Commit f02a6769 authored May 18, 2023 by Michael Kelley Committed by Greg Kroah-Hartman Jun 28, 2023

Drivers: hv: vmbus: Fix vmbus_wait_for_unload() to scan present CPUs

commit 320805ab61e5f1e2a5729ae266e16bec2904050c upstream.

vmbus_wait_for_unload() may be called in the panic path after other
CPUs are stopped. vmbus_wait_for_unload() currently loops through
online CPUs looking for the UNLOAD response message. But the values of
CONFIG_KEXEC_CORE and crash_kexec_post_notifiers affect the path used
to stop the other CPUs, and in one of the paths the stopped CPUs
are removed from cpu_online_mask. This removal happens in both
x86/x64 and arm64 architectures. In such a case, vmbus_wait_for_unload()
only checks the panic'ing CPU, and misses the UNLOAD response message
except when the panic'ing CPU is CPU 0. vmbus_wait_for_unload()
eventually times out, but only after waiting 100 seconds.

Fix this by looping through *present* CPUs in vmbus_wait_for_unload().
The cpu_present_mask is not modified by stopping the other CPUs in the
panic path, nor should it be.

Also, in a CoCo VM the synic_message_page is not allocated in
hv_synic_alloc(), but is set and cleared in hv_synic_enable_regs()
and hv_synic_disable_regs() such that it is set only when the CPU is
online. If not all present CPUs are online when vmbus_wait_for_unload()
is called, the synic_message_page might be NULL. Add a check for this.

Fixes: cd95aad5 ("Drivers: hv: vmbus: handle various crash scenarios")
Cc: stable@vger.kernel.org
Reported-by: John Starks <jostarks@microsoft.com>
Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/1684422832-38476-1-git-send-email-mikelley@microsoft.com

Signed-off-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 966708ed

drivers/hv/channel_mgmt.c

+16 −2

Original line number	Diff line number	Diff line
		@@ -802,11 +802,22 @@ static void vmbus_wait_for_unload(void)
		if (completion_done(&vmbus_connection.unload_event))
		goto completed;

		for_each_online_cpu(cpu) {
		for_each_present_cpu(cpu) {
		struct hv_per_cpu_context *hv_cpu
		= per_cpu_ptr(hv_context.cpu_context, cpu);

		/*
		* In a CoCo VM the synic_message_page is not allocated
		* in hv_synic_alloc(). Instead it is set/cleared in
		* hv_synic_enable_regs() and hv_synic_disable_regs()
		* such that it is set only when the CPU is online. If
		* not all present CPUs are online, the message page
		* might be NULL, so skip such CPUs.
		*/
		page_addr = hv_cpu->synic_message_page;
		if (!page_addr)
		continue;

		msg = (struct hv_message *)page_addr
		+ VMBUS_MESSAGE_SINT;

		@@ -840,11 +851,14 @@ static void vmbus_wait_for_unload(void)
		* maybe-pending messages on all CPUs to be able to receive new
		* messages after we reconnect.
		*/
		for_each_online_cpu(cpu) {
		for_each_present_cpu(cpu) {
		struct hv_per_cpu_context *hv_cpu
		= per_cpu_ptr(hv_context.cpu_context, cpu);

		page_addr = hv_cpu->synic_message_page;
		if (!page_addr)
		continue;

		msg = (struct hv_message *)page_addr + VMBUS_MESSAGE_SINT;
		msg->header.message_type = HVMSG_NONE;
		}