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

From: Peter Maydell
Subject: Re: [Qemu-devel] [Qemu-arm] [PATCH] target-arm: Fix translation level on early translation faults
Date: Thu, 3 Mar 2016 14:55:36 +0000

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...

-- PMM

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