_roots from kvm_init_mmu() > > arch/x86/include/asm/kvm_host.h | 5 - > arch/x86/kvm/i8254.c | 3 +- > arch/x86/kvm/lapic.c | 26 +-- > arch/x86/kvm/mmu.h | 2 +- > arch/x86/kvm/mmu/mmu.c | 13 +- > arch/x86/kvm/svm/nested.c | 2 +- > arch/x86/kvm/svm/sev.c | 1 + > arch/x86/kvm/svm/svm.c | 33 +--- > arch/x86/kvm/vmx/nested.c | 26 ++- > arch/x86/kvm/vmx/vmx.c | 271 +++++++++++++------------------- > arch/x86/kvm/vmx/vmx.h | 5 +- > arch/x86/kvm/x86.c | 51 +++++- > 12 files changed, 189 insertions(+), 249 deletions(-) > I'm waiting for a v2 of this; it applies with relatively few conflicts, but there were some comments so it's better if you take care of updating it. Paolo
On Thu, Jun 10, 2021, Paolo Bonzini wrote: > I'm waiting for a v2 of this; it applies with relatively few conflicts, but > there were some comments so it's better if you take care of updating it. Ya, slowly getting there... Something in this series (I can't even remember what) sent me into the morass that is unsync shadow pages and I've been thrashing around in there for a while.
For the record, I went into this thinking it was going to be a simple code shuffle between {svm,vmx}_vcpu_reset() and kvm_vcpu_reset(). The actual goal is to consolidate the RESET/INIT code, both to deduplicate code and to try to avoid divergent behavior/bugs, e.g. SVM only recently started updating vcpu->arch.cr4 on INIT. The TL;DR of why it takes 40+ patches to get there is that the RESET/INIT flows have multiple latent bugs and hidden dependencies, but "work" because they're rarely touched, are mostly fixed flows in both KVM and the guest, and because guests don't sanity check state after INIT. While several of the patches have Fixes tags, I am absolutely terrified of backporting most of them due to the likelihood of breaking a different version of KVM. And, for the most part the bugs are benign in the sense no guest has actually encountered any of these bugs. For that reason, I intentionally omitted stable@ entirely. The only patches I would consider even remotely safe for backporting are the first two patches in the series. Sean Christopherson (43): KVM: nVMX: Set LDTR to its architecturally defined value on nested VM-Exit KVM: VMX: Set EDX at INIT with CPUID.0x1, Family-Model-Stepping KVM: SVM: Require exact CPUID.0x1 match when stuffing EDX at INIT KVM: SVM: Fall back to KVM's hardcoded value for EDX at RESET/INIT KVM: x86: Split out CR0/CR4 MMU role change detectors to separate helpers KVM: x86: Properly reset MMU context at vCPU RESET/INIT KVM: VMX: Remove explicit MMU reset in enter_rmode() KVM: SVM: Drop explicit MMU reset at RESET/INIT KVM: SVM: Drop a redundant init_vmcb() from svm_create_vcpu() KVM: VMX: Move init_vmcs() invocation to vmx_vcpu_reset() KVM: x86: WARN if the APIC map is dirty without an in-kernel local APIC KVM: x86: Remove defunct BSP "update" in local APIC reset KVM: x86: Migrate the PIT only if vcpu0 is migrated, not any BSP KVM: x86: Don't force set BSP bit when local APIC is managed by userspace KVM: x86: Set BSP bit in reset BSP vCPU's APIC base by default KVM: VMX: Stuff vcpu->arch.apic_base directly at vCPU RESET KVM: x86: Open code necessary bits of kvm_lapic_set_base() at vCPU RESET KVM: x86: Consolidate APIC base RESET initialization code KVM: x86: Move EDX initialization at vCPU RESET to common code KVM: SVM: Don't bother writing vmcb->save.rip at vCPU RESET/INIT KVM: VMX: Invert handling of CR0.WP for EPT without unrestricted guest KVM: VMX: Remove direct write to vcpu->arch.cr0 during vCPU RESET/INIT KVM: VMX: Fold ept_update_paging_mode_cr0() back into vmx_set_cr0() KVM: nVMX: Do not clear CR3 load/store exiting bits if L1 wants 'em KVM: VMX: Pull GUEST_CR3 from the VMCS iff CR3 load exiting is disabled KVM: VMX: Process CR0.PG side effects after setting CR0 assets KVM: VMX: Skip emulation required checks during pmode/rmode transitions KVM: nVMX: Don't evaluate "emulation required" on VM-Exit KVM: SVM: Tweak order of cr0/cr4/efer writes at RESET/INIT KVM: SVM: Drop redundant writes to vmcb->save.cr4 at RESET/INIT KVM: SVM: Stuff save->dr6 at during VMSA sync, not at RESET/INIT KVM: VMX: Skip pointless MSR bitmap update when setting EFER KVM: VMX: Refresh list of user return MSRs after setting guest CPUID KVM: VMX: Don't _explicitly_ reconfigure user return MSRs on vCPU INIT KVM: x86: Move setting of sregs during vCPU RESET/INIT to common x86 KVM: VMX: Remove obsolete MSR bitmap refresh at vCPU RESET/INIT KVM: nVMX: Remove obsolete MSR bitmap refresh at nested transitions KVM: VMX: Don't redo x2APIC MSR bitmaps when userspace filter is changed KVM: VMX: Remove unnecessary initialization of msr_bitmap_mode KVM: VMX: Smush x2APIC MSR bitmap adjustments into single function KVM: VMX: Remove redundant write to set vCPU as active at RESET/INIT KVM: VMX: Drop VMWRITEs to zero fields at vCPU RESET KVM: x86: Drop pointless @reset_roots from kvm_init_mmu() arch/x86/include/asm/kvm_host.h | 5 - arch/x86/kvm/i8254.c | 3 +- arch/x86/kvm/lapic.c | 26 +-- arch/x86/kvm/mmu.h | 2 +- arch/x86/kvm/mmu/mmu.c | 13 +- arch/x86/kvm/svm/nested.c | 2 +- arch/x86/kvm/svm/sev.c | 1 + arch/x86/kvm/svm/svm.c | 33 +--- arch/x86/kvm/vmx/nested.c | 26 ++- arch/x86/kvm/vmx/vmx.c | 271 +++++++++++++------------------- arch/x86/kvm/vmx/vmx.h | 5 +- arch/x86/kvm/x86.c | 51 +++++- 12 files changed, 189 insertions(+), 249 deletions(-)