Re: [Qemu-devel] [PULL 04/32] target/riscv: Implement riscv_cpu_unassigned_access

[Palmer Dabbelt <palmer@sifive.com>]

On Tue, 17 Sep 2019 09:37:47 PDT (-0700), alistair23@gmail.com wrote:
> On Tue, Sep 17, 2019 at 6:56 AM Peter Maydell <peter.maydell@linaro.org> wrote:
>>
>> On Fri, 16 Aug 2019 at 09:57, Peter Maydell <peter.maydell@linaro.org> wrote:
>> >
>> > On Thu, 15 Aug 2019 at 23:17, Palmer Dabbelt <palmer@sifive.com> wrote:
>> > > You're more than welcome to take them over.  I've got something that boots
>> > > Linux on my unassigned_access branch (github.com/palmer-dabbelt/qemu), but I
>> > > haven't sanitized the whole port for physical accesses and I haven't convinced
>> > > myself that my hook implementation is correct.
>> >
>> > Rather than doing
>> >    if (retaddr) {
>> >        cpu_restore_state(cs, retaddr, true);
>> >    }
>> >
>> > at the start of the hook I think you just want to pass 'retaddr'
>> > as the final argument to riscv_raise_exception() instead of
>> > using GETPC(). Other than that I think the hook itself is right.
>> >
>> > The 'git grep' regexes in docs/devel/loads-stores.rst are handy
>> > for finding the places where the target code is doing physical
>> > accesses. IIRC the only ones I found with a quick scan were the
>> > PTE loads in get_physical_address() via ldl_phys/ldq_phys, which will
>> > now return 0 and run into the 'invalid PTE' code path. I don't
>> > know whether your architecture requires some different behaviour
>> > for bus errors on page table walk than that (you might want to
>> > specifically code the error path anyway or comment it even if the
>> > behaviour is right, to be a bit more explicit that it can happen).
>>
>> Gentle ping -- would somebody like to have a go at the riscv
>> do_transaction_failed hook conversion? I think it should be
>> straightforward, and riscv is now the only architecture still
>> using the old unassigned_access hook and preventing us from
>> getting rid of it entirely.
>
> Thanks for the ping Peter, I forgot about this.
>
> @Palmer I have taken your patches, made some changes based on Peter's
> comments and rebased them on your PR branch.
>
> I'll double check, but the hook implementation looks correct and I
> can't see any other obvious unsanitised physical accesses so it should
> be ok. I'll send them out today if I don't find any issues.

Thanks!

>
> Alistair
>
>>
>> thanks
>> -- PMM