Re: [PATCH 3/8] KVM: PPC: booke: Added debug handler

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On 31.01.2013, at 18:08, Alexander Graf wrote:

> 
> On 31.01.2013, at 17:58, Bhushan Bharat-R65777 wrote:
> 
>> 
>> 
>>> -----Original Message-----
>>> From: Alexander Graf [mailto:agraf@xxxxxxx]
>>> Sent: Thursday, January 31, 2013 5:47 PM
>>> To: Bhushan Bharat-R65777
>>> Cc: kvm-ppc@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx
>>> Subject: Re: [PATCH 3/8] KVM: PPC: booke: Added debug handler
>>> 
>>> 
>>> On 30.01.2013, at 12:30, Bhushan Bharat-R65777 wrote:
>>> 
>>>> 
>>>> 
>>>>> -----Original Message-----
>>>>> From: Alexander Graf [mailto:agraf@xxxxxxx]
>>>>> Sent: Friday, January 25, 2013 5:13 PM
>>>>> To: Bhushan Bharat-R65777
>>>>> Cc: kvm-ppc@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; Bhushan
>>>>> Bharat-R65777
>>>>> Subject: Re: [PATCH 3/8] KVM: PPC: booke: Added debug handler
>>>>> 
>>>>> 
>>>>> On 16.01.2013, at 09:24, Bharat Bhushan wrote:
>>>>> 
>>>>>> From: Bharat Bhushan <Bharat.Bhushan@xxxxxxxxxxxxx>
>>>>>> 
>>>>>> Installed debug handler will be used for guest debug support and
>>>>>> debug facility emulation features (patches for these features will
>>>>>> follow this patch).
>>>>>> 
>>>>>> Signed-off-by: Liu Yu <yu.liu@xxxxxxxxxxxxx>
>>>>>> [bharat.bhushan@xxxxxxxxxxxxx: Substantial changes]
>>>>>> Signed-off-by: Bharat Bhushan <bharat.bhushan@xxxxxxxxxxxxx>
>>>>>> ---
>>>>>> arch/powerpc/include/asm/kvm_host.h |    1 +
>>>>>> arch/powerpc/kernel/asm-offsets.c   |    1 +
>>>>>> arch/powerpc/kvm/booke_interrupts.S |   49 ++++++++++++++++++++++++++++++---
>>> --
>>>>>> 3 files changed, 44 insertions(+), 7 deletions(-)
>>>>>> 
>>>>>> diff --git a/arch/powerpc/include/asm/kvm_host.h
>>>>>> b/arch/powerpc/include/asm/kvm_host.h
>>>>>> index 8a72d59..f4ba881 100644
>>>>>> --- a/arch/powerpc/include/asm/kvm_host.h
>>>>>> +++ b/arch/powerpc/include/asm/kvm_host.h
>>>>>> @@ -503,6 +503,7 @@ struct kvm_vcpu_arch {
>>>>>> 	u32 tlbcfg[4];
>>>>>> 	u32 mmucfg;
>>>>>> 	u32 epr;
>>>>>> +	u32 crit_save;
>>>>>> 	struct kvmppc_booke_debug_reg dbg_reg; #endif
>>>>>> 	gpa_t paddr_accessed;
>>>>>> diff --git a/arch/powerpc/kernel/asm-offsets.c
>>>>>> b/arch/powerpc/kernel/asm-offsets.c
>>>>>> index 46f6afd..02048f3 100644
>>>>>> --- a/arch/powerpc/kernel/asm-offsets.c
>>>>>> +++ b/arch/powerpc/kernel/asm-offsets.c
>>>>>> @@ -562,6 +562,7 @@ int main(void)
>>>>>> 	DEFINE(VCPU_LAST_INST, offsetof(struct kvm_vcpu, arch.last_inst));
>>>>>> 	DEFINE(VCPU_FAULT_DEAR, offsetof(struct kvm_vcpu, arch.fault_dear));
>>>>>> 	DEFINE(VCPU_FAULT_ESR, offsetof(struct kvm_vcpu, arch.fault_esr));
>>>>>> +	DEFINE(VCPU_CRIT_SAVE, offsetof(struct kvm_vcpu, arch.crit_save));
>>>>>> #endif /* CONFIG_PPC_BOOK3S */
>>>>>> #endif /* CONFIG_KVM */
>>>>>> 
>>>>>> diff --git a/arch/powerpc/kvm/booke_interrupts.S
>>>>>> b/arch/powerpc/kvm/booke_interrupts.S
>>>>>> index eae8483..dd9c5d4 100644
>>>>>> --- a/arch/powerpc/kvm/booke_interrupts.S
>>>>>> +++ b/arch/powerpc/kvm/booke_interrupts.S
>>>>>> @@ -52,12 +52,7 @@
>>>>>>                     (1<<BOOKE_INTERRUPT_PROGRAM) | \
>>>>>>                     (1<<BOOKE_INTERRUPT_DTLB_MISS))
>>>>>> 
>>>>>> -.macro KVM_HANDLER ivor_nr scratch srr0
>>>>>> -_GLOBAL(kvmppc_handler_\ivor_nr)
>>>>>> -	/* Get pointer to vcpu and record exit number. */
>>>>>> -	mtspr	\scratch , r4
>>>>>> -	mfspr   r4, SPRN_SPRG_THREAD
>>>>>> -	lwz     r4, THREAD_KVM_VCPU(r4)
>>>>>> +.macro __KVM_HANDLER ivor_nr scratch srr0
>>>>>> 	stw	r3, VCPU_GPR(R3)(r4)
>>>>>> 	stw	r5, VCPU_GPR(R5)(r4)
>>>>>> 	stw	r6, VCPU_GPR(R6)(r4)
>>>>>> @@ -74,6 +69,46 @@ _GLOBAL(kvmppc_handler_\ivor_nr)
>>>>>> 	bctr
>>>>>> .endm
>>>>>> 
>>>>>> +.macro KVM_HANDLER ivor_nr scratch srr0
>>>>>> +_GLOBAL(kvmppc_handler_\ivor_nr)
>>>>>> +	/* Get pointer to vcpu and record exit number. */
>>>>>> +	mtspr	\scratch , r4
>>>>>> +	mfspr   r4, SPRN_SPRG_THREAD
>>>>>> +	lwz     r4, THREAD_KVM_VCPU(r4)
>>>>>> +	__KVM_HANDLER \ivor_nr \scratch \srr0 .endm
>>>>>> +
>>>>>> +.macro KVM_DBG_HANDLER ivor_nr scratch srr0
>>>>>> +_GLOBAL(kvmppc_handler_\ivor_nr)
>>>>>> +	mtspr   \scratch, r4
>>>>>> +	mfspr	r4, SPRN_SPRG_THREAD
>>>>>> +	lwz	r4, THREAD_KVM_VCPU(r4)
>>>>>> +	stw	r3, VCPU_CRIT_SAVE(r4)
>>>>>> +	mfcr	r3
>>>>>> +	mfspr	r4, SPRN_CSRR1
>>>>>> +	andi.	r4, r4, MSR_PR
>>>>>> +	bne	1f
>>>>> 
>>>>> 
>>>>>> +	/* debug interrupt happened in enter/exit path */
>>>>>> +	mfspr   r4, SPRN_CSRR1
>>>>>> +	rlwinm  r4, r4, 0, ~MSR_DE
>>>>>> +	mtspr   SPRN_CSRR1, r4
>>>>>> +	lis	r4, 0xffff
>>>>>> +	ori	r4, r4, 0xffff
>>>>>> +	mtspr	SPRN_DBSR, r4
>>>>>> +	mfspr	r4, SPRN_SPRG_THREAD
>>>>>> +	lwz	r4, THREAD_KVM_VCPU(r4)
>>>>>> +	mtcr	r3
>>>>>> +	lwz     r3, VCPU_CRIT_SAVE(r4)
>>>>>> +	mfspr   r4, \scratch
>>>>>> +	rfci
>>>>> 
>>>>> What is this part doing? Try to ignore the debug exit?
>>>> 
>>>> As BOOKE doesn't have hardware support for virtualization, hardware never know
>>> current pc is in guest or in host.
>>>> So when enable hardware single step for guest, it cannot be disabled at the
>>> time guest exit. Thus, we'll see that an single step interrupt happens at the
>>> beginning of guest exit path.
>>>> 
>>>> With the above code we recognize this kind of single step interrupt disable
>>> single step and rfci.
>>>> 
>>>>> Why would we have MSR_DE
>>>>> enabled in the first place when we can't handle it?
>>>> 
>>>> When QEMU is using hardware debug resource then we always set MSR_DE during
>>> guest is running.
>>> 
>>> Right, but why is MSR_DE enabled during the exit path? If MSR_DE wasn't set, you
>>> wouldn't get a single step exit.
>> 
>> We always set MSR_DE in hw MSR when qemu using the debug resource.
> 
> In the _guest_ MSR, yes. But once we exit the guest, it shouldn't be set anymore, because we're in an interrupt handler, no? Or is MSR_DE kept alive on interrupts?

Ah, it's kept for non-debug interrupts. That explains things.


Alex

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