pc-bios/s390-ccw/net: Use diag308 to reset machine before jumping to the OS

The netboot firmware so far simply jumped directly into the OS kernel
after the download has been completed. This, however, bears the risk
that the virtio-net device still might be active in the background and
incoming packets are still placed into the buffers - which could destroy
memory of the now-running Linux kernel in case it did not take over the
device fast enough. Also the SCLP console is not put into a well-defined
state here. We should hand over the system in a clean state when jumping
into the kernel, so let's use the same mechanism as it's done in the
main s390-ccw firmware and reset the machine with diag308 into a clean
state before jumping into the OS kernel code. To be able to share the
code with the main s390-ccw firmware, the related functions are now
extracted from bootmap.c into a new file called jump2ipl.c.

Since we now also set the boot device schid at address 184 for the network
boot device, this patch also slightly changes the way how we detect the
entry points for non-ELF binary images: The code now looks for the "S390EP"
magic first and then jumps to 0x10000 in case it has been found. This is
necessary for booting from network devices, since the normal kernel code
(where the PSW at ddress 0 points to) tries to do a block load from the
boot device. This of course fails for a virtio-net device and causes the
kernel to abort with a panic-PSW silently.

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

pc-bios/s390-ccw/Makefile

@@ -9,7 +9,9 @@ $(call set-vpath, $(SRC_PATH)/pc-bios/s390-ccw)
 
 .PHONY : all clean build-all
 
-OBJECTS = start.o main.o bootmap.o sclp.o virtio.o virtio-scsi.o virtio-blkdev.o libc.o menu.o
+OBJECTS = start.o main.o bootmap.o jump2ipl.o sclp.o menu.o \
+	  virtio.o virtio-scsi.o virtio-blkdev.o libc.o
+
 QEMU_CFLAGS := $(filter -W%, $(QEMU_CFLAGS))
 QEMU_CFLAGS += -ffreestanding -fno-delete-null-pointer-checks -msoft-float
 QEMU_CFLAGS += -march=z900 -fPIE -fno-strict-aliasing

pc-bios/s390-ccw/bootmap.c

@@ -29,14 +29,6 @@
 /* Scratch space */
 static uint8_t sec[MAX_SECTOR_SIZE*4] __attribute__((__aligned__(PAGE_SIZE)));
 
-typedef struct ResetInfo {
-    uint32_t ipl_mask;
-    uint32_t ipl_addr;
-    uint32_t ipl_continue;
-} ResetInfo;
-
-static ResetInfo save;
-
 const uint8_t el_torito_magic[] = "EL TORITO SPECIFICATION"
                                   "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
 
@@ -57,53 +49,6 @@ static inline bool is_iso_vd_valid(IsoVolDesc *vd)
            vd->type <= VOL_DESC_TYPE_PARTITION;
 }
 
-static void jump_to_IPL_2(void)
-{
-    ResetInfo *current = 0;
-
-    void (*ipl)(void) = (void *) (uint64_t) current->ipl_continue;
-    *current = save;
-    ipl(); /* should not return */
-}
-
-static void jump_to_IPL_code(uint64_t address)
-{
-    /* store the subsystem information _after_ the bootmap was loaded */
-    write_subsystem_identification();
-
-    /* prevent unknown IPL types in the guest */
-    if (iplb.pbt == S390_IPL_TYPE_QEMU_SCSI) {
-        iplb.pbt = S390_IPL_TYPE_CCW;
-        set_iplb(&iplb);
-    }
-
-    /*
-     * The IPL PSW is at address 0. We also must not overwrite the
-     * content of non-BIOS memory after we loaded the guest, so we
-     * save the original content and restore it in jump_to_IPL_2.
-     */
-    ResetInfo *current = 0;
-
-    save = *current;
-    current->ipl_addr = (uint32_t) (uint64_t) &jump_to_IPL_2;
-    current->ipl_continue = address & 0x7fffffff;
-
-    debug_print_int("set IPL addr to", current->ipl_continue);
-
-    /* Ensure the guest output starts fresh */
-    sclp_print("\n");
-
-    /*
-     * HACK ALERT.
-     * We use the load normal reset to keep r15 unchanged. jump_to_IPL_2
-     * can then use r15 as its stack pointer.
-     */
-    asm volatile("lghi 1,1\n\t"
-                 "diag 1,1,0x308\n\t"
-                 : : : "1", "memory");
-    panic("\n! IPL returns !\n");
-}
-
 /***********************************************************************
  * IPL an ECKD DASD (CDL or LDL/CMS format)
  */
@@ -729,13 +674,7 @@ static void load_iso_bc_entry(IsoBcSection *load)
                         (void *)((uint64_t)bswap16(s.load_segment)),
                         blks_to_load);
 
-    /* Trying to get PSW at zero address */
-    if (*((uint64_t *)0) & IPL_PSW_MASK) {
-        jump_to_IPL_code((*((uint64_t *)0)) & 0x7fffffff);
-    }
-
-    /* Try default linux start address */
-    jump_to_IPL_code(KERN_IMAGE_START);
+    jump_to_low_kernel();
 }
 
 static uint32_t find_iso_bc(void)

pc-bios/s390-ccw/bootmap.h

@@ -353,10 +353,6 @@ static inline uint32_t iso_733_to_u32(uint64_t x)
 #define ISO_SECTOR_SIZE 2048
 /* El Torito specifies boot image size in 512 byte blocks */
 #define ET_SECTOR_SHIFT 2
-#define KERN_IMAGE_START 0x010000UL
-#define PSW_MASK_64 0x0000000100000000ULL
-#define PSW_MASK_32 0x0000000080000000ULL
-#define IPL_PSW_MASK (PSW_MASK_32 | PSW_MASK_64)
 
 #define ISO_PRIMARY_VD_SECTOR 16
 

pc-bios/s390-ccw/jump2ipl.c

@@ -0,0 +1,91 @@
+/*
+ * QEMU s390-ccw firmware - jump to IPL code
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or (at
+ * your option) any later version. See the COPYING file in the top-level
+ * directory.
+ */
+
+#include "libc.h"
+#include "s390-ccw.h"
+
+#define KERN_IMAGE_START 0x010000UL
+#define PSW_MASK_64 0x0000000100000000ULL
+#define PSW_MASK_32 0x0000000080000000ULL
+#define IPL_PSW_MASK (PSW_MASK_32 | PSW_MASK_64)
+
+typedef struct ResetInfo {
+    uint32_t ipl_mask;
+    uint32_t ipl_addr;
+    uint32_t ipl_continue;
+} ResetInfo;
+
+static ResetInfo save;
+
+static void jump_to_IPL_2(void)
+{
+    ResetInfo *current = 0;
+
+    void (*ipl)(void) = (void *) (uint64_t) current->ipl_continue;
+    *current = save;
+    ipl(); /* should not return */
+}
+
+void jump_to_IPL_code(uint64_t address)
+{
+    /* store the subsystem information _after_ the bootmap was loaded */
+    write_subsystem_identification();
+
+    /* prevent unknown IPL types in the guest */
+    if (iplb.pbt == S390_IPL_TYPE_QEMU_SCSI) {
+        iplb.pbt = S390_IPL_TYPE_CCW;
+        set_iplb(&iplb);
+    }
+
+    /*
+     * The IPL PSW is at address 0. We also must not overwrite the
+     * content of non-BIOS memory after we loaded the guest, so we
+     * save the original content and restore it in jump_to_IPL_2.
+     */
+    ResetInfo *current = 0;
+
+    save = *current;
+    current->ipl_addr = (uint32_t) (uint64_t) &jump_to_IPL_2;
+    current->ipl_continue = address & 0x7fffffff;
+
+    debug_print_int("set IPL addr to", current->ipl_continue);
+
+    /* Ensure the guest output starts fresh */
+    sclp_print("\n");
+
+    /*
+     * HACK ALERT.
+     * We use the load normal reset to keep r15 unchanged. jump_to_IPL_2
+     * can then use r15 as its stack pointer.
+     */
+    asm volatile("lghi 1,1\n\t"
+                 "diag 1,1,0x308\n\t"
+                 : : : "1", "memory");
+    panic("\n! IPL returns !\n");
+}
+
+void jump_to_low_kernel(void)
+{
+    /*
+     * If it looks like a Linux binary, i.e. there is the "S390EP" magic from
+     * arch/s390/kernel/head.S here, then let's jump to the well-known Linux
+     * kernel start address (when jumping to the PSW-at-zero address instead,
+     * the kernel startup code fails when we booted from a network device).
+     */
+    if (!memcmp((char *)0x10008, "S390EP", 6)) {
+        jump_to_IPL_code(KERN_IMAGE_START);
+    }
+
+    /* Trying to get PSW at zero address */
+    if (*((uint64_t *)0) & IPL_PSW_MASK) {
+        jump_to_IPL_code((*((uint64_t *)0)) & 0x7fffffff);
+    }
+
+    /* No other option left, so use the Linux kernel start address */
+    jump_to_IPL_code(KERN_IMAGE_START);
+}

pc-bios/s390-ccw/netboot.mak

@@ -1,7 +1,8 @@
 
 SLOF_DIR := $(SRC_PATH)/roms/SLOF
 
-NETOBJS := start.o sclp.o virtio.o virtio-net.o netmain.o libnet.a libc.a
+NETOBJS := start.o sclp.o virtio.o virtio-net.o jump2ipl.o netmain.o \
+	   libnet.a libc.a
 
 LIBC_INC := -nostdinc -I$(SLOF_DIR)/lib/libc/include
 LIBNET_INC := -I$(SLOF_DIR)/lib/libnet

pc-bios/s390-ccw/netmain.c

@@ -283,6 +283,15 @@ void panic(const char *string)
     }
 }
 
+void write_subsystem_identification(void)
+{
+    SubChannelId *schid = (SubChannelId *) 184;
+    uint32_t *zeroes = (uint32_t *) 188;
+
+    *schid = net_schid;
+    *zeroes = 0;
+}
+
 static bool find_net_dev(Schib *schib, int dev_no)
 {
     int i, r;
@@ -365,7 +374,7 @@ void main(void)
 
     if (rc > 0) {
         sclp_print("Network loading done, starting kernel...\n");
-        asm volatile (" lpsw 0(%0) " : : "r"(0) : "memory");
+        jump_to_low_kernel();
     }
 
     panic("Failed to load OS from network\n");

pc-bios/s390-ccw/s390-ccw.h

@@ -87,6 +87,10 @@ ulong get_second(void);
 /* bootmap.c */
 void zipl_load(void);
 
+/* jump2ipl.c */
+void jump_to_IPL_code(uint64_t address);
+void jump_to_low_kernel(void);
+
 /* menu.c */
 void menu_set_parms(uint8_t boot_menu_flag, uint32_t boot_menu_timeout);
 int menu_get_zipl_boot_index(const char *menu_data);