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[Xen-devel] [PATCH v2 05/10] xen/arm: Setup virtual paging for non-boot CPUs on hotplug/resume

In existing code the paging for non-boot CPUs is setup only on boot. The
setup is triggered from start_xen() after all CPUs are brought online.
In other words, the initialization of VTCR_EL2 register is done out of the
cpu_up/start_secondary() control flow. However, the cpu_up flow is also used
to hotplug non-boot CPUs on resume from suspend to RAM state, in which case
the virtual paging will not be configured.
With this patch the setting of paging is triggered from start_secondary()
function if the current system state is not boot. This way, the paging
for secondary CPUs will be setup in non-boot scenarios as well, while the
setup in boot scenario remains unchanged.
It is assumed here that after the system completed the boot, CPUs that
execute start_secondary() were booted as well when the Xen itself was
booted. According to this assumption non-boot CPUs will always be compliant
with the VTCR_EL2 value that was selected by Xen on boot.
Currently, these in no mechanism to trigger hotplugging of a CPU. This
will be added with the suspend to RAM support for ARM, where the hotplug
of non-boot CPUs will be triggered via enable_nonboot_cpus() call.

Signed-off-by: Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>

CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
Changes in v2:
-Fix commit message
-Save configured VTCR_EL2 value into static variable that will be used
 by non-boot CPUs on hotplug
-Add setup_virt_paging_secondary() and invoke it from start_secondary()
 if that CPU has to setup virtual paging (if the system state is not boot)
 xen/arch/arm/p2m.c        | 13 ++++++++++++-
 xen/arch/arm/smpboot.c    |  3 +++
 xen/include/asm-arm/p2m.h |  3 +++
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index d43c3aa896..9bb62c13cd 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -1451,13 +1451,21 @@ err:
     return page;
-static void __init setup_virt_paging_one(void *data)
+static void setup_virt_paging_one(void *data)
     unsigned long val = (unsigned long)data;
     WRITE_SYSREG32(val, VTCR_EL2);
+/* VTCR value to be configured by all CPUs. Set only once by the boot CPU */
+static unsigned long __read_mostly vtcr_value;
+void setup_virt_paging_secondary(void)
+    setup_virt_paging_one((void *)vtcr_value);
 void __init setup_virt_paging(void)
     /* Setup Stage 2 address translation */
@@ -1540,6 +1548,9 @@ void __init setup_virt_paging(void)
     BUG_ON( P2M_ROOT_LEVEL == 0 && P2M_ROOT_ORDER > 0 );
     setup_virt_paging_one((void *)val);
     smp_call_function(setup_virt_paging_one, (void *)val, 1);
+    /* Save configured value (to be used later for secondary CPUs hotplug) */
+    vtcr_value = val;
diff --git a/xen/arch/arm/smpboot.c b/xen/arch/arm/smpboot.c
index 38b665a6d2..abc642804f 100644
--- a/xen/arch/arm/smpboot.c
+++ b/xen/arch/arm/smpboot.c
@@ -358,6 +358,9 @@ void start_secondary(unsigned long boot_phys_offset,
+    if ( system_state != SYS_STATE_boot )
+        setup_virt_paging_secondary();
     printk(XENLOG_DEBUG "CPU %u booted.\n", smp_processor_id());
diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
index 8823707c17..85b66a1196 100644
--- a/xen/include/asm-arm/p2m.h
+++ b/xen/include/asm-arm/p2m.h
@@ -153,6 +153,9 @@ void p2m_altp2m_check(struct vcpu *v, uint16_t idx)
 /* Second stage paging setup, to be called on all CPUs */
 void setup_virt_paging(void);
+/* To be called by secondary CPU on hotplug */
+void setup_virt_paging_secondary(void);
 /* Init the datastructures for later use by the p2m code */
 int p2m_init(struct domain *d);

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