Skip to contentSkip to conversation

Drivers: hv: vmbus: Allow cleanup of VMBUS_CONNECT_CPU if disconnected

PATCH Applied Chris Co 3 participants 3 messages Nov 10, 2020 – Nov 11, 2020

Subsystems (2)
Hyper-V/Azure core and drivers Microsoft MANA RDMA driver
lore
Share & tools
lore

Chris Co

author
#0 lore raw

PATCH 1/1 Drivers: hv: vmbus: Allow cleanup of VMBUS_CONNECT_CPU if disconnected

From: Chris Co <[email protected]>

When invoking kexec() on a Linux guest running on a Hyper-V host, the kernel panics.

    RIP: 0010:cpuhp_issue_call+0x137/0x140
    Call Trace:
    __cpuhp_remove_state_cpuslocked+0x99/0x100
    __cpuhp_remove_state+0x1c/0x30
    hv_kexec_handler+0x23/0x30 [hv_vmbus]
    hv_machine_shutdown+0x1e/0x30
    machine_shutdown+0x10/0x20
    kernel_kexec+0x6d/0x96
    __do_sys_reboot+0x1ef/0x230
    __x64_sys_reboot+0x1d/0x20
    do_syscall_64+0x6b/0x3d8
    entry_SYSCALL_64_after_hwframe+0x44/0xa9

This was due to hv_synic_cleanup() callback returning -EBUSY to cpuhp_issue_call() when tearing down the VMBUS_CONNECT_CPU, even if the vmbus_connection.conn_state = DISCONNECTED. hv_synic_cleanup() should succeed in the case where vmbus_connection.conn_state is DISCONNECTED.

Fix is to add an extra condition to test for vmbus_connection.conn_state == CONNECTED on the VMBUS_CONNECT_CPU and only return early if true. This way the kexec() path can still shut everything down while preserving the initial behavior of preventing CPU offlining on the VMBUS_CONNECT_CPU while the VM is running.

Fixes 8a857c55420f29 ("Drivers: hv: vmbus: Always handle the VMBus messages on CPU0")
Signed-off-by Chris Co <[email protected]>
Cc [email protected]
---
 drivers/hv/hv.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
drivers/hv/hv.c +6 -2
index 0cde10fe0e71..f202ac7f4b3d 100644
@@ -244,9 +244,13 @@ int hv_synic_cleanup(unsigned int cpu)
 
 	/*
 	 * 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.
+	 * it is set; we must prevent the connect CPU from going offline
+	 * while the VM is running normally. But in the panic or kexec()
+	 * path where the vmbus is already disconnected, the CPU must be
+	 * allowed to shut down.
 	 */
-	if (cpu == VMBUS_CONNECT_CPU)
+	if (cpu == VMBUS_CONNECT_CPU &&
+	    vmbus_connection.conn_state == CONNECTED)
 		return -EBUSY;
 
 	/*
Signature · 1 line
2.17.1
Reviewed-by on v1 1/1
#1 lore raw
Quoted 30 lines · Chris Co

From: Chris Co <[email protected]>

When invoking kexec() on a Linux guest running on a Hyper-V host, the kernel panics.

    RIP: 0010:cpuhp_issue_call+0x137/0x140
    Call Trace:
    __cpuhp_remove_state_cpuslocked+0x99/0x100
    __cpuhp_remove_state+0x1c/0x30
    hv_kexec_handler+0x23/0x30 [hv_vmbus]
    hv_machine_shutdown+0x1e/0x30
    machine_shutdown+0x10/0x20
    kernel_kexec+0x6d/0x96
    __do_sys_reboot+0x1ef/0x230
    __x64_sys_reboot+0x1d/0x20
    do_syscall_64+0x6b/0x3d8
    entry_SYSCALL_64_after_hwframe+0x44/0xa9

This was due to hv_synic_cleanup() callback returning -EBUSY to cpuhp_issue_call() when tearing down the VMBUS_CONNECT_CPU, even if the vmbus_connection.conn_state = DISCONNECTED. hv_synic_cleanup() should succeed in the case where vmbus_connection.conn_state is DISCONNECTED.

Fix is to add an extra condition to test for vmbus_connection.conn_state == CONNECTED on the VMBUS_CONNECT_CPU and only return early if true. This way the kexec() path can still shut everything down while preserving the initial behavior of preventing CPU offlining on the VMBUS_CONNECT_CPU while the VM is running.

Quoted 3 lines
Fixes 8a857c55420f29 ("Drivers: hv: vmbus: Always handle the VMBus messages on CPU0")
Signed-off-by Chris Co <[email protected]>
Cc [email protected]
Reviewed-by Andrea Parri (Microsoft) <[email protected]>

Thanks,
Andrea

Quoted 27 lines
---
 drivers/hv/hv.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
drivers/hv/hv.c +6 -2
index 0cde10fe0e71..f202ac7f4b3d 100644
@@ -244,9 +244,13 @@ int hv_synic_cleanup(unsigned int cpu)
 
 	/*
 	 * 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.
+	 * it is set; we must prevent the connect CPU from going offline
+	 * while the VM is running normally. But in the panic or kexec()
+	 * path where the vmbus is already disconnected, the CPU must be
+	 * allowed to shut down.
 	 */
-	if (cpu == VMBUS_CONNECT_CPU)
+	if (cpu == VMBUS_CONNECT_CPU &&
+	    vmbus_connection.conn_state == CONNECTED)
 		return -EBUSY;
 
 	/*
Signature · 1 line
2.17.1
maintainer Applied
#2 lore raw
Quoted 31 lines · Andrea Parri
Quoted 30 lines · Chris Co

From: Chris Co <[email protected]>

When invoking kexec() on a Linux guest running on a Hyper-V host, the kernel panics.

    RIP: 0010:cpuhp_issue_call+0x137/0x140
    Call Trace:
    __cpuhp_remove_state_cpuslocked+0x99/0x100
    __cpuhp_remove_state+0x1c/0x30
    hv_kexec_handler+0x23/0x30 [hv_vmbus]
    hv_machine_shutdown+0x1e/0x30
    machine_shutdown+0x10/0x20
    kernel_kexec+0x6d/0x96
    __do_sys_reboot+0x1ef/0x230
    __x64_sys_reboot+0x1d/0x20
    do_syscall_64+0x6b/0x3d8
    entry_SYSCALL_64_after_hwframe+0x44/0xa9

This was due to hv_synic_cleanup() callback returning -EBUSY to cpuhp_issue_call() when tearing down the VMBUS_CONNECT_CPU, even if the vmbus_connection.conn_state = DISCONNECTED. hv_synic_cleanup() should succeed in the case where vmbus_connection.conn_state is DISCONNECTED.

Fix is to add an extra condition to test for vmbus_connection.conn_state == CONNECTED on the VMBUS_CONNECT_CPU and only return early if true. This way the kexec() path can still shut everything down while preserving the initial behavior of preventing CPU offlining on the VMBUS_CONNECT_CPU while the VM is running.

Quoted 5 lines
Quoted 3 lines
Fixes 8a857c55420f29 ("Drivers: hv: vmbus: Always handle the VMBus messages on CPU0")
Signed-off-by Chris Co <[email protected]>
Cc [email protected]
Reviewed-by Andrea Parri (Microsoft) <[email protected]>

Applied to hyperv-fixes. Thanks Chris and Andrea.

Wei.