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Re: [Qemu-devel] [Qemu-arm] [PATCH] target-arm: Fix translation level on

From: Sergey Fedorov
Subject: Re: [Qemu-devel] [Qemu-arm] [PATCH] target-arm: Fix translation level on early translation faults
Date: Thu, 3 Mar 2016 19:37:17 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1

On 03.03.2016 17:55, Peter Maydell wrote:
> On 3 March 2016 at 14:48, Sergey Fedorov <address@hidden> wrote:
>> On 03.03.2016 16:49, Peter Maydell wrote:
>>> On 2 March 2016 at 19:19, Sergey Fedorov <address@hidden> wrote:
>>>> On 02.03.2016 21:04, Sergey Sorokin wrote:
>>>>> Qemu reports translation fault on 1st level instead of 0th level in case 
>>>>> of
>>>>> AArch64 address translation if the translation table walk is disabled or
>>>>> the address is in the gap between the two regions.
>>>> It's probably not a very clear description in the commit message. IIUC,
>>>> level 0 fault is reported in case of any fault from TTBR in AArch64 state.
>>> Yes (though you mean "under an AArch64 translation regime"). Conversely, the
>>> only fault reported at level 0 under an AArch32 translation regime is
>>> the AddressSize fault (for bad addresses in TTBR0/1), which we don't
>>> currently implement.
>>> There's also a code path later in the function that does
>>>     level = va_size == 64 ? 0 : 1;
>>> but I'm not sure it's worth rearranging that code to avoid the
>>> duplication of "what level do we report this kind of fault at?".
>> Right, but actually I think this patch is going to fix the two "goto
>> do_fault" cases which can happen before this "level = va_size == 64 ? 0
>> : 1", namely the EDP check and the check for virtual address which is in
>> the gap between TTBR0 and TTBR1 regions.
> Yes, this patch is definitely fixing a bug; I'm just mentioning that other
> code path because it seems to be the result of previously fixing the bug
> for a particular special case...

Ah, right, I think I understand you :) So we'd better remove these lines:

            /* AArch64 reports these as level 0 faults.
             * AArch32 reports these as level 1 faults.
            level = va_size == 64 ? 0 : 1;
            fault_type = translation_fault;

Kind regards,

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