[PATCH] xen/arm: psci: Do not keep a rejected PSCI version in psci_ver

[Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>]

psci_init_0_2() stores the value returned by PSCI_VERSION in the global
psci_ver before checking that Xen supports it. When the firmware reports
a version other than 0.2 or 1.x, the function prints "Unrecognized PSCI
version" and returns -EOPNOTSUPP, but psci_ver keeps the rejected value
and psci_cpu_on_nr stays 0.

psci_init() then tries the PSCI 0.1 fallback, which overwrites psci_ver
on success. When the fallback fails as well (the /psci node is not
compatible with "arm,psci", it has no "cpu_on" property, or Xen boots
with ACPI), psci_init() returns an error that smp_init_cpus() ignores,
and psci_ver still holds the rejected version. All the users of
psci_ver then consider PSCI as available:
 - on arm64, smp_psci_init() installs call_psci_cpu_on() as the method
   to bring up the secondary CPUs;
 - on arm32, platform_cpu_up() calls call_psci_cpu_on() instead of the
   platform specific cpu_up() callback;
 - call_psci_cpu_off(), call_psci_system_off() and
   call_psci_system_reset() issue their PSCI calls.

As a result, Xen brings up each secondary CPU with an SMC using function
ID 0. An SMCCC compliant firmware refuses it, and Xen reports "Failed to
bring up CPU<n> (error -1)" for each secondary CPU.

Only set psci_ver once the version has been accepted, so that a rejected
version leaves psci_ver at 0 and Xen behaves as if PSCI was not
available. In the case above, Xen no longer issues any other PSCI call:
on arm64 the secondary CPUs using the "psci" enable-method are rejected
by smp_psci_init() and Xen boots on the boot CPU only; on arm32
platform_cpu_up() uses the platform cpu_up() callback, if any. CPU_OFF,
SYSTEM_OFF and SYSTEM_RESET are not issued either, as when the PSCI 0.1
fallback is used.

Fixes: 4d3d72c01467 ("xen/arm: Initial support for PSCI-0.2")
Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
---
 xen/arch/arm/psci.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/xen/arch/arm/psci.c b/xen/arch/arm/psci.c
index 634d0d7467..a720cf8d41 100644
--- a/xen/arch/arm/psci.c
+++ b/xen/arch/arm/psci.c
@@ -169,6 +169,7 @@ static int __init psci_init_0_2(void)
     };
     int ret;
     struct arm_smccc_res res;
+    uint32_t ver;
 
     if ( acpi_disabled )
     {
@@ -191,16 +192,17 @@ static int __init psci_init_0_2(void)
     }
 
     res = arm_smccc_smc(PSCI_0_2_FN32_PSCI_VERSION);
-    psci_ver = PSCI_RET(res);
+    ver = PSCI_RET(res);
 
     /* For the moment, we only support PSCI 0.2 and PSCI 1.x */
-    if ( psci_ver != PSCI_VERSION(0, 2) && PSCI_VERSION_MAJOR(psci_ver) != 1 )
+    if ( ver != PSCI_VERSION(0, 2) && PSCI_VERSION_MAJOR(ver) != 1 )
     {
         printk("Error: Unrecognized PSCI version %u.%u\n",
-               PSCI_VERSION_MAJOR(psci_ver), PSCI_VERSION_MINOR(psci_ver));
+               PSCI_VERSION_MAJOR(ver), PSCI_VERSION_MINOR(ver));
         return -EOPNOTSUPP;
     }
 
+    psci_ver = ver;
     psci_cpu_on_nr = PSCI_0_2_FN_NATIVE(CPU_ON);
 
     return 0;
-- 
2.25.1