On 1 August 2024 22:07:25 BST, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>On Thu, Aug 01 2024 at 16:22, David Woodhouse wrote:
>> On Thu, 2024-08-01 at 10:00 +0100, David Woodhouse wrote:
>> bool __init pit_timer_init(void)
>> {
>> - if (!use_pit())
>> + if (!use_pit()) {
>> + if (!hypervisor_is_type(X86_HYPER_NATIVE)) {
>> + /*
>> + * Don't just ignore the PIT. Ensure it's stopped,
>> + * because VMMs otherwise steal CPU time just to
>> + * pointlessly waggle the (masked) IRQ.
>> + */
>> + raw_spin_lock(&i8253_lock);
>> + outb_p(0x30, PIT_MODE);
>> +
>> + /*
>> + * It's not entirely clear from the datasheet, but some
>> + * virtual implementations don't stop until the counter
>> + * is actually written.
>> + */
>> + if (i8253_clear_counter_on_shutdown) {
>> + outb_p(0, PIT_CH0);
>> + outb_p(0, PIT_CH0);
>> + }
>> + raw_spin_unlock(&i8253_lock);
>> + }
>> return false;
>> + }
>
>That's just wrong. What we want is to have the underlying problem
>fixed in the driver and then make:
>
>> clockevent_i8253_init(true);
>
>bool clockevent_i8253_init(bool enable, bool oneshot);
>
>so it can invoke the shutdown sequence instead of registering the pile:
>
> if (!enable) {
> shutdown();
> return false;
> }
> ...
> return true;
>
>and the call site becomes:
>
> if (!clockevent_i8253_init(use_pit(), true))
> return false;
>
>No?
Yes. Well, kind of. The way I actually did it was by exposing the shutdown function instead of an "init" function which optionally did the opposite. But yes, I left the hardware-bashing in precisely once place, in the driver.
