Re: [Qemu-devel] [PATCH 09/16] target-arm: Support multiple address spaces in page table walks

[Paolo Bonzini <pbonzini@redhat.com>]

On 09/11/2015 11:58, Peter Maydell wrote:
> On 9 November 2015 at 10:51, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>
>>
>> On 05/11/2015 19:15, Peter Maydell wrote:
>>> If we have a secure address space, use it in page table walks:
>>>  * when doing the physical accesses to read descriptors,
>>>    make them through the correct address space
>>>  * when the final result indicates a secure access, pass the
>>>    correct address space index to tlb_set_page_with_attrs()
>>>
>>> (The descriptor reads are the only direct physical accesses
>>> made in target-arm/ for CPUs which might have TrustZone.)
>>
>> What is the case where you have no secure address space and you have
>> TrustZone?  KVM doesn't have TrustZone, so it should never be in a
>> secure regime, should it?
> 
> You mean "what is the case where is_secure but cpu->num_ases == 1" ?
> That happens if you have a TrustZone CPU but the board has only
> connected up one address space, because there is no difference
> in the view from Secure and NonSecure. (vexpress is like this
> in hardware, and most of our board models for TZ CPUS are like
> that now even if the real h/w makes a distinction.)
> 
> I could have handled that by making the CPU init code always
> register two ASes (using the same one twice if the board code
> only passes one or using system_address_space twice if the
> board code doesn't pass one at all), but that seemed a bit wasteful.

I think it's simpler though.  Complicating the init code is better than
handling the condition throughout all the helpers...

Paolo