arm/vm_event: get/set registers

Add support for getting/setting registers through vm_event on ARM. Only
TTB/CR/R0/R1, PC and CPSR are sent as part of a request and only PC is set
as part of a response. The set of registers can be expanded in the future to
include other registers as well if necessary.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@zentific.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

xen/arch/arm/Makefile

@@ -43,6 +43,7 @@ obj-y += traps.o
 obj-y += vgic.o
 obj-y += vgic-v2.o
 obj-$(CONFIG_ARM_64) += vgic-v3.o
+obj-y += vm_event.o
 obj-y += vtimer.o
 obj-y += vpsci.o
 obj-y += vuart.o

xen/arch/arm/vm_event.c

@@ -0,0 +1,52 @@
+/*
+ * arch/arm/vm_event.c
+ *
+ * Architecture-specific vm_event handling routines
+ *
+ * Copyright (c) 2016 Tamas K Lengyel (tamas.lengyel@zentific.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <xen/sched.h>
+#include <asm/vm_event.h>
+
+void vm_event_fill_regs(vm_event_request_t *req)
+{
+    const struct cpu_user_regs *regs = guest_cpu_user_regs();
+
+    req->data.regs.arm.cpsr = regs->cpsr;
+    req->data.regs.arm.pc = regs->pc;
+    req->data.regs.arm.ttbcr = READ_SYSREG(TCR_EL1);
+    req->data.regs.arm.ttbr0 = READ_SYSREG64(TTBR0_EL1);
+    req->data.regs.arm.ttbr1 = READ_SYSREG64(TTBR1_EL1);
+}
+
+void vm_event_set_registers(struct vcpu *v, vm_event_response_t *rsp)
+{
+    struct cpu_user_regs *regs = &v->arch.cpu_info->guest_cpu_user_regs;
+
+    /* vCPU should be paused */
+    ASSERT(atomic_read(&v->vm_event_pause_count));
+
+    regs->pc = rsp->data.regs.arm.pc;
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */

xen/include/asm-arm/vm_event.h

@@ -45,15 +45,4 @@ void vm_event_register_write_resume(struct vcpu *v, vm_event_response_t *rsp)
     /* Not supported on ARM. */
 }
 
-static inline
-void vm_event_set_registers(struct vcpu *v, vm_event_response_t *rsp)
-{
-    /* Not supported on ARM. */
-}
-
-static inline void vm_event_fill_regs(vm_event_request_t *req)
-{
-    /* Not supported on ARM. */
-}
-
 #endif /* __ASM_ARM_VM_EVENT_H__ */

xen/include/asm-x86/vm_event.h

@@ -39,8 +39,4 @@ void vm_event_toggle_singlestep(struct domain *d, struct vcpu *v);
 
 void vm_event_register_write_resume(struct vcpu *v, vm_event_response_t *rsp);
 
-void vm_event_set_registers(struct vcpu *v, vm_event_response_t *rsp);
-
-void vm_event_fill_regs(vm_event_request_t *req);
-
 #endif /* __ASM_X86_VM_EVENT_H__ */

xen/include/public/vm_event.h

@@ -132,8 +132,8 @@
 #define VM_EVENT_X86_XCR0   3
 
 /*
- * Using a custom struct (not hvm_hw_cpu) so as to not fill
- * the vm_event ring buffer too quickly.
+ * Using custom vCPU structs (i.e. not hvm_hw_cpu) for both x86 and ARM
+ * so as to not fill the vm_event ring buffer too quickly.
  */
 struct vm_event_regs_x86 {
     uint64_t rax;
@@ -171,6 +171,19 @@ struct vm_event_regs_x86 {
     uint32_t _pad;
 };
 
+/*
+ * Only the register 'pc' can be set on a vm_event response using the
+ * VM_EVENT_FLAG_SET_REGISTERS flag.
+ */
+struct vm_event_regs_arm {
+    uint64_t ttbr0;
+    uint64_t ttbr1;
+    uint64_t ttbcr;
+    uint64_t pc;
+    uint32_t cpsr;
+    uint32_t _pad;
+};
+
 /*
  * mem_access flag definitions
  *
@@ -275,6 +288,7 @@ typedef struct vm_event_st {
     union {
         union {
             struct vm_event_regs_x86 x86;
+            struct vm_event_regs_arm arm;
         } regs;
 
         struct vm_event_emul_read_data emul_read_data;

xen/include/xen/vm_event.h

@@ -75,6 +75,9 @@ int vm_event_domctl(struct domain *d, xen_domctl_vm_event_op_t *vec,
 void vm_event_vcpu_pause(struct vcpu *v);
 void vm_event_vcpu_unpause(struct vcpu *v);
 
+void vm_event_fill_regs(vm_event_request_t *req);
+void vm_event_set_registers(struct vcpu *v, vm_event_response_t *rsp);
+
 #endif /* __VM_EVENT_H__ */
 
 /*