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Re: [Xen-devel] [PATCH 05/18] xen/arm: Trigger Xen suspend when Dom0 completes suspend


On 11/12/18 11:30 AM, Mirela Simonovic wrote:
When Dom0 finalizes its suspend procedure the suspend of Xen is
triggered by calling system_suspend(). Dom0 finalizes the suspend from
its boot core (VCPU#0), which could be mapped to any physical CPU,
i.e. the system_suspend() function could be executed by any physical
CPU. Since Xen suspend procedure has to be run by the boot CPU
(non-boot CPUs will be disabled at some point in suspend procedure),
system_suspend() execution has to continue on CPU#0.

Nothing in the domain_suspend code checks that domain_suspend is called by vCPU0. I also can't find any restriction in the PSCI spec to run on pCPU0. Can you provide more details why this required?

When the system_suspend() returns 0, it means that the system was
suspended and it is coming out of the resume procedure. Regardless
of the system_suspend() return value, after this function returns
Xen is fully functional, and its state, including all devices and data
structures, matches the state prior to calling system_suspend().
The status is returned by system_suspend() for debugging/logging
purposes and function prototype compatibility.

Signed-off-by: Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>
Signed-off-by: Saeed Nowshadi <saeed.nowshadi@xxxxxxxxxx>
  xen/arch/arm/suspend.c | 34 ++++++++++++++++++++++++++++++++++
  1 file changed, 34 insertions(+)

diff --git a/xen/arch/arm/suspend.c b/xen/arch/arm/suspend.c
index f2338e41db..21b45f8248 100644
--- a/xen/arch/arm/suspend.c
+++ b/xen/arch/arm/suspend.c
@@ -112,11 +112,20 @@ static void vcpu_suspend(register_t epoint, register_t 
      _arch_set_info_guest(v, &ctxt);
+/* Xen suspend. Note: data is not used (suspend is the suspend to RAM) */
+static long system_suspend(void *data)
+    BUG_ON(system_state != SYS_STATE_active);
+    return -ENOSYS;
  int32_t domain_suspend(register_t epoint, register_t cid)
      struct vcpu *v;
      struct domain *d = current->domain;
      bool is_thumb = epoint & 1;
+    int status;
              "Dom%d suspend: epoint=0x%"PRIregister", cid=0x%"PRIregister"\n",
@@ -156,6 +165,31 @@ int32_t domain_suspend(register_t epoint, register_t cid)
+ /* If this was dom0 the whole system should suspend: trigger Xen suspend */
+    if ( is_hardware_domain(d) )
+    {
+        /*
+         * system_suspend should be called when Dom0 finalizes the suspend
+         * procedure from its boot core (VCPU#0). However, Dom0's VCPU#0 could
+         * be mapped to any PCPU (this function could be executed by any PCPU).
+         * The suspend procedure has to be finalized by the PCPU#0 (non-boot
+         * PCPUs will be disabled during the suspend).
+         */
+        status = continue_hypercall_on_cpu(0, system_suspend, NULL);
+        /*
+         * If an error happened, there is nothing that needs to be done here
+         * because the system_suspend always returns in fully functional state
+         * no matter what the outcome of suspend procedure is. If the system
+         * suspended successfully the function will return 0 after the resume.
+         * Otherwise, if an error is returned it means Xen did not suspended,
+         * but it is still in the same state as if the system_suspend was never
+         * called. We dump a debug message in case of an error for debugging/
+         * logging purpose.
+         */
+        if ( status )
+            dprintk(XENLOG_ERR, "Failed to suspend, errno=%d\n", status);
+    }
      return PSCI_SUCCESS;

Julien Grall

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