pc-bios: s390x: Use reset PSW if avaliable

If a blob provides a reset PSW then we should use it instead of
branching to the PSW address and using our own mask.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20201006094249.50640-4-frankja@linux.ibm.com>
[thuth: Use Elvis operator to shorten long line]
Signed-off-by: Thomas Huth <thuth@redhat.com>

3 files changed, 24 insertions, 9 deletions

diff --git a/pc-bios/s390-ccw/bootmap.c b/pc-bios/s390-ccw/bootmap.c
index 73471801de..44df7d16af 100644
--- a/pc-bios/s390-ccw/bootmap.c
+++ b/pc-bios/s390-ccw/bootmap.c
@@ -273,7 +273,8 @@ static void run_eckd_boot_script(block_number_t bmt_block_nr,
 
     IPL_assert(bms->entry[i].type == BOOT_SCRIPT_EXEC,
                "Unknown script entry type");
-    jump_to_IPL_code(bms->entry[i].address.load_address); /* no return */
+    write_reset_psw(bms->entry[i].address.load_address); /* no return */
+    jump_to_IPL_code(0); /* no return */
 }
 
 static void ipl_eckd_cdl(void)
@@ -527,7 +528,8 @@ static void zipl_run(ScsiBlockPtr *pte)
     IPL_assert(entry->component_type == ZIPL_COMP_ENTRY_EXEC, "No EXEC entry");
 
     /* should not return */
-    jump_to_IPL_code(entry->compdat.load_psw & PSW_MASK_SHORT_ADDR);
+    write_reset_psw(entry->compdat.load_psw);
+    jump_to_IPL_code(0);
 }
 
 static void ipl_scsi(void)
diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
index b6aad32def..fbae45b03c 100644
--- a/pc-bios/s390-ccw/jump2ipl.c
+++ b/pc-bios/s390-ccw/jump2ipl.c
@@ -12,15 +12,21 @@
 
 #define KERN_IMAGE_START 0x010000UL
 #define RESET_PSW_MASK (PSW_MASK_SHORTPSW | PSW_MASK_64)
+#define RESET_PSW ((uint64_t)&jump_to_IPL_addr | RESET_PSW_MASK)
 
 static uint64_t *reset_psw = 0, save_psw, ipl_continue;
 
+void write_reset_psw(uint64_t psw)
+{
+    *reset_psw = psw;
+}
+
 static void jump_to_IPL_addr(void)
 {
     __attribute__((noreturn)) void (*ipl)(void) = (void *)ipl_continue;
 
     /* Restore reset PSW */
-    *reset_psw = save_psw;
+    write_reset_psw(save_psw);
 
     ipl();
     /* should not return */
@@ -43,11 +49,12 @@ void jump_to_IPL_code(uint64_t address)
      * content of non-BIOS memory after we loaded the guest, so we
      * save the original content and restore it in jump_to_IPL_2.
      */
-    save_psw = *reset_psw;
-    *reset_psw = (uint64_t) &jump_to_IPL_addr;
-    *reset_psw |= RESET_PSW_MASK;
-    ipl_continue = address;
-    debug_print_int("set IPL addr to", ipl_continue);
+    if (address) {
+        save_psw = *reset_psw;
+        write_reset_psw(RESET_PSW);
+        ipl_continue = address;
+    }
+    debug_print_int("set IPL addr to", address ?: *reset_psw & PSW_MASK_SHORT_ADDR);
 
     /* Ensure the guest output starts fresh */
     sclp_print("\n");
@@ -77,7 +84,12 @@ void jump_to_low_kernel(void)
 
     /* Trying to get PSW at zero address */
     if (*((uint64_t *)0) & RESET_PSW_MASK) {
-        jump_to_IPL_code((*((uint64_t *)0)) & PSW_MASK_SHORT_ADDR);
+        /*
+         * Surely nobody will try running directly from lowcore, so
+         * let's use 0 as an indication that we want to load the reset
+         * psw at 0x0 and not jump to the entry.
+         */
+        jump_to_IPL_code(0);
     }
 
     /* No other option left, so use the Linux kernel start address */
diff --git a/pc-bios/s390-ccw/s390-ccw.h b/pc-bios/s390-ccw/s390-ccw.h
index 9b86c120b4..6cd92669e9 100644
--- a/pc-bios/s390-ccw/s390-ccw.h
+++ b/pc-bios/s390-ccw/s390-ccw.h
@@ -76,6 +76,7 @@ int virtio_read(ulong sector, void *load_addr);
 void zipl_load(void);
 
 /* jump2ipl.c */
+void write_reset_psw(uint64_t psw);
 void jump_to_IPL_code(uint64_t address);
 void jump_to_low_kernel(void);