Re: [RFC PATCH 5/8] qtest/libqos: Restrict CPU I/O instructions

[Laszlo Ersek <lersek@redhat.com>]

On 03/16/21 16:55, Philippe Mathieu-Daudé wrote:
> Hi Richard and Laszlo,
> 
> On 3/16/21 4:43 PM, Richard Henderson wrote:
>> On 3/16/21 9:37 AM, Laszlo Ersek wrote:
>>> (+Peter, comment below)
>>>
>>> On 03/15/21 00:29, Philippe Mathieu-Daudé wrote:
>>>> Restrict CPU I/O instructions to architectures providing
>>>> I/O bus.
>>>>
>>>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>>>> ---
>>>>   tests/qtest/libqos/fw_cfg.h | 3 +++
>>>>   tests/qtest/libqos/fw_cfg.c | 2 ++
>>>>   2 files changed, 5 insertions(+)
>>>>
>>>> diff --git a/tests/qtest/libqos/fw_cfg.h b/tests/qtest/libqos/fw_cfg.h
>>>> index c6a7cf8cf05..3bfb6d6d55b 100644
>>>> --- a/tests/qtest/libqos/fw_cfg.h
>>>> +++ b/tests/qtest/libqos/fw_cfg.h
>>>> @@ -36,6 +36,8 @@ size_t qfw_cfg_get_file(QFWCFG *fw_cfg, const char
>>>> *filename,
>>>>     QFWCFG *mm_fw_cfg_init(QTestState *qts, uint64_t base);
>>>>   void mm_fw_cfg_uninit(QFWCFG *fw_cfg);
>>>> +
>>>> +#ifdef TARGET_HAS_IOPORT
>>>>   QFWCFG *io_fw_cfg_init(QTestState *qts, uint16_t base);
>>>>   void io_fw_cfg_uninit(QFWCFG *fw_cfg);
>>>>   @@ -48,6 +50,7 @@ static inline void pc_fw_cfg_uninit(QFWCFG *fw_cfg)
>>>>   {
>>>>       io_fw_cfg_uninit(fw_cfg);
>>>>   }
>>>> +#endif /* TARGET_HAS_IOPORT */
>>>>     G_DEFINE_AUTOPTR_CLEANUP_FUNC(QFWCFG, mm_fw_cfg_uninit)
>>>>   diff --git a/tests/qtest/libqos/fw_cfg.c b/tests/qtest/libqos/fw_cfg.c
>>>> index 6b8e1babe51..db2b83f5212 100644
>>>> --- a/tests/qtest/libqos/fw_cfg.c
>>>> +++ b/tests/qtest/libqos/fw_cfg.c
>>>> @@ -131,6 +131,7 @@ void mm_fw_cfg_uninit(QFWCFG *fw_cfg)
>>>>       g_free(fw_cfg);
>>>>   }
>>>>   +#ifdef TARGET_HAS_IOPORT
>>>>   static void io_fw_cfg_select(QFWCFG *fw_cfg, uint16_t key)
>>>>   {
>>>>       qtest_outw(fw_cfg->qts, fw_cfg->base, key);
>>>> @@ -162,3 +163,4 @@ void io_fw_cfg_uninit(QFWCFG *fw_cfg)
>>>>   {
>>>>       g_free(fw_cfg);
>>>>   }
>>>> +#endif /* TARGET_HAS_IOPORT */
>>>>
>>>
>>> I'm not sure the macro name is ideal; the PCI host on aarch64/"virt"
>>> emulates IO Ports (it's possible to allocate PCI IO resources on
>>> "virt"). From patch#3, TARGET_HAS_IOPORT does not seem to extend to
>>> arm64.
>>
>> Correct, aarch64 has memory-mapped pci io resources, they are not on a
>> separate ioport address space as for x86 and avr.
> 
> I first wrote TARGET_CPU_HAS_IOPORT but realized architecture
> and CPU are linked, so I elided _CPU_.
> 
> What I'd like to clear from the QTest API is the idea that the CPU has
> direct access to the I/O bus via I/O specific instructions.
> 
> Any machine able to use a host <-> PCI bus chipset is able to access
> the I/O function from the PCI bus.
> 
> The fact that on X86 the first PCI function is wired to the same I/O
> bus than the CPU is a machine implementation detail.
> 
> When accessing PCI I/O ressources on Aarch64, you don't have to use
> dedicated I/O instructions.
> 
> Anyway for now Thomas discarded this series, as QTest is a generic API,
> and we never had to worry about mixing address spaces so far, so not in
> a hurry to clean this (although it would be useful to change address
> space to access DMA or secure-CPU-view from QTest).

If this is about an "IO Bus" or "IO instructions", then we should call
the macro TARGET_HAS_IO_BUS or "TARGET_ISA_HAS_IO" (or
"TARGET_HAS_IO_INSNS"), or something like those. My only confusion was
about the "IO Port" expression in the macro name; the idea is OK from my
perspective otherwise.

Thanks
Laszlo