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Message-ID: <20241021045724.GB25279@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Sun, 20 Oct 2024 21:57:24 -0700
From: Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
To: Naman Jain <namjain@...ux.microsoft.com>
Cc: "K . Y . Srinivasan" <kys@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
John Starks <jostarks@...rosoft.com>, jacob.pan@...ux.microsoft.com,
Easwar Hariharan <eahariha@...ux.microsoft.com>
Subject: Re: [PATCH 1/2] Drivers: hv: vmbus: Wait for offers during boot
On Fri, Oct 18, 2024 at 04:58:10AM -0700, Naman Jain wrote:
> Channels offers are requested during vmbus initialization and resume
Nit: s/vmbus/VMBus
> from hibernation. Add support to wait for all channel offers to be
> delivered and processed before returning from vmbus_request_offers.
> This is to support user mode (VTL0) in OpenHCL (A Linux based
> paravisor for Confidential VMs) to ensure that all channel offers
> are present when init begins in VTL0, and it knows which channels
> the host has offered and which it has not.
Usermode isn't necessarily of VTL0, and this issue was actually identified
at a higher VTL in OpenHCL. However, this change isn't specific to OpenHCL,
but is intended for general use. I would prefer if the commit message were
either more generic or precisely aligned with the specific issue it's
addressing.
>
> This is in analogy to a PCI bus not returning from probe until it has
> scanned all devices on the bus.
>
> Without this, user mode can race with vmbus initialization and miss
> channel offers. User mode has no way to work around this other than
> sleeping for a while, since there is no way to know when vmbus has
> finished processing offers.
>
> With this added functionality, remove earlier logic which keeps track
> of count of offered channels post resume from hibernation. Once all
> offers delivered message is received, no further offers are going to
> be received. Consequently, logic to prevent suspend from happening
> after previous resume had missing offers, is also removed.
>
> Co-developed-by: John Starks <jostarks@...rosoft.com>
> Signed-off-by: John Starks <jostarks@...rosoft.com>
> Signed-off-by: Naman Jain <namjain@...ux.microsoft.com>
> ---
> drivers/hv/channel_mgmt.c | 38 +++++++++++++++++++++++---------------
> drivers/hv/connection.c | 4 ++--
> drivers/hv/hyperv_vmbus.h | 14 +++-----------
> drivers/hv/vmbus_drv.c | 16 ----------------
> 4 files changed, 28 insertions(+), 44 deletions(-)
>
> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> index 3c6011a48dab..ac514805dafe 100644
> --- a/drivers/hv/channel_mgmt.c
> +++ b/drivers/hv/channel_mgmt.c
> @@ -944,16 +944,6 @@ void vmbus_initiate_unload(bool crash)
> vmbus_wait_for_unload();
> }
>
> -static void check_ready_for_resume_event(void)
> -{
> - /*
> - * If all the old primary channels have been fixed up, then it's safe
> - * to resume.
> - */
> - if (atomic_dec_and_test(&vmbus_connection.nr_chan_fixup_on_resume))
> - complete(&vmbus_connection.ready_for_resume_event);
> -}
> -
> static void vmbus_setup_channel_state(struct vmbus_channel *channel,
> struct vmbus_channel_offer_channel *offer)
> {
> @@ -1109,8 +1099,6 @@ static void vmbus_onoffer(struct vmbus_channel_message_header *hdr)
>
> /* Add the channel back to the array of channels. */
> vmbus_channel_map_relid(oldchannel);
> - check_ready_for_resume_event();
> -
> mutex_unlock(&vmbus_connection.channel_mutex);
> return;
> }
> @@ -1297,12 +1285,11 @@ EXPORT_SYMBOL_GPL(vmbus_hvsock_device_unregister);
> /*
> * vmbus_onoffers_delivered -
> * This is invoked when all offers have been delivered.
> - *
> - * Nothing to do here.
> */
> static void vmbus_onoffers_delivered(
> struct vmbus_channel_message_header *hdr)
> {
> + complete(&vmbus_connection.all_offers_delivered_event);
> }
>
> /*
> @@ -1578,7 +1565,8 @@ void vmbus_onmessage(struct vmbus_channel_message_header *hdr)
> }
>
> /*
> - * vmbus_request_offers - Send a request to get all our pending offers.
> + * vmbus_request_offers - Send a request to get all our pending offers
> + * and wait for all offers to arrive.
> */
> int vmbus_request_offers(void)
> {
> @@ -1596,6 +1584,10 @@ int vmbus_request_offers(void)
>
> msg->msgtype = CHANNELMSG_REQUESTOFFERS;
>
> + /*
> + * This REQUESTOFFERS message will result in the host sending an all
> + * offers delivered message.
> + */
> ret = vmbus_post_msg(msg, sizeof(struct vmbus_channel_message_header),
> true);
>
> @@ -1607,6 +1599,22 @@ int vmbus_request_offers(void)
> goto cleanup;
> }
>
> + /* Wait for the host to send all offers. */
> + while (wait_for_completion_timeout(
> + &vmbus_connection.all_offers_delivered_event, msecs_to_jiffies(10 * 1000)) == 0) {
Nit: Can simply put 10000 instead of 10*1000
> + pr_warn("timed out waiting for all offers to be delivered...\n");
I know we are moving from async to sync, so earlier we never checked this.
But what if some channel timed out do we want to handle this case ? Or put
a comment why this is OK.
We could set error from here as well, but I see vmbus_request_offers return value
is never checked.
> + }
> +
> + /*
> + * Flush handling of offer messages (which may initiate work on
> + * other work queues).
> + */
> + flush_workqueue(vmbus_connection.work_queue);
> +
> + /* Flush processing the incoming offers. */
> + flush_workqueue(vmbus_connection.handle_primary_chan_wq);
> + flush_workqueue(vmbus_connection.handle_sub_chan_wq);
> +
> cleanup:
> kfree(msginfo);
>
> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
> index f001ae880e1d..8351360bba16 100644
> --- a/drivers/hv/connection.c
> +++ b/drivers/hv/connection.c
> @@ -34,8 +34,8 @@ struct vmbus_connection vmbus_connection = {
>
> .ready_for_suspend_event = COMPLETION_INITIALIZER(
> vmbus_connection.ready_for_suspend_event),
> - .ready_for_resume_event = COMPLETION_INITIALIZER(
> - vmbus_connection.ready_for_resume_event),
> + .all_offers_delivered_event = COMPLETION_INITIALIZER(
> + vmbus_connection.all_offers_delivered_event),
> };
> EXPORT_SYMBOL_GPL(vmbus_connection);
>
> diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
> index d2856023d53c..80cc65dac740 100644
> --- a/drivers/hv/hyperv_vmbus.h
> +++ b/drivers/hv/hyperv_vmbus.h
> @@ -287,18 +287,10 @@ struct vmbus_connection {
> struct completion ready_for_suspend_event;
>
> /*
> - * The number of primary channels that should be "fixed up"
> - * upon resume: these channels are re-offered upon resume, and some
> - * fields of the channel offers (i.e. child_relid and connection_id)
> - * can change, so the old offermsg must be fixed up, before the resume
> - * callbacks of the VSC drivers start to further touch the channels.
> + * Completed once the host has offered all channels. Note that
> + * some channels may still be being process on a work queue.
> */
> - atomic_t nr_chan_fixup_on_resume;
> - /*
> - * vmbus_bus_resume() waits for "nr_chan_fixup_on_resume" to
> - * drop to zero.
> - */
> - struct completion ready_for_resume_event;
> + struct completion all_offers_delivered_event;
> };
>
>
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 9b15f7daf505..bd3fc41dc06b 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -2427,11 +2427,6 @@ static int vmbus_bus_suspend(struct device *dev)
> if (atomic_read(&vmbus_connection.nr_chan_close_on_suspend) > 0)
> wait_for_completion(&vmbus_connection.ready_for_suspend_event);
>
> - if (atomic_read(&vmbus_connection.nr_chan_fixup_on_resume) != 0) {
> - pr_err("Can not suspend due to a previous failed resuming\n");
> - return -EBUSY;
> - }
> -
> mutex_lock(&vmbus_connection.channel_mutex);
>
> list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
> @@ -2456,17 +2451,12 @@ static int vmbus_bus_suspend(struct device *dev)
> pr_err("Sub-channel not deleted!\n");
> WARN_ON_ONCE(1);
> }
> -
> - atomic_inc(&vmbus_connection.nr_chan_fixup_on_resume);
> }
>
> mutex_unlock(&vmbus_connection.channel_mutex);
>
> vmbus_initiate_unload(false);
>
> - /* Reset the event for the next resume. */
> - reinit_completion(&vmbus_connection.ready_for_resume_event);
> -
> return 0;
> }
>
> @@ -2502,14 +2492,8 @@ static int vmbus_bus_resume(struct device *dev)
> if (ret != 0)
> return ret;
>
> - WARN_ON(atomic_read(&vmbus_connection.nr_chan_fixup_on_resume) == 0);
> -
> vmbus_request_offers();
>
> - if (wait_for_completion_timeout(
> - &vmbus_connection.ready_for_resume_event, 10 * HZ) == 0)
> - pr_err("Some vmbus device is missing after suspending?\n");
> -
> /* Reset the event for the next suspend. */
> reinit_completion(&vmbus_connection.ready_for_suspend_event);
>
> --
> 2.34.1
>
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