Re: [PATCH V7 10/10] arm/arm64: KVM: add guest SEA support

["Baicar, Tyler" <tbaicar@codeaurora.org>]

Hello Marc,


On 1/16/2017 4:58 AM, Marc Zyngier wrote:
> Hi Tyler,
>
> On 12/01/17 18:15, Tyler Baicar wrote:
>> 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                   | 18 ++++++++++++++++--
>>   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, 38 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..ea45d94 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__ */
>>   
>> +static 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..1152966 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 +1442,21 @@ 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) {
>> +
>> +	/* The host kernel will handle the synchronous external abort. There
>> +	 * is no need to pass the error into the guest.
>> +	 */
>> +	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));
> So there's one thing I don't like here, which is that we just gave the
> guest a very nice way to pollute the host's kernel log with spurious
> messages. So I'd rather make it silent, or at the very least rate limited.
Before this patch, if a guest exits with FSC_EXTABT, then the below 
print for
"Unsupported FSC..." would happen. So this print isn't really adding any 
noise
that isn't already there. Also, this print would only happen if 
handle_guest_sea
fails. If you still think this print should be removed then I will 
remove it though.
>> +			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 e7f3440..27816cb 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 register_sea_notifier(struct notifier_block *nb);
>>   void unregister_sea_notifier(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 81039c7..fa8d4d7 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);
> Same here.
I will remove this print.
>> +
>> +	return 0;
>> +}
>> +
>> +/*
>>    * Dispatch a data abort to the relevant handler.
>>    */
>>   asmlinkage void __exception do_mem_abort(unsigned long addr, unsigned int esr,
>>
> Thanks,
>
> 	M.
Thanks,
Tyler

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