[PATCH v3 2/2] KVM: PPC: Exit guest upon MCE when FWNMI capability is enabled
Aravinda Prasad
aravinda at linux.vnet.ibm.com
Mon Jan 25 19:39:30 AEDT 2016
On Sunday 24 January 2016 02:54 AM, Paul Mackerras wrote:
> On Sat, Jan 23, 2016 at 06:23:35PM +0530, Aravinda Prasad wrote:
>>
>>
>> On Saturday 23 January 2016 03:58 PM, Paul Mackerras wrote:
>>> On Wed, Jan 13, 2016 at 12:38:09PM +0530, Aravinda Prasad wrote:
>>>> Enhance KVM to cause a guest exit with KVM_EXIT_NMI
>>>> exit reasons upon a machine check exception (MCE) in
>>>> the guest address space if the KVM_CAP_PPC_FWNMI
>>>> capability is enabled (instead of delivering 0x200
>>>> interrupt to guest). This enables QEMU to build error
>>>> log and deliver machine check exception to guest via
>>>> guest registered machine check handler.
>>>>
>>>> This approach simplifies the delivering of machine
>>>> check exception to guest OS compared to the earlier
>>>> approach of KVM directly invoking 0x200 guest interrupt
>>>> vector. In the earlier approach QEMU was enhanced to
>>>> patch the 0x200 interrupt vector during boot. The
>>>> patched code at 0x200 issued a private hcall to pass
>>>> the control to QEMU to build the error log.
>>>>
>>>> This design/approach is based on the feedback for the
>>>> QEMU patches to handle machine check exception. Details
>>>> of earlier approach of handling machine check exception
>>>> in QEMU and related discussions can be found at:
>>>
>>> [snip]
>>>
>>>> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>>>> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>>>> @@ -133,21 +133,18 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
>>>> stb r0, HSTATE_HWTHREAD_REQ(r13)
>>>>
>>>> /*
>>>> - * For external and machine check interrupts, we need
>>>> - * to call the Linux handler to process the interrupt.
>>>> - * We do that by jumping to absolute address 0x500 for
>>>> - * external interrupts, or the machine_check_fwnmi label
>>>> - * for machine checks (since firmware might have patched
>>>> - * the vector area at 0x200). The [h]rfid at the end of the
>>>> - * handler will return to the book3s_hv_interrupts.S code.
>>>> - * For other interrupts we do the rfid to get back
>>>> - * to the book3s_hv_interrupts.S code here.
>>>> + * For external interrupts we need to call the Linux
>>>> + * handler to process the interrupt. We do that by jumping
>>>> + * to absolute address 0x500 for external interrupts.
>>>> + * The [h]rfid at the end of the handler will return to
>>>> + * the book3s_hv_interrupts.S code. For other interrupts
>>>> + * we do the rfid to get back to the book3s_hv_interrupts.S
>>>> + * code here.
>>>> */
>>>> ld r8, 112+PPC_LR_STKOFF(r1)
>>>> addi r1, r1, 112
>>>> ld r7, HSTATE_HOST_MSR(r13)
>>>>
>>>> - cmpwi cr1, r12, BOOK3S_INTERRUPT_MACHINE_CHECK
>>>> cmpwi r12, BOOK3S_INTERRUPT_EXTERNAL
>>>> beq 11f
>>>> cmpwi r12, BOOK3S_INTERRUPT_H_DOORBELL
>>>> @@ -162,7 +159,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
>>>> mtmsrd r6, 1 /* Clear RI in MSR */
>>>> mtsrr0 r8
>>>> mtsrr1 r7
>>>> - beq cr1, 13f /* machine check */
>>>> RFI
>>>>
>>>> /* On POWER7, we have external interrupts set to use HSRR0/1 */
>>>> @@ -170,8 +166,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
>>>> mtspr SPRN_HSRR1, r7
>>>> ba 0x500
>>>>
>>>> -13: b machine_check_fwnmi
>>>> -
>>>
>>> So, what you're disabling here is the host-side handling of the
>>> machine check after completing the guest->host switch. This has
>>> nothing to do with how the machine check gets communicated to the
>>> guest.
>>>
>>> Now, part of the host-side machine check handling has already
>>> happened, but I thought there was more that was done in host kernel
>>> virtual mode. If this change really is needed then I would want an
>>> ack from Mahesh that this is correct, and it will need to be explained
>>> in detail in the patch description.
>>
>> If we don't do that we will end up running into
>> panic() in opal_machine_check() if UE belonged to guest.
>>
>> Details in this link:
>> http://marc.info/?l=kvm-ppc&m=144730552720044&w=2
>
> Well maybe the panic call needs to be changed. But the way you have
> it, we *never* get to opal_machine_check for any machine check
> interrupt, and I have a hard time believing that is correct.
If I am not wrong, earlier, even without this patch we never get to
opal_machine_check() from this place for the machine check happening
inside the guest (irrespective of whether the machine check is recovered
or not). Because, we jump to fast_interrupt_c_return() from
machine_check_realmode without causing the guest to exit.
With this patch I call mc_cont from machine_check_realmode and want the
guest to exit with NMI exit code. However, we don't want to call
opal_machine_check(), because if we call opal_machine_check() we don't
end up with NMI exit for the guest.
Regards,
Aravinda
>
> Paul.
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>
--
Regards,
Aravinda
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