From: Mirela Simonovic <mirela.simonovic@aggios.com>

The MMU needs to be enabled in the resume flow before the context
can be restored (we need to be able to access the context data by
virtual address in order to restore it). The configuration of system
registers prior to branching to the routine that sets up the page
tables is copied from xen/arch/arm/arm64/head.S.
After the MMU is enabled, the content of TTBR0_EL2 is changed to
point to init_ttbr (page tables used at runtime).

At boot the init_ttbr variable is updated when a secondary CPU is
hotplugged. In the scenario where there is only one physical CPU in
the system, the init_ttbr would not be initialized for the use in
resume flow. To get the variable initialized in all scenarios in this
patch we add that the boot CPU updates init_ttbr after it sets the
page tables for runtime.

Signed-off-by: Mirela Simonovic <mirela.simonovic@aggios.com>
Signed-off-by: Saeed Nowshadi <saeed.nowshadi@xilinx.com>
Signed-off-by: Mykyta Poturai <mykyta_poturai@epam.com>
Signed-off-by: Mykola Kvach <mykola_kvach@epam.com>
---
Changes in V3:
- updated commit message
- instead of using create_page_tables, enable_mmu, and mmu_init_secondary_cpu,
  the existing function enable_secondary_cpu_mm is now used
- prepare_secondary_mm (previously init_secondary_pagetables in the previous
  patch series) is now called at the end of start_xen instead of
  setup_pagetables. Calling it in the previous location caused a crash
- add early printk init during resume

Changes in V2:
- moved hyp_resume to head.S to place it near the rest of the start code
- simplified the code in hyp_resume by using existing functions such as
  check_cpu_mode, cpu_init, create_page_tables, and enable_mmu
---
 xen/arch/arm/arm64/head.S | 23 +++++++++++++++++++++++
 xen/arch/arm/setup.c      |  8 ++++++++
 2 files changed, 31 insertions(+)

diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 3522c497c5..fab2812e54 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -564,6 +564,29 @@ END(efi_xen_start)
 #ifdef CONFIG_SYSTEM_SUSPEND
 
 FUNC(hyp_resume)
+        msr   DAIFSet, 0xf           /* Disable all interrupts */
+
+        tlbi  alle2
+        dsb   sy                     /* Ensure completion of TLB flush */
+        isb
+
+        ldr   x0, =start
+        adr   x19, start             /* x19 := paddr (start) */
+        sub   x20, x19, x0           /* x20 := phys-offset */
+
+        /* Initialize the UART if earlyprintk has been enabled. */
+#ifdef CONFIG_EARLY_PRINTK
+        bl    init_uart
+#endif
+        PRINT_ID("- Xen resuming -\r\n")
+
+        bl    check_cpu_mode
+        bl    cpu_init
+
+        ldr   lr, =mmu_resumed
+        b     enable_secondary_cpu_mm
+
+mmu_resumed:
         b .
 END(hyp_resume)
 
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index ffcae900d7..3a89ac436b 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -508,6 +508,14 @@ void asmlinkage __init start_xen(unsigned long fdt_paddr)
     for_each_domain( d )
         domain_unpause_by_systemcontroller(d);
 
+#ifdef CONFIG_SYSTEM_SUSPEND
+    /*
+     * It is called to initialize init_ttbr.
+     * Without this call, Xen gets stuck after resuming.
+     */
+    prepare_secondary_mm(0);
+#endif
+
     /* Switch on to the dynamically allocated stack for the idle vcpu
      * since the static one we're running on is about to be freed. */
     memcpy(idle_vcpu[0]->arch.cpu_info, get_cpu_info(),
-- 
2.43.0