Re: [Qemu-devel] [PATCH] target/xtensa: convert to do_transaction_failed

[Peter Maydell]

On 24 August 2018 at 19:10, Max Filippov <address@hidden> wrote:
> Hi Peter,
>
> On Fri, Aug 24, 2018 at 10:56 AM, Peter Maydell
> <address@hidden> wrote:
>> On 20 August 2018 at 03:31, Max Filippov <address@hidden> wrote:
>>> Signed-off-by: Max Filippov <address@hidden>
>>> ---
>>>  target/xtensa/cpu.c       |  2 +-
>>>  target/xtensa/cpu.h       |  7 ++++---
>>>  target/xtensa/op_helper.c | 12 +++++++-----
>>>  3 files changed, 12 insertions(+), 9 deletions(-)
>>
>> Hi -- thanks for doing this conversion. This change means that
>> you'll no longer get guest exceptions for bus errors that happen
>> during get_pte()'s page table entry fetch. Don't you need at
>> least a TODO comment there indicating that there's missing
>> behaviour?
>
> Thanks for taking a look and letting me know, I've missed that entirely.

Basically the new hook only handles failures for code
paths that go via the MMU; anything where the target code
does a direct physical address lookup has to handle the
failure itself. I think for xtensa that's just the page
table reads.

(This is why it's a bit of a pain to convert a target,
but the end result makes much more sense, because almost
always the target code doing physical address accesses
doesn't want to handle bus errors by randomly longjumping out.)

thanks
-- PMM