linux-kernel - RE: [PATCH v2] Drivers: hv: vmbus: Don't assign VMbus channel interrupts to isolated CPUs

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Message-ID: <MW2PR2101MB10354159598C83FF6EF6777ACCD89@MW2PR2101MB1035.namprd21.prod.outlook.com>
Date:   Fri, 27 May 2022 15:41:26 +0000
From:   Stephen Hemminger <sthemmin@...rosoft.com>
To:     Saurabh Sengar <ssengar@...ux.microsoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Saurabh Singh Sengar <ssengar@...rosoft.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Subject: RE: [PATCH v2] Drivers: hv: vmbus: Don't assign VMbus channel
 interrupts to isolated CPUs

Would this have impact for DPDK applications using isolated cpus?

-----Original Message-----
From: Saurabh Sengar <ssengar@...ux.microsoft.com> 
Sent: Friday, May 27, 2022 12:22 AM
To: KY Srinivasan <kys@...rosoft.com>; Haiyang Zhang <haiyangz@...rosoft.com>; Stephen Hemminger <sthemmin@...rosoft.com>; wei.liu@...nel.org; Dexuan Cui <decui@...rosoft.com>; linux-hyperv@...r.kernel.org; linux-kernel@...r.kernel.org; Saurabh Singh Sengar <ssengar@...rosoft.com>; Michael Kelley (LINUX) <mikelley@...rosoft.com>
Subject: [PATCH v2] Drivers: hv: vmbus: Don't assign VMbus channel interrupts to isolated CPUs

When initially assigning a VMbus channel interrupt to a CPU, don’t choose
a managed IRQ isolated CPU (as specified on the kernel boot line with
parameter 'isolcpus=managed_irq,<#cpu>'). Also, when using sysfs to change
the CPU that a VMbus channel will interrupt, don't allow changing to a
managed IRQ isolated CPU.

Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
---
v2: * better commit message
    * Added back empty line, removed by mistake
    * Removed error print for sysfs error

 drivers/hv/channel_mgmt.c | 18 ++++++++++++------
 drivers/hv/vmbus_drv.c    |  4 ++++
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 97d8f56..e1fe029 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -21,6 +21,7 @@
 #include <linux/cpu.h>
 #include <linux/hyperv.h>
 #include <asm/mshyperv.h>
+#include <linux/sched/isolation.h>
 
 #include "hyperv_vmbus.h"
 
@@ -728,16 +729,20 @@ static void init_vp_index(struct vmbus_channel *channel)
 	u32 i, ncpu = num_online_cpus();
 	cpumask_var_t available_mask;
 	struct cpumask *allocated_mask;
+	const struct cpumask *hk_mask = housekeeping_cpumask(HK_TYPE_MANAGED_IRQ);
 	u32 target_cpu;
 	int numa_node;
 
 	if (!perf_chn ||
-	    !alloc_cpumask_var(&available_mask, GFP_KERNEL)) {
+	    !alloc_cpumask_var(&available_mask, GFP_KERNEL) ||
+	    cpumask_empty(hk_mask)) {
 		/*
 		 * If the channel is not a performance critical
 		 * channel, bind it to VMBUS_CONNECT_CPU.
 		 * In case alloc_cpumask_var() fails, bind it to
 		 * VMBUS_CONNECT_CPU.
+		 * If all the cpus are isolated, bind it to
+		 * VMBUS_CONNECT_CPU.
 		 */
 		channel->target_cpu = VMBUS_CONNECT_CPU;
 		if (perf_chn)
@@ -758,17 +763,19 @@ static void init_vp_index(struct vmbus_channel *channel)
 		}
 		allocated_mask = &hv_context.hv_numa_map[numa_node];
 
-		if (cpumask_equal(allocated_mask, cpumask_of_node(numa_node))) {
+retry:
+		cpumask_xor(available_mask, allocated_mask, cpumask_of_node(numa_node));
+		cpumask_and(available_mask, available_mask, hk_mask);
+
+		if (cpumask_empty(available_mask)) {
 			/*
 			 * We have cycled through all the CPUs in the node;
 			 * reset the allocated map.
 			 */
 			cpumask_clear(allocated_mask);
+			goto retry;
 		}
 
-		cpumask_xor(available_mask, allocated_mask,
-			    cpumask_of_node(numa_node));
-
 		target_cpu = cpumask_first(available_mask);
 		cpumask_set_cpu(target_cpu, allocated_mask);
 
@@ -778,7 +785,6 @@ static void init_vp_index(struct vmbus_channel *channel)
 	}
 
 	channel->target_cpu = target_cpu;
-
 	free_cpumask_var(available_mask);
 }
 
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 714d549..547ae33 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -21,6 +21,7 @@
 #include <linux/kernel_stat.h>
 #include <linux/clockchips.h>
 #include <linux/cpu.h>
+#include <linux/sched/isolation.h>
 #include <linux/sched/task_stack.h>
 
 #include <linux/delay.h>
@@ -1770,6 +1771,9 @@ static ssize_t target_cpu_store(struct vmbus_channel *channel,
 	if (target_cpu >= nr_cpumask_bits)
 		return -EINVAL;
 
+	if (!cpumask_test_cpu(target_cpu, housekeeping_cpumask(HK_TYPE_MANAGED_IRQ)))
+		return -EINVAL;
+
 	/* No CPUs should come up or down during this. */
 	cpus_read_lock();
 
-- 
1.8.3.1