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PCI: hv: Prepare hv_compose_msi_msg() for the VMBus-channel-interrupt-to-vCPU reassignment functionality

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The current implementation of hv_compose_msi_msg() is incompatible with
the new functionality that allows changing the vCPU a VMBus channel will
interrupt: if this function always calls hv_pci_onchannelcallback() in
the polling loop, the interrupt going to a different CPU could cause
hv_pci_onchannelcallback() to be running simultaneously in a tasklet,
which will break.  The current code also has a problem in that it is not
synchronized with vmbus_reset_channel_cb(): hv_compose_msi_msg() could
be accessing the ring buffer via the call of hv_pci_onchannelcallback()
well after the time that vmbus_reset_channel_cb() has finished.

Fix these issues as follows.  Disable the channel tasklet before
entering the polling loop in hv_compose_msi_msg() and re-enable it when
done.  This will prevent hv_pci_onchannelcallback() from running in a
tasklet on a different CPU.  Moreover, poll by always calling
hv_pci_onchannelcallback(), but check the channel callback function for
NULL and invoke the callback within a sched_lock critical section.  This
will prevent hv_compose_msi_msg() from accessing the ring buffer after
vmbus_reset_channel_cb() has acquired the sched_lock spinlock.

Suggested-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Andrew Murray <amurray@thegoodpenguin.co.uk>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: <linux-pci@vger.kernel.org>
Link: https://lore.kernel.org/r/20200406001514.19876-8-parri.andrea@gmail.com
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
This commit is contained in:
Andrea Parri (Microsoft) 2020-04-06 02:15:10 +02:00 committed by Wei Liu
parent 9403b66e61
commit 240ad77cb5
1 changed files with 28 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

42
drivers/pci/controller/pci-hyperv.c
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@ -1356,11 +1356,11 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
{
struct irq_cfg *cfg = irqd_cfg(data);
struct hv_pcibus_device *hbus;
struct vmbus_channel *channel;
struct hv_pci_dev *hpdev;
struct pci_bus *pbus;
struct pci_dev *pdev;
struct cpumask *dest;
unsigned long flags;
struct compose_comp_ctxt comp;
struct tran_int_desc *int_desc;
struct {
@ -1378,6 +1378,7 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
dest = irq_data_get_effective_affinity_mask(data);
pbus = pdev->bus;
hbus = container_of(pbus->sysdata, struct hv_pcibus_device, sysdata);
channel = hbus->hdev->channel;
hpdev = get_pcichild_wslot(hbus, devfn_to_wslot(pdev->devfn));
if (!hpdev)
goto return_null_message;
@ -1435,43 +1436,52 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
goto free_int_desc;
}
/*
* Prevents hv_pci_onchannelcallback() from running concurrently
* in the tasklet.
*/
tasklet_disable(&channel->callback_event);
/*
* Since this function is called with IRQ locks held, can't
* do normal wait for completion; instead poll.
*/
while (!try_wait_for_completion(&comp.comp_pkt.host_event)) {
unsigned long flags;
/* 0xFFFF means an invalid PCI VENDOR ID. */
if (hv_pcifront_get_vendor_id(hpdev) == 0xFFFF) {
dev_err_once(&hbus->hdev->device,
"the device has gone\n");
goto free_int_desc;
goto enable_tasklet;
}
/*
* When the higher level interrupt code calls us with
* interrupt disabled, we must poll the channel by calling
* the channel callback directly when channel->target_cpu is
* the current CPU. When the higher level interrupt code
* calls us with interrupt enabled, let's add the
* local_irq_save()/restore() to avoid race:
* hv_pci_onchannelcallback() can also run in tasklet.
* Make sure that the ring buffer data structure doesn't get
* freed while we dereference the ring buffer pointer. Test
* for the channel's onchannel_callback being NULL within a
* sched_lock critical section. See also the inline comments
* in vmbus_reset_channel_cb().
*/
local_irq_save(flags);
if (hbus->hdev->channel->target_cpu == smp_processor_id())
spin_lock_irqsave(&channel->sched_lock, flags);
if (unlikely(channel->onchannel_callback == NULL)) {
spin_unlock_irqrestore(&channel->sched_lock, flags);
goto enable_tasklet;
}
hv_pci_onchannelcallback(hbus);
local_irq_restore(flags);
spin_unlock_irqrestore(&channel->sched_lock, flags);
if (hpdev->state == hv_pcichild_ejecting) {
dev_err_once(&hbus->hdev->device,
"the device is being ejected\n");
goto free_int_desc;
goto enable_tasklet;
}
udelay(100);
}
tasklet_enable(&channel->callback_event);
if (comp.comp_pkt.completion_status < 0) {
dev_err(&hbus->hdev->device,
"Request for interrupt failed: 0x%x",
@ -1495,6 +1505,8 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
put_pcichild(hpdev);
return;
enable_tasklet:
tasklet_enable(&channel->callback_event);
free_int_desc:
kfree(int_desc);
drop_reference: