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Re: [PATCH v1 3/9] hw/intc/gic: use MxTxAttrs to divine accessing CPU


From: mads
Subject: Re: [PATCH v1 3/9] hw/intc/gic: use MxTxAttrs to divine accessing CPU
Date: Mon, 26 Sep 2022 13:20:54 +0200

>>> On 22 Sep 2022, at 16.58, Alex Bennée <alex.bennee@linaro.org> wrote:
>>> 
>>> Now that MxTxAttrs encodes a CPU we should use that to figure it out.
>>> This solves edge cases like accessing via gdbstub or qtest.
>>> 
>>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>>> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/124
>>> 
>>> ---
>>> v2
>>> - update for new field
>>> - bool asserts
>>> ---
>>> hw/intc/arm_gic.c | 39 ++++++++++++++++++++++-----------------
>>> 1 file changed, 22 insertions(+), 17 deletions(-)
>>> 
>>> diff --git a/hw/intc/arm_gic.c b/hw/intc/arm_gic.c
>>> index 492b2421ab..b58d3c4a95 100644
>>> --- a/hw/intc/arm_gic.c
>>> +++ b/hw/intc/arm_gic.c
>>> @@ -56,17 +56,22 @@ static const uint8_t gic_id_gicv2[] = {
>>>    0x04, 0x00, 0x00, 0x00, 0x90, 0xb4, 0x2b, 0x00, 0x0d, 0xf0, 0x05, 0xb1
>>> };
>>> 
>>> -static inline int gic_get_current_cpu(GICState *s)
>>> +static inline int gic_get_current_cpu(GICState *s, MemTxAttrs attrs)
>>> {
>>> -    if (!qtest_enabled() && s->num_cpu > 1) {
>>> -        return current_cpu->cpu_index;
>>> -    }
>>> -    return 0;
>>> +    /*
>>> +     * Something other than a CPU accessing the GIC would be a bug as
>>> +     * would a CPU index higher than the GICState expects to be
>>> +     * handling
>>> +     */
>>> +    g_assert(attrs.requester_is_cpu);
>>> +    g_assert(attrs.cpu_index < s->num_cpu);
>>> +
>>> +    return attrs.requester_id;
>>> }
>> 
>> The asserts here abort on macOS, with HVF accelerator:
>> 
>> ERROR:../hw/intc/arm_gic.c:66:gic_get_current_cpu: assertion failed: 
>> (attrs.requester_is_cpu)
>> Bail out! ERROR:../hw/intc/arm_gic.c:66:gic_get_current_cpu: assertion 
>> failed: (attrs.requester_is_cpu)
>> 
>> If I revert the changes inside this function, it seemingly works
>> again.
> 
> Thanks for testing.
> 
> I guess this is because the we have a soft GIC for HVF. Somewhere in the
> hvf code path we must encode up an MemTxAttrs when the gic is accessed.
> 
> Could you try in the EC_DATAABORT path in
> target/arm/hvf/hvf.c:hvf_vcpu_exec:
> 
>        if (iswrite) {
>            val = hvf_get_reg(cpu, srt);
>            address_space_write(&address_space_memory,
>                                hvf_exit->exception.physical_address,
>                                MEMTXATTRS_CPU(cpu->cpu_index), &val, len);
>        } else {
>            address_space_read(&address_space_memory,
>                               hvf_exit->exception.physical_address,
>                               MEMTXATTRS_CPU(cpu->cpu_index), &val, len);
>            hvf_set_reg(cpu, srt, val);
>        }
> 
> if that works I'll cook up a proper patch.
> 
> -- 
> Alex Bennée

Perfect. This fixes the issue.




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