From a3440f2b485d00e10fcb952181305ffe62783416 Mon Sep 17 00:00:00 2001
From: Hector Martin <marcan@marcan.st>
Date: Wed, 5 May 2021 00:24:52 +0900
Subject: [PATCH] hv: Support cleanly exiting the hypervisor from an exception

Signed-off-by: Hector Martin <marcan@marcan.st>
---
 proxyclient/hv.py    | 13 ++++++++-----
 proxyclient/proxy.py |  2 +-
 src/hv.c             |  4 +++-
 src/hv_asm.S         | 31 +++++++++++++++++++++++++++++--
 src/hv_exc.c         | 31 ++++++++++++++++++++-----------
 src/uartproxy.h      |  1 +
 6 files changed, 62 insertions(+), 20 deletions(-)

diff --git a/proxyclient/hv.py b/proxyclient/hv.py
index b1a3ced4..67522dd2 100644
--- a/proxyclient/hv.py
+++ b/proxyclient/hv.py
@@ -54,20 +54,23 @@ class HV:
         for attr in dir(self):
             locals[attr] = getattr(self, attr)
 
-        shell.run_shell(locals, "Entering debug shell", "Returning from exception")
+        ret = shell.run_shell(locals, "Entering debug shell", "Returning from exception")
+
+        if ret is None:
+            ret = EXC_RET.HANDLED
 
         self.iface.writemem(info, ExcInfo.build(self.ctx))
-        self.p.exit(EXC_RET.HANDLED)
+        self.p.exit(ret)
 
     def skip(self):
         self.ctx.elr += 4
-        raise shell.ExitConsole()
+        raise shell.ExitConsole(EXC_RET.HANDLED)
 
     def cont(self):
-        raise shell.ExitConsole()
+        raise shell.ExitConsole(EXC_RET.HANDLED)
 
     def exit(self):
-        sys.exit(0)
+        raise shell.ExitConsole(EXC_RET.EXIT_GUEST)
 
     def init(self):
         self.adt = load_adt(self.u.get_adt())
diff --git a/proxyclient/proxy.py b/proxyclient/proxy.py
index 36fb0468..e0d2dc0f 100755
--- a/proxyclient/proxy.py
+++ b/proxyclient/proxy.py
@@ -90,6 +90,7 @@ class EXC(IntEnum):
 class EXC_RET(IntEnum):
     UNHANDLED = 1
     HANDLED = 2
+    EXIT_GUEST = 3
 
 ExcInfo = Struct(
     "spsr" / RegAdapter(SPSR),
@@ -802,7 +803,6 @@ class M1N1Proxy:
     def hv_map(self, from_, to, size, incr):
         return self.request(self.P_HV_MAP, from_, to, size, incr)
     def hv_start(self, entry, *args):
-        # does not return
         return self.request(self.P_HV_START, entry, *args)
 
 if __name__ == "__main__":
diff --git a/src/hv.c b/src/hv.c
index 6f4d13a7..9adff2fa 100644
--- a/src/hv.c
+++ b/src/hv.c
@@ -4,7 +4,7 @@
 #include "assert.h"
 #include "cpu_regs.h"
 
-void hv_enter_guest(u64 x0, u64 x1, u64 x2, u64 x3, void *entry) __attribute__((noreturn));
+void hv_enter_guest(u64 x0, u64 x1, u64 x2, u64 x3, void *entry);
 
 extern char _hv_vectors_start[0];
 
@@ -38,4 +38,6 @@ void hv_start(void *entry, u64 regs[4])
     msr(VBAR_EL1, _hv_vectors_start);
 
     hv_enter_guest(regs[0], regs[1], regs[2], regs[3], entry);
+
+    printf("Exiting hypervisor.\n");
 }
diff --git a/src/hv_asm.S b/src/hv_asm.S
index ccbea3d5..f92f7bbc 100644
--- a/src/hv_asm.S
+++ b/src/hv_asm.S
@@ -84,6 +84,17 @@ _v_hv_serr:
 .globl hv_enter_guest
 .type hv_enter_guest, @function
 hv_enter_guest:
+    stp x29, x30, [sp, #-16]!
+    stp x27, x28, [sp, #-16]!
+    stp x25, x26, [sp, #-16]!
+    stp x23, x24, [sp, #-16]!
+    stp x21, x22, [sp, #-16]!
+    stp x19, x20, [sp, #-16]!
+    str x18, [sp, #-16]!
+
+    mov x5, sp
+    msr tpidr_el2, x5
+
     mrs x5, daif
     msr daifclr, 3
     mov x6, #5
@@ -91,8 +102,24 @@ hv_enter_guest:
     msr spsr_el2, x5
 
     msr elr_el2, x4
-    msr spsel, #0
     mov x5, #0
-    mov sp, x5
+    msr sp_el0, x5
+    msr sp_el1, x5
 
     eret
+
+.globl hv_exit_guest
+.type hv_exit_guest, @function
+hv_exit_guest:
+    mrs x5, tpidr_el2
+    mov sp, x5
+
+    ldr x18, [sp], #16
+    ldp x19, x20, [sp], #16
+    ldp x21, x22, [sp], #16
+    ldp x23, x24, [sp], #16
+    ldp x25, x26, [sp], #16
+    ldp x27, x28, [sp], #16
+    ldp x29, x30, [sp], #16
+
+    ret
diff --git a/src/hv_exc.c b/src/hv_exc.c
index 9cc425e1..491fe878 100644
--- a/src/hv_exc.c
+++ b/src/hv_exc.c
@@ -7,6 +7,8 @@
 #include "string.h"
 #include "uartproxy.h"
 
+void hv_exit_guest(void) __attribute__((noreturn));
+
 static void hv_exc_proxy(u64 *regs, uartproxy_exc_code_t type)
 {
     struct uartproxy_exc_info exc_info = {
@@ -27,18 +29,25 @@ static void hv_exc_proxy(u64 *regs, uartproxy_exc_code_t type)
 
     int ret = uartproxy_run(&start);
 
-    if (ret == EXC_RET_HANDLED) {
-        memcpy(regs, exc_info.regs, sizeof(exc_info.regs));
-        msr(SPSR_EL2, exc_info.spsr);
-        msr(ELR_EL2, exc_info.elr);
-        msr(SP_EL0, exc_info.sp[0]);
-        msr(SP_EL1, exc_info.sp[1]);
-        return;
+    switch (ret) {
+        case EXC_RET_HANDLED:
+            memcpy(regs, exc_info.regs, sizeof(exc_info.regs));
+            msr(SPSR_EL2, exc_info.spsr);
+            msr(ELR_EL2, exc_info.elr);
+            msr(SP_EL0, exc_info.sp[0]);
+            msr(SP_EL1, exc_info.sp[1]);
+            return;
+        case EXC_EXIT_GUEST:
+            hv_exit_guest();
+        default:
+            printf("Guest exception not handled, rebooting.\n");
+            print_regs(regs, 0);
+            for (int i = 0; i < 300; i++) {
+                iodev_console_kick();
+                udelay(1000);
+            }
+            reboot();
     }
-
-    printf("Guest exception not handled, rebooting.\n");
-    print_regs(regs, 0);
-    reboot();
 }
 
 void hv_exc_sync(u64 *regs)
diff --git a/src/uartproxy.h b/src/uartproxy.h
index e46643a1..6887087a 100644
--- a/src/uartproxy.h
+++ b/src/uartproxy.h
@@ -23,6 +23,7 @@ typedef enum _uartproxy_exc_code_t {
 typedef enum _uartproxy_exc_ret_t {
     EXC_RET_UNHANDLED = 1,
     EXC_RET_HANDLED = 2,
+    EXC_EXIT_GUEST = 3,
 } uartproxy_exc_ret_t;
 
 struct uartproxy_exc_info {