Re: [PATCH kvmtool 06/21] hw/i8042: Refactor trap handler

Alexandru Elisei
2021-02-18T12:37:33Z

Hi Andre,

On 2/18/21 10:34 AM, Andre Przywara wrote:
> On Thu, 11 Feb 2021 17:23:13 +0000
> Alexandru Elisei <alexandru.elisei@arm.com> wrote:
>
>> Hi Andre,
>>
>> On 12/10/20 2:28 PM, Andre Przywara wrote:
>>> With the planned retirement of the special ioport emulation code, we
>>> need to provide an emulation function compatible with the MMIO
>>> prototype.
>>>
>>> Adjust the trap handler to use that new function, and provide shims to
>>> implement the old ioport interface, for now.
>>>
>>> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>>> ---
>>> hw/i8042.c | 68 +++++++++++++++++++++++++++---------------------------
>>> 1 file changed, 34 insertions(+), 34 deletions(-)
>>>
>>> diff --git a/hw/i8042.c b/hw/i8042.c
>>> index 36ee183f..eb1f9d28 100644
>>> --- a/hw/i8042.c
>>> +++ b/hw/i8042.c
>>> @@ -292,52 +292,52 @@ static void kbd_reset(void)
>>> };
>>> }
>>>
>>> -/*
>>> - * Called when the OS has written to one of the keyboard's ports (0x60 or 0x64)
>>> - */
>>> -static bool kbd_in(struct ioport *ioport, struct kvm_cpu *vcpu, u16 port, void *data, int size)
>>> +static void kbd_io(struct kvm_cpu *vcpu, u64 addr, u8 *data, u32 len,
>>> + u8 is_write, void *ptr)
>>> {
>>> - switch (port) {
>>> - case I8042_COMMAND_REG: {
>>> - u8 value = kbd_read_status();
>>> - ioport__write8(data, value);
>>> + u8 value;
>>> +
>>> + if (is_write)
>>> + value = ioport__read8(data);
>>> +
>>> + switch (addr) {
>>> + case I8042_COMMAND_REG:
>>> + if (is_write)
>>> + kbd_write_command(vcpu->kvm, value);
>>> + else
>>> + value = kbd_read_status();
>>> break;
>>> - }
>>> - case I8042_DATA_REG: {
>>> - u8 value = kbd_read_data();
>>> - ioport__write8(data, value);
>>> + case I8042_DATA_REG:
>>> + if (is_write)
>>> + kbd_write_data(value);
>>> + else
>>> + value = kbd_read_data();
>>> break;
>>> - }
>>> - case I8042_PORT_B_REG: {
>>> - ioport__write8(data, 0x20);
>>> + case I8042_PORT_B_REG:
>>> + if (!is_write)
>>> + value = 0x20;
>>> break;
>>> - }
>>> default:
>>> - return false;
>>> + return;
>> Any particular reason for removing the false return value? I don't see it
>> mentioned in the commit message. Otherwise this is identical to the two functions
>> it replaces.
> Because the MMIO handler prototype is void, in contrast to the PIO one.
> Since on returning "false" we only seem to panic kvmtool, this is of
> quite limited use, I'd say.

Actually, in ioport.c::kvm__emulate_io(), if kvm->cfg.ioport_debug is true, it
will print an error and then panic in kvm_cpu__start(); otherwise the error is
silently ignored. serial.c is another device where an unknown register returns
false. In rtc.c, the unknown register is ignored. cfi_flash.c prints debugging
information. So I guess kvmtool implements all possible methods of handling an
unknown register *at the same time*, so it's up to you how you want to handle it.

>>> }
>>>
>>> + if (!is_write)
>>> + ioport__write8(data, value);
>>> +}
>>> +
>>> +/*
>>> + * Called when the OS has written to one of the keyboard's ports (0x60 or 0x64)
>>> + */
>>> +static bool kbd_in(struct ioport *ioport, struct kvm_cpu *vcpu, u16 port, void *data, int size)
>>> +{
>>> + kbd_io(vcpu, port, data, size, false, NULL);
>> is_write is an u8, not a bool.
> Right, will fix this.
>
>> I never could wrap my head around the ioport convention of "in" (read) and "out"
>> (write). To be honest, changing is_write changed to an enum so it's crystal clear
>> what is happening would help with that a lot, but I guess that's a separate patch.
> "in" and "out" are the x86 assembly mnemonics, but it's indeed
> confusing, because the device side has a different view (CPU "in" means
> pushing data "out" of the device). I usually look at the code to see
> what it's actually meant to do.
> So yeah, I feel like a lot of those device emulations could use
> some update. but that's indeed something for another day.

Agreed.

Thanks,

Alex

>
> Cheers,
> Andre
>
>>> +
>>> return true;
>>> }
>>>
>>> static bool kbd_out(struct ioport *ioport, struct kvm_cpu *vcpu, u16 port, void *data, int size)
>>> {
>>> - switch (port) {
>>> - case I8042_COMMAND_REG: {
>>> - u8 value = ioport__read8(data);
>>> - kbd_write_command(vcpu->kvm, value);
>>> - break;
>>> - }
>>> - case I8042_DATA_REG: {
>>> - u8 value = ioport__read8(data);
>>> - kbd_write_data(value);
>>> - break;
>>> - }
>>> - case I8042_PORT_B_REG: {
>>> - break;
>>> - }
>>> - default:
>>> - return false;
>>> - }
>>> + kbd_io(vcpu, port, data, size, true, NULL);
>>>
>>> return true;
>>> }