Messages in this thread | | | Date | Wed, 16 Nov 2022 10:41:34 +0800 | Subject | Re: [PATCH v10 077/108] KVM: x86: Add a switch_db_regs flag to handle TDX's auto-switched behavior | From | Binbin Wu <> |
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On 10/30/2022 2:23 PM, isaku.yamahata@intel.com wrote: > From: Isaku Yamahata <isaku.yamahata@intel.com> > > Add a flag, KVM_DEBUGREG_AUTO_SWITCHED_GUEST, to skip saving/restoring DRs > irrespective of any other flags. TDX-SEAM unconditionally saves and > restores guest DRs and reset to architectural INIT state on TD exit. > So, KVM needs to save host DRs before TD enter without restoring guest DRs > and restore host DRs after TD exit. > > Opportunistically convert the KVM_DEBUGREG_* definitions to use BIT(). > > Reported-by: Xiaoyao Li <xiaoyao.li@intel.com> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> > Co-developed-by: Chao Gao <chao.gao@intel.com> > Signed-off-by: Chao Gao <chao.gao@intel.com> > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com> > --- > arch/x86/include/asm/kvm_host.h | 9 +++++++-- > arch/x86/kvm/vmx/tdx.c | 1 + > arch/x86/kvm/x86.c | 11 ++++++++--- > 3 files changed, 16 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index fdb00d96e954..082e94f78c66 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -583,8 +583,13 @@ struct kvm_pmu { > struct kvm_pmu_ops; > > enum { > - KVM_DEBUGREG_BP_ENABLED = 1, > - KVM_DEBUGREG_WONT_EXIT = 2, > + KVM_DEBUGREG_BP_ENABLED = BIT(0), > + KVM_DEBUGREG_WONT_EXIT = BIT(1), > + /* > + * Guest debug registers are saved/restored by hardware on exit from > + * or enter guest. KVM needn't switch them. > + */ > + KVM_DEBUGREG_AUTO_SWITCH = BIT(2), > }; > > struct kvm_mtrr_range { > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c > index fc4de83a2df8..57767ef3353b 100644 > --- a/arch/x86/kvm/vmx/tdx.c > +++ b/arch/x86/kvm/vmx/tdx.c > @@ -429,6 +429,7 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu) > > vcpu->arch.efer = EFER_SCE | EFER_LME | EFER_LMA | EFER_NX; > > + vcpu->arch.switch_db_regs = KVM_DEBUGREG_AUTO_SWITCH; > vcpu->arch.cr0_guest_owned_bits = -1ul; > vcpu->arch.cr4_guest_owned_bits = -1ul; > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 4d4b71c4cdb1..ad7b227b68dd 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -10779,7 +10779,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > if (vcpu->arch.guest_fpu.xfd_err) > wrmsrl(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err); > > - if (unlikely(vcpu->arch.switch_db_regs)) { > + if (unlikely(vcpu->arch.switch_db_regs & ~KVM_DEBUGREG_AUTO_SWITCH)) { > set_debugreg(0, 7); > set_debugreg(vcpu->arch.eff_db[0], 0); > set_debugreg(vcpu->arch.eff_db[1], 1); > @@ -10822,6 +10822,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > */ > if (unlikely(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT)) { > WARN_ON(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP); > + WARN_ON(vcpu->arch.switch_db_regs & KVM_DEBUGREG_AUTO_SWITCH); > static_call(kvm_x86_sync_dirty_debug_regs)(vcpu); > kvm_update_dr0123(vcpu); > kvm_update_dr7(vcpu); > @@ -10834,8 +10835,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > * care about the messed up debug address registers. But if > * we have some of them active, restore the old state. > */ > - if (hw_breakpoint_active()) > - hw_breakpoint_restore(); > + if (hw_breakpoint_active()) { > + if (!(vcpu->arch.switch_db_regs & KVM_DEBUGREG_AUTO_SWITCH)) > + hw_breakpoint_restore(); > + else > + set_debugreg(__this_cpu_read(cpu_dr7), 7);
Why only restore dr7 when TD exit?
According to the commit message, dr0~dr3 are also reset to architectural INIT value on TD exit.
> + } > > vcpu->arch.last_vmentry_cpu = vcpu->cpu; > vcpu->arch.last_guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc());
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