On 05.02.2018 21:57, Collin L. Walling wrote:
> It is possible while waiting for multiple types of external
> interrupts that we might have pending irqs remaining between
> irq consumption and irq disabling. Those interrupts could
> propagate to the guest after IPL completes and cause unwanted
> behavior.
>
> To avoid this, we clear the write event mask to prevent further
> service interrupts from ASCII events and then consume all pending
> irqs for a miniscule duration. Once finished, we reset the write
> event mask and resume business as usual.
>
> Signed-off-by: Collin L. Walling <wall...@linux.vnet.ibm.com>
> ---
> pc-bios/s390-ccw/menu.c | 16 ++++++++++++++++
> pc-bios/s390-ccw/sclp.c | 12 ++++++++++++
> 2 files changed, 28 insertions(+)
>
> diff --git a/pc-bios/s390-ccw/menu.c b/pc-bios/s390-ccw/menu.c
> index 85d285f..971f6b6 100644
> --- a/pc-bios/s390-ccw/menu.c
> +++ b/pc-bios/s390-ccw/menu.c
> @@ -64,6 +64,20 @@ static inline bool check_clock_int(void)
> return *code == 0x1004;
> }
>
> +static void clear_pending_irqs(void)
> +{
> + uint64_t time = 50 * TOD_CLOCK_SECOND / 0x3e8;
s/0x3e8/1000/ please.
> + sclp_clear_write_mask();
> +
> + set_clock_comparator(get_clock() + time);
> + enable_clock_int();
> + consume_sclp_int();
> + disable_clock_int();
> +
> + sclp_setup(); /* re-enable write mask */
> +}
I'm pretty much confused by this code. First, isn't there a small chance
that there is a clock int between consume_sclp_int() and
disable_clock_int() (if consume_sclp_int() has consumed an SCLP
interrupt instead of a clock interrupt) ?
Second, if you finally enable the SCLP write mask again, doesn't that
mean that there could be interrupts pending again afterwards?
Thomas
