Messages in this thread | | | Subject | Re: [RESEND PATCH 1/2] KVM: X86: Add support for the emulation of DR6_BUS_LOCK bit | From | Chenyi Qiang <> | Date | Wed, 27 Jan 2021 09:48:38 +0800 |
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On 1/27/2021 12:31 AM, Paolo Bonzini wrote: > On 08/01/21 07:49, Chenyi Qiang wrote: >> To avoid breaking the CPUs without bus lock detection, activate the >> DR6_BUS_LOCK bit (bit 11) conditionally in DR6_FIXED_1 bits. >> >> The set/clear of DR6_BUS_LOCK is similar to the DR6_RTM in DR6 >> register. The processor clears DR6_BUS_LOCK when bus lock debug >> exception is generated. (For all other #DB the processor sets this bit >> to 1.) Software #DB handler should set this bit before returning to the >> interrupted task. >> >> For VM exit caused by debug exception, bit 11 of the exit qualification >> is set to indicate that a bus lock debug exception condition was >> detected. The VMM should emulate the exception by clearing bit 11 of the >> guest DR6. > > Please rename DR6_INIT to DR6_ACTIVE_LOW, and then a lot of changes > become simpler: > >> - dr6 |= DR6_BD | DR6_RTM; >> + dr6 |= DR6_BD | DR6_RTM | DR6_BUS_LOCK; > > dr6 |= DR6_BD | DR6_ACTIVE_LOW; > >> ctxt->ops->set_dr(ctxt, 6, dr6); >> return emulate_db(ctxt); >> } >> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c >> index cce0143a6f80..3d8a0e30314f 100644 >> --- a/arch/x86/kvm/svm/svm.c >> +++ b/arch/x86/kvm/svm/svm.c >> @@ -1860,7 +1860,7 @@ static void svm_sync_dirty_debug_regs(struct >> kvm_vcpu *vcpu) >> get_debugreg(vcpu->arch.db[2], 2); >> get_debugreg(vcpu->arch.db[3], 3); >> /* >> - * We cannot reset svm->vmcb->save.dr6 to DR6_FIXED_1|DR6_RTM here, >> + * We cannot reset svm->vmcb->save.dr6 to >> DR6_FIXED_1|DR6_RTM|DR6_BUS_LOCK here, > > We cannot reset svm->vmcb->save.dr6 to DR6_ACTIVE_LOW > >> * because db_interception might need it. We can do it before >> vmentry. >> */ >> vcpu->arch.dr6 = svm->vmcb->save.dr6; >> @@ -1911,7 +1911,7 @@ static int db_interception(struct vcpu_svm *svm) >> if (!(svm->vcpu.guest_debug & >> (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP)) && >> !svm->nmi_singlestep) { >> - u32 payload = (svm->vmcb->save.dr6 ^ DR6_RTM) & ~DR6_FIXED_1; >> + u32 payload = (svm->vmcb->save.dr6 ^ (DR6_RTM|DR6_BUS_LOCK)) >> & ~DR6_FIXED_1; > > u32 payload = svm->vmcb->save.dr6 ^ DR6_ACTIVE_LOW; > >> kvm_queue_exception_p(&svm->vcpu, DB_VECTOR, payload); >> return 1; >> } >> @@ -3778,7 +3778,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct >> kvm_vcpu *vcpu) >> if (unlikely(svm->vcpu.arch.switch_db_regs & >> KVM_DEBUGREG_WONT_EXIT)) >> svm_set_dr6(svm, vcpu->arch.dr6); >> else >> - svm_set_dr6(svm, DR6_FIXED_1 | DR6_RTM); >> + svm_set_dr6(svm, DR6_FIXED_1 | DR6_RTM | DR6_BUS_LOCK); > > svm_set_dr6(svm, DR6_ACTIVE_LOW); > >> clgi(); >> kvm_load_guest_xsave_state(vcpu); >> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c >> index e2f26564a12d..c5d71a9b3729 100644 >> --- a/arch/x86/kvm/vmx/nested.c >> +++ b/arch/x86/kvm/vmx/nested.c >> @@ -412,7 +412,7 @@ static int nested_vmx_check_exception(struct >> kvm_vcpu *vcpu, unsigned long *exit >> if (!has_payload) { >> payload = vcpu->arch.dr6; >> payload &= ~(DR6_FIXED_1 | DR6_BT); >> - payload ^= DR6_RTM; >> + payload ^= DR6_RTM | DR6_BUS_LOCK; > > payload &= ~DR6_BT; > payload ^= DR6_ACTIVE_LOW; > >> } >> *exit_qual = payload; >> } else >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 3f7c1fc7a3ce..06de2b9e57f3 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -483,19 +483,20 @@ void kvm_deliver_exception_payload(struct >> kvm_vcpu *vcpu) >> */ >> vcpu->arch.dr6 &= ~DR_TRAP_BITS; >> /* >> - * DR6.RTM is set by all #DB exceptions that don't clear it. >> + * DR6.RTM and DR6.BUS_LOCK are set by all #DB exceptions >> + * that don't clear it. >> */ >> - vcpu->arch.dr6 |= DR6_RTM; >> + vcpu->arch.dr6 |= DR6_RTM | DR6_BUS_LOCK; >> vcpu->arch.dr6 |= payload; >> /* >> - * Bit 16 should be set in the payload whenever the #DB >> - * exception should clear DR6.RTM. This makes the payload >> - * compatible with the pending debug exceptions under VMX. >> - * Though not currently documented in the SDM, this also >> - * makes the payload compatible with the exit qualification >> - * for #DB exceptions under VMX. >> + * Bit 16/Bit 11 should be set in the payload whenever >> + * the #DB exception should clear DR6.RTM/DR6.BUS_LOCK. >> + * This makes the payload compatible with the pending debug >> + * exceptions under VMX. Though not currently documented in >> + * the SDM, this also makes the payload compatible with the >> + * exit qualification for #DB exceptions under VMX. >> */ >> - vcpu->arch.dr6 ^= payload & DR6_RTM; >> + vcpu->arch.dr6 ^= payload & (DR6_RTM | DR6_BUS_LOCK); > > vcpu->arch.dr6 &= ~DR_TRAP_BITS; > vcpu->arch.dr6 |= DR6_ACTIVE_LOW; > vcpu->arch.dr6 |= payload; > vcpu->arch.dr6 ^= payload & DR6_ACTIVE_LOW; > > (with comments :)) > > and so on. > > Thanks! > > Paolo >
Will do the changes.
Thanks! Chenyi
>> /* >> * The #DB payload is defined as compatible with the 'pending >> @@ -1126,6 +1127,9 @@ static u64 kvm_dr6_fixed(struct kvm_vcpu *vcpu) >> if (!guest_cpuid_has(vcpu, X86_FEATURE_RTM)) >> fixed |= DR6_RTM; >> + >> + if (!guest_cpuid_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT)) >> + fixed |= DR6_BUS_LOCK; >> return fixed; >> } >> @@ -7197,7 +7201,8 @@ static int kvm_vcpu_do_singlestep(struct >> kvm_vcpu *vcpu) >> struct kvm_run *kvm_run = vcpu->run; >> if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) { >> - kvm_run->debug.arch.dr6 = DR6_BS | DR6_FIXED_1 | DR6_RTM; >> + kvm_run->debug.arch.dr6 = DR6_BS | DR6_FIXED_1 | DR6_RTM | >> + DR6_BUS_LOCK; >> kvm_run->debug.arch.pc = kvm_get_linear_rip(vcpu); >> kvm_run->debug.arch.exception = DB_VECTOR; >> kvm_run->exit_reason = KVM_EXIT_DEBUG; >> @@ -7241,7 +7246,8 @@ static bool kvm_vcpu_check_breakpoint(struct >> kvm_vcpu *vcpu, int *r) >> vcpu->arch.eff_db); >> if (dr6 != 0) { >> - kvm_run->debug.arch.dr6 = dr6 | DR6_FIXED_1 | DR6_RTM; >> + kvm_run->debug.arch.dr6 = dr6 | DR6_FIXED_1 | DR6_RTM | >> + DR6_BUS_LOCK; >> kvm_run->debug.arch.pc = eip; >> kvm_run->debug.arch.exception = DB_VECTOR; >> kvm_run->exit_reason = KVM_EXIT_DEBUG; >> >
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