[PATCH v4][PART 2 09/10] xen/arm: Resume memory management on Xen resume

[Mykola Kvach <xakep.amatop@xxxxxxxxx>]

From: Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>

The MMU must be enabled during the resume path before restoring context,
as virtual addresses are used to access the saved context data.

This patch adds MMU setup during resume by reusing the existing
enable_secondary_cpu_mm function, which enables data cache and the MMU.
Before the MMU is enabled, the content of TTBR0_EL2 is changed to point
to init_ttbr (page tables used at runtime).

On boot, init_ttbr is normally initialized during secondary CPU hotplug.
On uniprocessor systems, this would leave init_ttbr uninitialized,
causing resume to fail. To address this, the boot CPU now sets init_ttbr
during suspend.

Signed-off-by: Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>
Signed-off-by: Saeed Nowshadi <saeed.nowshadi@xxxxxxxxxx>
Signed-off-by: Mykyta Poturai <mykyta_poturai@xxxxxxxx>
Signed-off-by: Mykola Kvach <mykola_kvach@xxxxxxxx>
---
Changes in v4:
- Drop unnecessary DAIF masking; interrupts are already masked on resume
- Remove leftover TLB flush instructions; flushing is done in enable_mmu
- Avoid setting x19 in hyp_resume; not needed
- Replace prepare_secondary_mm with set_init_ttbr; call it from system_suspend

Changes in v3:
- Update commit message for clarity
- Replace create_page_tables, enable_mmu, and mmu_init_secondary_cpu
  with enable_secondary_cpu_mm
- Move prepare_secondary_mm to start_xen to avoid crash
- Add early UART init during resume

Changes in v2:
- Move hyp_resume to head.S to keep resume logic together
- Simplify hyp_resume using existing helpers: check_cpu_mode, cpu_init,
  create_page_tables, enable_mmu
---
 xen/arch/arm/arm64/head.S     | 16 ++++++++++++++++
 xen/arch/arm/include/asm/mm.h |  2 ++
 xen/arch/arm/mmu/smpboot.c    |  2 +-
 xen/arch/arm/suspend.c        |  2 ++
 4 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 3522c497c5..596e960152 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -564,6 +564,22 @@ END(efi_xen_start)
 #ifdef CONFIG_SYSTEM_SUSPEND
 
 FUNC(hyp_resume)
+        /* 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   x0, =start
+        adr   x20, start             /* x20 := paddr (start) */
+        sub   x20, x20, x0           /* x20 := phys-offset */
+        ldr   lr, =mmu_resumed
+        b     enable_secondary_cpu_mm
+
+mmu_resumed:
         b .
 END(hyp_resume)
 
diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
index 011bc1fd30..868282ec06 100644
--- a/xen/arch/arm/include/asm/mm.h
+++ b/xen/arch/arm/include/asm/mm.h
@@ -363,6 +363,8 @@ static inline void page_set_xenheap_gfn(struct page_info 
*p, gfn_t gfn)
     } while ( (y = cmpxchg(&p->u.inuse.type_info, x, nx)) != x );
 }
 
+void set_init_ttbr(lpae_t *root);
+
 #endif /*  __ARCH_ARM_MM__ */
 /*
  * Local variables:
diff --git a/xen/arch/arm/mmu/smpboot.c b/xen/arch/arm/mmu/smpboot.c
index 37e91d72b7..ff508ecf40 100644
--- a/xen/arch/arm/mmu/smpboot.c
+++ b/xen/arch/arm/mmu/smpboot.c
@@ -72,7 +72,7 @@ static void clear_boot_pagetables(void)
     clear_table(boot_third);
 }
 
-static void set_init_ttbr(lpae_t *root)
+void set_init_ttbr(lpae_t *root)
 {
     /*
      * init_ttbr is part of the identity mapping which is read-only. So
diff --git a/xen/arch/arm/suspend.c b/xen/arch/arm/suspend.c
index e3a9b68622..f3ad8517ac 100644
--- a/xen/arch/arm/suspend.c
+++ b/xen/arch/arm/suspend.c
@@ -65,6 +65,8 @@ static long system_suspend(void *data)
         goto resume_console;
     }
 
+    set_init_ttbr(xen_pgtable);
+
     /*
      * Enable identity mapping before entering suspend to simplify
      * the resume path
-- 
2.48.1