diff mbox series

[RESEND,1/2] KVM: X86: Add support for the emulation of DR6_BUS_LOCK bit

Message ID 20210108064924.1677-2-chenyi.qiang@intel.com (mailing list archive)
State New, archived
Headers show
Series Add KVM support for bus lock debug exception | expand

Commit Message

Chenyi Qiang Jan. 8, 2021, 6:49 a.m. UTC 
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.

Co-developed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com>
---
 arch/x86/include/asm/kvm_host.h |  5 +++--
 arch/x86/kvm/emulate.c          |  2 +-
 arch/x86/kvm/svm/svm.c          |  6 +++---
 arch/x86/kvm/vmx/nested.c       |  2 +-
 arch/x86/kvm/vmx/vmx.c          |  6 ++++--
 arch/x86/kvm/x86.c              | 28 +++++++++++++++++-----------
 6 files changed, 29 insertions(+), 20 deletions(-)

Comments

kernel test robot Jan. 8, 2021, 4:38 p.m. UTC | #1 
Hi Chenyi,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on kvm/linux-next]
[also build test ERROR on v5.11-rc2 next-20210108]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Chenyi-Qiang/Add-KVM-support-for-bus-lock-debug-exception/20210108-144848
base:   https://git.kernel.org/pub/scm/virt/kvm/kvm.git linux-next
config: i386-randconfig-r015-20210108 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-15) 9.3.0
reproduce (this is a W=1 build):
        # https://github.com/0day-ci/linux/commit/b1bac74da16aca55f4fb7f49c18849a5e3f66ae7
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Chenyi-Qiang/Add-KVM-support-for-bus-lock-debug-exception/20210108-144848
        git checkout b1bac74da16aca55f4fb7f49c18849a5e3f66ae7
        # save the attached .config to linux build tree
        make W=1 ARCH=i386 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   In file included from include/asm-generic/bug.h:5,
                    from arch/x86/include/asm/bug.h:93,
                    from include/linux/bug.h:5,
                    from include/linux/mmdebug.h:5,
                    from include/linux/percpu.h:5,
                    from include/linux/context_tracking_state.h:5,
                    from include/linux/hardirq.h:5,
                    from include/linux/kvm_host.h:7,
                    from arch/x86/kvm/x86.c:19:
   arch/x86/kvm/x86.c: In function 'kvm_dr6_fixed':
>> arch/x86/kvm/x86.c:1131:29: error: 'X86_FEATURE_BUS_LOCK_DETECT' undeclared (first use in this function); did you mean 'X86_FEATURE_SPLIT_LOCK_DETECT'?
    1131 |  if (!guest_cpuid_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT))
         |                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/compiler.h:58:52: note: in definition of macro '__trace_if_var'
      58 | #define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
         |                                                    ^~~~
   arch/x86/kvm/x86.c:1131:2: note: in expansion of macro 'if'
    1131 |  if (!guest_cpuid_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT))
         |  ^~
   arch/x86/kvm/x86.c:1131:29: note: each undeclared identifier is reported only once for each function it appears in
    1131 |  if (!guest_cpuid_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT))
         |                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/compiler.h:58:52: note: in definition of macro '__trace_if_var'
      58 | #define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
         |                                                    ^~~~
   arch/x86/kvm/x86.c:1131:2: note: in expansion of macro 'if'
    1131 |  if (!guest_cpuid_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT))
         |  ^~


vim +1131 arch/x86/kvm/x86.c

  1123	
  1124	static u64 kvm_dr6_fixed(struct kvm_vcpu *vcpu)
  1125	{
  1126		u64 fixed = DR6_FIXED_1;
  1127	
  1128		if (!guest_cpuid_has(vcpu, X86_FEATURE_RTM))
  1129			fixed |= DR6_RTM;
  1130	
> 1131		if (!guest_cpuid_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT))
  1132			fixed |= DR6_BUS_LOCK;
  1133		return fixed;
  1134	}
  1135	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
Paolo Bonzini Jan. 26, 2021, 4:31 p.m. UTC | #2 
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

>   
>   		/*
>   		 * 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;
>
Chenyi Qiang Jan. 27, 2021, 1:48 a.m. UTC | #3 
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;
>>
>
Xiaoyao Li Jan. 27, 2021, 3:41 a.m. UTC | #4 
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:

Paolo,

What do you want to convey with the new name DR6_ACTIVE_LOW? To be 
honest, the new name is confusing to me.

>> -        dr6 |= DR6_BD | DR6_RTM;
>> +        dr6 |= DR6_BD | DR6_RTM | DR6_BUS_LOCK;
> 
> dr6 |= DR6_BD | DR6_ACTIVE_LOW;
>
Paolo Bonzini Jan. 27, 2021, 10:04 a.m. UTC | #5 
On 27/01/21 04:41, Xiaoyao Li wrote:
> 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:
> 
> Paolo,
> 
> What do you want to convey with the new name DR6_ACTIVE_LOW? To be 
> honest, the new name is confusing to me.

"Active low" means that the bit is usually 1 and goes to 0 when the 
condition (such as RTM or bus lock) happens.  For almost all those DR6 
bits the value is in fact always 1, but if they are defined in the 
future it will require no code change.

Paolo

>>> -        dr6 |= DR6_BD | DR6_RTM;
>>> +        dr6 |= DR6_BD | DR6_RTM | DR6_BUS_LOCK;
>>
>> dr6 |= DR6_BD | DR6_ACTIVE_LOW;
>>
> 
>
Xiaoyao Li Jan. 28, 2021, 7:17 a.m. UTC | #6 
On 1/27/2021 6:04 PM, Paolo Bonzini wrote:
> On 27/01/21 04:41, Xiaoyao Li wrote:
>> 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:
>>
>> Paolo,
>>
>> What do you want to convey with the new name DR6_ACTIVE_LOW? To be 
>> honest, the new name is confusing to me.
> 
> "Active low" means that the bit is usually 1 and goes to 0 when the 
> condition (such as RTM or bus lock) happens.  For almost all those DR6 
> bits the value is in fact always 1, but if they are defined in the 
> future it will require no code change.

Why not keep use DR6_INIT, or DR6_RESET_VALUE? or any other better name.

It's just the default clear value of DR6 that no debug condition is hit.

> Paolo
> 
>>>> -        dr6 |= DR6_BD | DR6_RTM;
>>>> +        dr6 |= DR6_BD | DR6_RTM | DR6_BUS_LOCK;
>>>
>>> dr6 |= DR6_BD | DR6_ACTIVE_LOW;
>>>
>>
>>
>
Paolo Bonzini Jan. 28, 2021, 7:25 a.m. UTC | #7 
On 28/01/21 08:17, Xiaoyao Li wrote:
>>
>> "Active low" means that the bit is usually 1 and goes to 0 when the 
>> condition (such as RTM or bus lock) happens.  For almost all those DR6 
>> bits the value is in fact always 1, but if they are defined in the 
>> future it will require no code change.
> 
> Why not keep use DR6_INIT, or DR6_RESET_VALUE? or any other better name.
> 
> It's just the default clear value of DR6 that no debug condition is hit.

I preferred "DR6_ACTIVE_LOW" because the value is used only once or 
twice to initialize dr6, and many times to invert those bits.  For example:

vcpu->arch.dr6 &= ~DR_TRAP_BITS;
vcpu->arch.dr6 |= DR6_ACTIVE_LOW;
vcpu->arch.dr6 |= payload;
vcpu->arch.dr6 ^= payload & DR6_ACTIVE_LOW;

payload = vcpu->arch.dr6;
payload &= ~DR6_BT;
payload ^= DR6_ACTIVE_LOW;

The name conveys that it's not just the initialization value; it's also 
the XOR mask between the #DB exit qualification (which we also use as 
the "payload") and DR6.

Paolo
Xiaoyao Li Jan. 28, 2021, 7:41 a.m. UTC | #8 
On 1/28/2021 3:25 PM, Paolo Bonzini wrote:
> On 28/01/21 08:17, Xiaoyao Li wrote:
>>>
>>> "Active low" means that the bit is usually 1 and goes to 0 when the 
>>> condition (such as RTM or bus lock) happens.  For almost all those 
>>> DR6 bits the value is in fact always 1, but if they are defined in 
>>> the future it will require no code change.
>>
>> Why not keep use DR6_INIT, or DR6_RESET_VALUE? or any other better name.
>>
>> It's just the default clear value of DR6 that no debug condition is hit.
> 
> I preferred "DR6_ACTIVE_LOW" because the value is used only once or 
> twice to initialize dr6, and many times to invert those bits.  For example:
> 
> vcpu->arch.dr6 &= ~DR_TRAP_BITS;
> vcpu->arch.dr6 |= DR6_ACTIVE_LOW;
> vcpu->arch.dr6 |= payload;
> vcpu->arch.dr6 ^= payload & DR6_ACTIVE_LOW;
> 
> payload = vcpu->arch.dr6;
> payload &= ~DR6_BT;
> payload ^= DR6_ACTIVE_LOW;
> 
> The name conveys that it's not just the initialization value; it's also 
> the XOR mask between the #DB exit qualification (which we also use as 
> the "payload") and DR6.

Fair enough.
diff mbox series

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3ab7b46087b7..826fd1e87352 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -196,13 +196,14 @@  enum x86_intercept_stage;
 
 #define KVM_NR_DB_REGS	4
 
+#define DR6_BUS_LOCK   (1 << 11)
 #define DR6_BD		(1 << 13)
 #define DR6_BS		(1 << 14)
 #define DR6_BT		(1 << 15)
 #define DR6_RTM		(1 << 16)
-#define DR6_FIXED_1	0xfffe0ff0
+#define DR6_FIXED_1	0xfffe07f0
 #define DR6_INIT	0xffff0ff0
-#define DR6_VOLATILE	0x0001e00f
+#define DR6_VOLATILE	0x0001e80f
 
 #define DR7_BP_EN_MASK	0x000000ff
 #define DR7_GE		(1 << 9)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 56cae1ff9e3f..882598da20f0 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4327,7 +4327,7 @@  static int check_dr_read(struct x86_emulate_ctxt *ctxt)
 
 		ctxt->ops->get_dr(ctxt, 6, &dr6);
 		dr6 &= ~DR_TRAP_BITS;
-		dr6 |= DR6_BD | DR6_RTM;
+		dr6 |= DR6_BD | DR6_RTM | DR6_BUS_LOCK;
 		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,
 	 * 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;
 		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);
 
 	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;
 			}
 			*exit_qual = payload;
 		} else
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 75c9c6a0a3a4..13c9bcc4d9d9 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4824,7 +4824,8 @@  static int handle_exception_nmi(struct kvm_vcpu *vcpu)
 			kvm_queue_exception_p(vcpu, DB_VECTOR, dr6);
 			return 1;
 		}
-		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.dr7 = vmcs_readl(GUEST_DR7);
 		fallthrough;
 	case BP_VECTOR:
@@ -5068,7 +5069,8 @@  static int handle_dr(struct kvm_vcpu *vcpu)
 		 * guest debugging itself.
 		 */
 		if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) {
-			vcpu->run->debug.arch.dr6 = DR6_BD | DR6_RTM | DR6_FIXED_1;
+			vcpu->run->debug.arch.dr6 = DR6_BD | DR6_RTM | DR6_FIXED_1 |
+						    DR6_BUS_LOCK;
 			vcpu->run->debug.arch.dr7 = dr7;
 			vcpu->run->debug.arch.pc = kvm_get_linear_rip(vcpu);
 			vcpu->run->debug.arch.exception = DB_VECTOR;
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);
 
 		/*
 		 * 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;