Hi Mykola,
On 27/05/2025 10:18, Mykola Kvach wrote:
From: Mykola Kvach <mykola_kv...@epam.com>
This patch adds support for the PSCI SYSTEM_SUSPEND function in the vPSCI
(virtual PSCI) interface, allowing guests to request suspend via the PSCI
v1.0 SYSTEM_SUSPEND call (both 32-bit and 64-bit variants).
The implementation:
- Adds SYSTEM_SUSPEND function IDs to PSCI definitions
- Implements trapping and handling of SYSTEM_SUSPEND in vPSCI
- Allows only non-hardware domains to invoke SYSTEM_SUSPEND; for the
hardware domain, PSCI_NOT_SUPPORTED is returned to avoid halting the
system in hwdom_shutdown() called from domain_shutdown
- Ensures all secondary VCPUs of the calling domain are offline before
allowing suspend due to PSCI spec
- Treats suspend as a "standby" operation: the domain is shut down with
SHUTDOWN_suspend, and resumes execution at the instruction following
the call
Looking at the specification, I am still not convinced you can implement
PSCI SUSPEND as a NOP. For instance, in the section "5.1.19
SYSTEM_SUSPEND", the wording implies the call cannot return when it is
successul.
I understand that 5.20.2 ("Caller reponsabilities" for SYSTEM_SUSPEND)
suggests the caller should apply all the rules from 5.4 ("Caller
responsabilties" for CPU_SUSPEND), but it is also mentioned that
SYSTEM_SUSPEND behave as the deepest power down state.
So I don't think standby is an option. I would like an opinion from the
other maintainers.
+static int32_t do_psci_1_0_system_suspend(register_t epoint, register_t cid)
> +{> + struct vcpu *v;
+ struct domain *d = current->domain;
+
+ /* Drop this check once SYSTEM_SUSPEND is supported in hardware domain */
+ if ( is_hardware_domain(d) )
+ return PSCI_NOT_SUPPORTED;
+
+ /* Ensure that all CPUs other than the calling one are offline */
+ for_each_vcpu ( d, v )
+ {
+ if ( v != current && is_vcpu_online(v) )
I think this is racy because you can still turn on a vCPU afterwards
from a vCPU you haven't checked.
Did you add this check just to follow the specification, or is there any
other problem in Xen?
+ return PSCI_DENIED;
> + }> +
+ /*
+ * System suspend requests are treated as performing standby
+ * as this simplifies Xen implementation.
+ *
+ * Arm Power State Coordination Interface (DEN0022F.b)
This comment is a bit too verbose. There is no need to copy/paste the
specification. You can just write a couple of sentence with link to the
specification.
Cheers,
--
Julien Grall
