[PATCH v2] KVM: PPC: Exit guest upon fatal machine check exception

[Aravinda Prasad]

On Thursday 17 December 2015 08:02 AM, David Gibson wrote:
> On Wed, Dec 16, 2015 at 11:26:12AM +0530, Aravinda Prasad wrote:
>> This patch modifies KVM to cause a guest exit with
>> KVM_EXIT_NMI instead of immediately delivering a 0x200
>> interrupt to guest upon machine check exception in
>> guest address. Exiting the guest enables QEMU to build
>> error log and deliver machine check exception to guest
>> OS (either via guest OS registered machine check
>> handler or via 0x200 guest OS interrupt vector).
>>
>> 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 patched 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:
>>
>> https://lists.nongnu.org/archive/html/qemu-devel/2014-11/msg00813.html
>>
>> This patch also introduces a new KVM capability to
>> control how KVM behaves on machine check exception.
>> Without this capability, KVM redirects machine check
>> exceptions to guest's 0x200 vector if the address in
>> error belongs to guest. With this capability KVM
>> causes a guest exit with NMI exit reason.
>>
>> This is required to avoid problems if a new kernel/KVM
>> is used with an old QEMU for guests that don't issue
>> "ibm,nmi-register". As old QEMU does not understand the
>> NMI exit type, it treats it as a fatal error. However,
>> the guest could have handled the machine check error
>> if the exception was delivered to guest's 0x200 interrupt
>> vector instead of NMI exit in case of old QEMU.
>>
>> Change Log v2:
>>   - Added KVM capability
>>
>> Signed-off-by: Aravinda Prasad <aravinda at linux.vnet.ibm.com>
>> ---
>>  arch/powerpc/include/asm/kvm_host.h     |    1 +
>>  arch/powerpc/kernel/asm-offsets.c       |    1 +
>>  arch/powerpc/kvm/book3s_hv.c            |   12 +++-------
>>  arch/powerpc/kvm/book3s_hv_rmhandlers.S |   37 +++++++++++++++----------------
>>  arch/powerpc/kvm/powerpc.c              |    7 ++++++
>>  include/uapi/linux/kvm.h                |    1 +
>>  6 files changed, 31 insertions(+), 28 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
>> index 827a38d..8a652ba 100644
>> --- a/arch/powerpc/include/asm/kvm_host.h
>> +++ b/arch/powerpc/include/asm/kvm_host.h
>> @@ -243,6 +243,7 @@ struct kvm_arch {
>>  	int hpt_cma_alloc;
>>  	struct dentry *debugfs_dir;
>>  	struct dentry *htab_dentry;
>> +	u8 fwnmi_enabled;
>>  #endif /* CONFIG_KVM_BOOK3S_HV_POSSIBLE */
>>  #ifdef CONFIG_KVM_BOOK3S_PR_POSSIBLE
>>  	struct mutex hpt_mutex;
>> diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
>> index 221d584..6a4e81a 100644
>> --- a/arch/powerpc/kernel/asm-offsets.c
>> +++ b/arch/powerpc/kernel/asm-offsets.c
>> @@ -506,6 +506,7 @@ int main(void)
>>  	DEFINE(KVM_ENABLED_HCALLS, offsetof(struct kvm, arch.enabled_hcalls));
>>  	DEFINE(KVM_LPCR, offsetof(struct kvm, arch.lpcr));
>>  	DEFINE(KVM_VRMA_SLB_V, offsetof(struct kvm, arch.vrma_slb_v));
>> +	DEFINE(KVM_FWNMI, offsetof(struct kvm, arch.fwnmi_enabled));
>>  	DEFINE(VCPU_DSISR, offsetof(struct kvm_vcpu, arch.shregs.dsisr));
>>  	DEFINE(VCPU_DAR, offsetof(struct kvm_vcpu, arch.shregs.dar));
>>  	DEFINE(VCPU_VPA, offsetof(struct kvm_vcpu, arch.vpa.pinned_addr));
>> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
>> index 2280497..1b1dff0 100644
>> --- a/arch/powerpc/kvm/book3s_hv.c
>> +++ b/arch/powerpc/kvm/book3s_hv.c
>> @@ -859,15 +859,9 @@ static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
>>  		r = RESUME_GUEST;
>>  		break;
>>  	case BOOK3S_INTERRUPT_MACHINE_CHECK:
>> -		/*
>> -		 * Deliver a machine check interrupt to the guest.
>> -		 * We have to do this, even if the host has handled the
>> -		 * machine check, because machine checks use SRR0/1 and
>> -		 * the interrupt might have trashed guest state in them.
>> -		 */
>> -		kvmppc_book3s_queue_irqprio(vcpu,
>> -					    BOOK3S_INTERRUPT_MACHINE_CHECK);
>> -		r = RESUME_GUEST;
>> +		/* Exit to guest with KVM_EXIT_NMI as exit reason */
>> +		run->exit_reason = KVM_EXIT_NMI;
>> +		r = RESUME_HOST;
>>  		break;
>>  	case BOOK3S_INTERRUPT_PROGRAM:
>>  	{
>> diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> index b98889e..f43c124 100644
>> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> @@ -147,7 +147,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
>>  	addi	r1, r1, 112
>>  	ld	r7, HSTATE_HOST_MSR(r13)
>>
> 
> Seems like the comment a little above this should be updated to
> reflect the fact that this path no longer handles machine checks.
> 
> Apart from that and the access width bug Thomas spotted, it looks ok
> to me,.

sure.

Regards,
Aravinda

> 
> 
> 
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-- 
Regards,
Aravinda