resume: Make KVM soft reboot loop detection more flexible

Move the check for soft reboot loops from resume.c to shadow.c and
directly check for the case where the copy of the BIOS in flash
appears to be a memory alias instead.  This prevents a hang if an
external reboot request occurs during the BIOS memcpy.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

2 files changed, 13 insertions, 11 deletions

diff --git a/src/fw/shadow.c b/src/fw/shadow.c
index ee87d36..4486884 100644
--- a/src/fw/shadow.c
+++ b/src/fw/shadow.c
@@ -163,7 +163,18 @@ qemu_prep_reset(void)
         return;
     // QEMU doesn't map 0xc0000-0xfffff back to the original rom on a
     // reset, so do that manually before invoking a hard reset.
+    void *cstart = VSYMBOL(code32flat_start), *cend = VSYMBOL(code32flat_end);
+    void *hrp = &HaveRunPost;
+    if (readl(hrp + BIOS_SRC_OFFSET)) {
+        // Some old versions of KVM don't store a pristine copy of the
+        // BIOS in high memory.  Try to shutdown the machine instead.
+        dprintf(1, "Unable to hard-reboot machine - attempting shutdown.\n");
+        apm_shutdown();
+    }
+    // Copy the BIOS making sure to only reset HaveRunPost at end
     make_bios_writable();
-    memcpy(VSYMBOL(code32flat_start), VSYMBOL(code32flat_start) + BIOS_SRC_OFFSET
-           , SYMBOL(code32flat_end) - SYMBOL(code32flat_start));
+    memcpy(cstart, cstart + BIOS_SRC_OFFSET, hrp - cstart);
+    memcpy(hrp + 4, hrp + 4 + BIOS_SRC_OFFSET, cend - (hrp + 4));
+    barrier();
+    HaveRunPost = 0;
 }
diff --git a/src/resume.c b/src/resume.c
index a5465d8..afeadcf 100644
--- a/src/resume.c
+++ b/src/resume.c
@@ -114,19 +114,10 @@ s3_resume(void)
     farcall16big(&br);
 }
 
-u8 HaveAttemptedReboot VARLOW;
-
 // Attempt to invoke a hard-reboot.
 static void
 tryReboot(void)
 {
-    if (HaveAttemptedReboot) {
-        // Hard reboot has failed - try to shutdown machine.
-        dprintf(1, "Unable to hard-reboot machine - attempting shutdown.\n");
-        apm_shutdown();
-    }
-    HaveAttemptedReboot = 1;
-
     dprintf(1, "Attempting a hard reboot\n");
 
     // Setup for reset on qemu.