Re: [PATCH v3 6/9] KVM: arm/arm64: Limit icache invalidation to prefetch aborts

[Marc Zyngier <marc.zyngier@arm.com>]

On Wed, Nov 01 2017 at 11:17:27 am GMT, Andrew Jones <drjones@redhat.com> wrote:
> On Mon, Oct 23, 2017 at 05:11:19PM +0100, Marc Zyngier wrote:
>> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
>> index 2174244f6317..0417c8e2a81c 100644
>> --- a/virt/kvm/arm/mmu.c
>> +++ b/virt/kvm/arm/mmu.c
>> @@ -1292,7 +1292,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>  			  unsigned long fault_status)
>>  {
>>  	int ret;
>> -	bool write_fault, writable, hugetlb = false, force_pte = false;
>> +	bool write_fault, exec_fault, writable, hugetlb = false, force_pte = false;
>>  	unsigned long mmu_seq;
>>  	gfn_t gfn = fault_ipa >> PAGE_SHIFT;
>>  	struct kvm *kvm = vcpu->kvm;
>> @@ -1304,7 +1304,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>  	unsigned long flags = 0;
>>  
>>  	write_fault = kvm_is_write_fault(vcpu);
>> -	if (fault_status == FSC_PERM && !write_fault) {
>> +	exec_fault = kvm_vcpu_trap_is_iabt(vcpu);
>> +	VM_BUG_ON(write_fault && exec_fault);
>
> This VM_BUG_ON can never fire as long as kvm_is_write_fault() is
> defined as
>
>  {
>    if (kvm_vcpu_trap_is_iabt(vcpu))
>        return false;
>    return kvm_vcpu_dabt_iswrite(vcpu);
>  }

That's indeed what I expect. But given that the code now relies on this
property, I chose to make it explicit.

Or are you seeing a better way of making this an invariant?

Thanks,

	M.
-- 
Jazz is not dead, it just smell funny.