[Xen-devel] [PATCH v4 19/19] xen/arm: vpsci: Rework the logic to start AArch32 vCPU in Thumb mode

[Julien Grall <julien.grall@xxxxxxx>]

32-bit domain is able to select the instruction (ARM vs Thumb) to use
when boot a new vCPU via CPU_ON. This is indicated via bit[0] of the
entry point address (see "T32 support" in PSCI v1.1 DEN0022D). bit[0]
must be cleared when setting the PC.

At the moment, Xen is setting the CPSR.T but never clear bit[0]. Clear
it to match the specification.

At the same time, slighlty rework the code to make clear thumb is only for
32-bit domain. Lastly, take the opportunity to switch is_thumb from int
to bool.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>

---
    Changes in v4:
        - Add Stefano's reviewed-by
        - Add Andre's reviewed-by

    Changes in v3:
        - Patch added
---
 xen/arch/arm/vpsci.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/xen/arch/arm/vpsci.c b/xen/arch/arm/vpsci.c
index 1729f7071e..9f4e5b8844 100644
--- a/xen/arch/arm/vpsci.c
+++ b/xen/arch/arm/vpsci.c
@@ -28,7 +28,7 @@ static int do_common_cpu_on(register_t target_cpu, register_t 
entry_point,
     struct domain *d = current->domain;
     struct vcpu_guest_context *ctxt;
     int rc;
-    int is_thumb = entry_point & 1;
+    bool is_thumb = entry_point & 1;
     register_t vcpuid;
 
     vcpuid = vaffinity_to_vcpuid(target_cpu);
@@ -62,6 +62,13 @@ static int do_common_cpu_on(register_t target_cpu, 
register_t entry_point,
     if ( is_32bit_domain(d) )
     {
         ctxt->user_regs.cpsr = PSR_GUEST32_INIT;
+        /* Start the VCPU with THUMB set if it's requested by the kernel */
+        if ( is_thumb )
+        {
+            ctxt->user_regs.cpsr |= PSR_THUMB;
+            ctxt->user_regs.pc64 &= ~(u64)1;
+        }
+
         ctxt->user_regs.r0_usr = context_id;
     }
 #ifdef CONFIG_ARM_64
@@ -71,10 +78,6 @@ static int do_common_cpu_on(register_t target_cpu, 
register_t entry_point,
         ctxt->user_regs.x0 = context_id;
     }
 #endif
-
-    /* Start the VCPU with THUMB set if it's requested by the kernel */
-    if ( is_thumb )
-        ctxt->user_regs.cpsr |= PSR_THUMB;
     ctxt->flags = VGCF_online;
 
     domain_lock(d);
-- 
2.11.0


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