Re: [PATCH V3 10/10] arm64: KVM: add guest SEA support

[Punit Agrawal <punit.agrawal@arm.com>]

"Baicar, Tyler" <tbaicar@codeaurora.org> writes:

> Hello Punit,
>
> On 10/13/2016 7:14 AM, Punit Agrawal wrote:
>> Hi Tyler,
>>
>> I know I've had my last comment already ;), but I thought I'd rather
>> raise the question than stay confused...
>>
>> Tyler Baicar <tbaicar@codeaurora.org> writes:
>>
>>> Currently external aborts are unsupported by the guest abort
>>> handling. Add handling for SEAs so that the host kernel reports
>>> SEAs which occur in the guest kernel.
>>>
>>> Signed-off-by: Tyler Baicar <tbaicar@codeaurora.org>
>>> ---
>>>   arch/arm/include/asm/kvm_arm.h       |  1 +
>>>   arch/arm/include/asm/system_misc.h   |  5 +++++
>>>   arch/arm/kvm/mmu.c                   | 15 +++++++++++++--
>>>   arch/arm64/include/asm/kvm_arm.h     |  1 +
>>>   arch/arm64/include/asm/system_misc.h |  2 ++
>>>   arch/arm64/mm/fault.c                | 13 +++++++++++++
>>>   6 files changed, 35 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/arm/include/asm/kvm_arm.h b/arch/arm/include/asm/kvm_arm.h
>>> index e22089f..33a77509 100644
>>> --- a/arch/arm/include/asm/kvm_arm.h
>>> +++ b/arch/arm/include/asm/kvm_arm.h
>>> @@ -187,6 +187,7 @@
>>>   #define FSC_FAULT	(0x04)
>>>   #define FSC_ACCESS	(0x08)
>>>   #define FSC_PERM	(0x0c)
>>> +#define FSC_EXTABT	(0x10)
>>>     /* Hyp Prefetch Fault Address Register (HPFAR/HDFAR) */
>>>   #define HPFAR_MASK	(~0xf)
>>> diff --git a/arch/arm/include/asm/system_misc.h b/arch/arm/include/asm/system_misc.h
>>> index a3d61ad..86e1faa 100644
>>> --- a/arch/arm/include/asm/system_misc.h
>>> +++ b/arch/arm/include/asm/system_misc.h
>>> @@ -24,4 +24,9 @@ extern unsigned int user_debug;
>>>     #endif /* !__ASSEMBLY__ */
>>>   +inline int handle_guest_sea(unsigned long addr, unsigned int
>>> esr)
>>> +{
>>> +	return -1;
>>> +}
>>> +
>>>   #endif /* __ASM_ARM_SYSTEM_MISC_H */
>>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>>> index e9a5c0e..24cde84 100644
>>> --- a/arch/arm/kvm/mmu.c
>>> +++ b/arch/arm/kvm/mmu.c
>>> @@ -29,6 +29,7 @@
>>>   #include <asm/kvm_asm.h>
>>>   #include <asm/kvm_emulate.h>
>>>   #include <asm/virt.h>
>>> +#include <asm/system_misc.h>
>>>     #include "trace.h"
>>>   @@ -1441,8 +1442,18 @@ int kvm_handle_guest_abort(struct kvm_vcpu
>>> *vcpu, struct kvm_run *run)
>>>     	/* Check the stage-2 fault is trans. fault or write fault */
>>>   	fault_status = kvm_vcpu_trap_get_fault_type(vcpu);
>>> -	if (fault_status != FSC_FAULT && fault_status != FSC_PERM &&
>>> -	    fault_status != FSC_ACCESS) {
>>> +
>>> +	if (fault_status == FSC_EXTABT) {
>>> +		if(handle_guest_sea((unsigned long)fault_ipa,
>>> +				    kvm_vcpu_get_hsr(vcpu))) {
>>> +			kvm_err("Failed to handle guest SEA, FSC: EC=%#x xFSC=%#lx ESR_EL2=%#lx\n",
>>> +				kvm_vcpu_trap_get_class(vcpu),
>>> +				(unsigned long)kvm_vcpu_trap_get_fault(vcpu),
>>> +				(unsigned long)kvm_vcpu_get_hsr(vcpu));
>>> +			return -EFAULT;
>>> +		}
>>> +	} else if (fault_status != FSC_FAULT && fault_status != FSC_PERM &&
>>> +		   fault_status != FSC_ACCESS) {
>>>   		kvm_err("Unsupported FSC: EC=%#x xFSC=%#lx ESR_EL2=%#lx\n",
>>>   			kvm_vcpu_trap_get_class(vcpu),
>>>   			(unsigned long)kvm_vcpu_trap_get_fault(vcpu),
>>> diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
>>> index 4b5c977..be0efb6 100644
>>> --- a/arch/arm64/include/asm/kvm_arm.h
>>> +++ b/arch/arm64/include/asm/kvm_arm.h
>>> @@ -201,6 +201,7 @@
>>>   #define FSC_FAULT	ESR_ELx_FSC_FAULT
>>>   #define FSC_ACCESS	ESR_ELx_FSC_ACCESS
>>>   #define FSC_PERM	ESR_ELx_FSC_PERM
>>> +#define FSC_EXTABT	ESR_ELx_FSC_EXTABT
>>>     /* Hyp Prefetch Fault Address Register (HPFAR/HDFAR) */
>>>   #define HPFAR_MASK	(~UL(0xf))
>>> diff --git a/arch/arm64/include/asm/system_misc.h b/arch/arm64/include/asm/system_misc.h
>>> index 90daf4a..8522fff 100644
>>> --- a/arch/arm64/include/asm/system_misc.h
>>> +++ b/arch/arm64/include/asm/system_misc.h
>>> @@ -77,4 +77,6 @@ extern void (*arm_pm_restart)(enum reboot_mode reboot_mode, const char *cmd);
>>>   int sea_register_handler_chain(struct notifier_block *nb);
>>>   void sea_unregister_handler_chain(struct notifier_block *nb);
>>>   +int handle_guest_sea(unsigned long addr, unsigned int esr);
>>> +
>>>   #endif	/* __ASM_SYSTEM_MISC_H */
>>> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>>> index 81cb7ad..d714432 100644
>>> --- a/arch/arm64/mm/fault.c
>>> +++ b/arch/arm64/mm/fault.c
>>> @@ -597,6 +597,19 @@ static const char *fault_name(unsigned int esr)
>>>   }
>>>     /*
>>> + * Handle Synchronous External Aborts that occur in a guest kernel.
>>> + */
>>> +int handle_guest_sea(unsigned long addr, unsigned int esr)
>>> +{
>>> +	atomic_notifier_call_chain(&sea_handler_chain, 0, NULL);
>>> +
>>> +	pr_err("Synchronous External Abort: %s (0x%08x) at 0x%016lx\n",
>>> +		fault_name(esr), esr, addr);
>>> +
>>> +	return 0;
>>> +}
>> Don't we need to pass the abort to the guest?
> This requires some infrastructure to implement virtual "ACPI platform
> error interface" to expose the details of the abort to the guest. This
> patchset does not cover that and focuses on feature parity with other
> architectures that support APEI. There are discussions among Linaro
> partners about how this can be achieved in the long term, but that
> work is outside the scope of this patchset. This patch will ensure
> that if a guest encounters one of these errors then it will be
> reported before getting killed. Before this patch we would just get an
> unsupported FSC print out and then the guest would be killed.

OK.

I think we might be talking about different things though.

I am referring to the injection of the synchronous external abort into
the guest - similar to what's been done for prefetch abort in the
kvm_guest_handle_abort.

Maybe there is no benefit in passing the abort to the guest. In that
case, can you please add a comment where you handle external abort
(FSC_EXTABT) in kvm_guest_handle_abort.

>
> Thanks,
> Tyler
>>
>> Thanks,
>> Punit
>>
>>> +
>>> +/*
>>>    * Dispatch a data abort to the relevant handler.
>>>    */
>>>   asmlinkage void __exception do_mem_abort(unsigned long addr, unsigned int esr,