From: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx> Sent: Friday, April 16, 2021 7:35 AM
>
> Check that enough time has passed such that the modify channel message
> has been processed before taking a CPU offline.
>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx>
> ---
> drivers/hv/hv.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 53 insertions(+), 3 deletions(-)
>
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
> index 3e6ff83adff42..e0c522d143a37 100644
> --- a/drivers/hv/hv.c
> +++ b/drivers/hv/hv.c
> @@ -15,6 +15,7 @@
> #include <linux/hyperv.h>
> #include <linux/random.h>
> #include <linux/clockchips.h>
> +#include <linux/delay.h>
> #include <linux/interrupt.h>
> #include <clocksource/hyperv_timer.h>
> #include <asm/mshyperv.h>
> @@ -292,12 +293,50 @@ void hv_synic_disable_regs(unsigned int cpu)
> disable_percpu_irq(vmbus_irq);
> }
>
> +#define HV_MAX_TRIES 3
> +/*
> + * Scan the event flags page of 'this' CPU looking for any bit that is set. If we find one
> + * bit set, then wait for a few milliseconds. Repeat these steps for a maximum of 3 times.
> + * Return 'true', if there is still any set bit after this operation; 'false', otherwise.
> + *
> + * If a bit is set, that means there is a pending channel interrupt. The expectation is
> + * that the normal interrupt handling mechanism will find and process the channel interrupt
> + * "very soon", and in the process clear the bit.
> + */
> +static bool hv_synic_event_pending(void)
> +{
> + struct hv_per_cpu_context *hv_cpu = this_cpu_ptr(hv_context.cpu_context);
> + union hv_synic_event_flags *event =
> + (union hv_synic_event_flags *)hv_cpu->synic_event_page + VMBUS_MESSAGE_SINT;
> + unsigned long *recv_int_page = event->flags; /* assumes VMBus version >= VERSION_WIN8 */
> + bool pending;
> + u32 relid;
> + int tries = 0;
> +
> +retry:
> + pending = false;
> + for_each_set_bit(relid, recv_int_page, HV_EVENT_FLAGS_COUNT) {
> + /* Special case - VMBus channel protocol messages */
> + if (relid == 0)
> + continue;
> + pending = true;
> + break;
> + }
> + if (pending && tries++ < HV_MAX_TRIES) {
> + usleep_range(10000, 20000);
> + goto retry;
> + }
> + return pending;
> +}
>
> int hv_synic_cleanup(unsigned int cpu)
> {
> struct vmbus_channel *channel, *sc;
> bool channel_found = false;
>
> + if (vmbus_connection.conn_state != CONNECTED)
> + goto always_cleanup;
> +
> /*
> * Hyper-V does not provide a way to change the connect CPU once
> * it is set; we must prevent the connect CPU from going offline
> @@ -305,8 +344,7 @@ int hv_synic_cleanup(unsigned int cpu)
> * path where the vmbus is already disconnected, the CPU must be
> * allowed to shut down.
> */
> - if (cpu == VMBUS_CONNECT_CPU &&
> - vmbus_connection.conn_state == CONNECTED)
> + if (cpu == VMBUS_CONNECT_CPU)
> return -EBUSY;
>
> /*
> @@ -333,9 +371,21 @@ int hv_synic_cleanup(unsigned int cpu)
> }
> mutex_unlock(&vmbus_connection.channel_mutex);
>
> - if (channel_found && vmbus_connection.conn_state == CONNECTED)
> + if (channel_found)
> + return -EBUSY;
> +
> + /*
> + * channel_found == false means that any channels that were previously
> + * assigned to the CPU have been reassigned elsewhere with a call of
> + * vmbus_send_modifychannel(). Scan the event flags page looking for
> + * bits that are set and waiting with a timeout for vmbus_chan_sched()
> + * to process such bits. If bits are still set after this operation
> + * and VMBus is connected, fail the CPU offlining operation.
> + */
> + if (vmbus_proto_version >= VERSION_WIN10_V4_1 && hv_synic_event_pending())
> return -EBUSY;
>
> +always_cleanup:
> hv_stimer_legacy_cleanup(cpu);
>
> hv_synic_disable_regs(cpu);
> --
> 2.25.1
