resume: Don't attempt to use generic reboot mechanisms on QEMU

On QEMU it's necessary to manually reset the BIOS memory region
between 0xc0000-0x100000 on a reboot.  After this manual memory reset
is completed, it's not valid to use the generic reset mechanisms.
Rename qemu_prep_reset() to qemu_reboot() and change the function to
immediately reboot after the code memcpy.

This fixes a bug that could cause code corruption on reboots - calling
the udelay() function (as invoked by i8042_reboot and/or pci_reboot)
was not valid after the BIOS was memcpy'd.

Reported-by: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Tested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/fw/shadow.c

@@ -167,7 +167,7 @@ make_bios_readonly(void)
 }
 
 void
-qemu_prep_reset(void)
+qemu_reboot(void)
 {
     if (!CONFIG_QEMU || runningOnXen())
         return;
@@ -187,4 +187,16 @@ qemu_prep_reset(void)
     memcpy(hrp + 4, hrp + 4 + BIOS_SRC_OFFSET, cend - (hrp + 4));
     barrier();
     HaveRunPost = 0;
+    barrier();
+
+    // Request a QEMU system reset.  Do the reset in this function as
+    // the BIOS code was overwritten above and not all BIOS
+    // functionality may be available.
+
+    // Attempt PCI style reset
+    outb(0x02, PORT_PCI_REBOOT);
+    outb(0x06, PORT_PCI_REBOOT);
+
+    // Next try triple faulting the CPU to force a reset
+    asm volatile("int3");
 }

src/hw/pci.c

@@ -12,7 +12,6 @@
 #include "x86.h" // outl
 
 #define PORT_PCI_CMD           0x0cf8
-#define PORT_PCI_REBOOT        0x0cf9
 #define PORT_PCI_DATA          0x0cfc
 
 void pci_config_writel(u16 bdf, u32 addr, u32 val)

src/hw/pci.h

@@ -3,6 +3,8 @@
 
 #include "types.h" // u32
 
+#define PORT_PCI_REBOOT        0x0cf9
+
 static inline u8 pci_bdf_to_bus(u16 bdf) {
     return bdf >> 8;
 }

src/resume.c

@@ -125,8 +125,8 @@ tryReboot(void)
 {
     dprintf(1, "Attempting a hard reboot\n");
 
-    // Setup for reset on qemu.
-    qemu_prep_reset();
+    // Use a QEMU specific reboot on QEMU
+    qemu_reboot();
 
     // Reboot using ACPI RESET_REG
     acpi_reboot();

src/util.h

@@ -123,7 +123,7 @@ void pirtable_setup(void);
 // fw/shadow.c
 void make_bios_writable(void);
 void make_bios_readonly(void);
-void qemu_prep_reset(void);
+void qemu_reboot(void);
 
 // fw/smbios.c
 void smbios_legacy_setup(void);