[PATCH RFC v2 3/4] pc-bios: s390x: Save io and external new PSWs before overwriting them

[Janosch Frank]

Currently we always overwrite the mentioned exception new PSWs before
loading the enabled wait PSW. Let's save the PSW before overwriting
and restore it right before starting the loaded kernel.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
---

Maybe we should rather statically allocate a lowcore so we don't dirty
0x0 at all.

---
 pc-bios/s390-ccw/jump2ipl.c |  3 ++
 pc-bios/s390-ccw/start.S    | 62 +++++++++++++++++++++++++++----------
 2 files changed, 48 insertions(+), 17 deletions(-)

diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
index 143d027bf7..a44f3ab5b3 100644
--- a/pc-bios/s390-ccw/jump2ipl.c
+++ b/pc-bios/s390-ccw/jump2ipl.c
@@ -13,12 +13,15 @@
 #define KERN_IMAGE_START 0x010000UL
 #define RESET_PSW_MASK (PSW_MASK_SHORTPSW | PSW_MASK_64)
 
+extern uint64_t *psw_save_io, *psw_save_ext;
 uint64_t *reset_psw = 0, save_psw, ipl_continue;
 
 static void jump_to_IPL_2(void)
 {
     /* Restore reset PSW and io and external new PSWs */
     *reset_psw = save_psw;
+    memcpy((void *)0x1f0, psw_save_io, 16);
+    memcpy((void *)0x1b0, psw_save_ext, 16);
 
     /* No reset PSW, let's jump instead. */
     if (ipl_continue) {
diff --git a/pc-bios/s390-ccw/start.S b/pc-bios/s390-ccw/start.S
index ce519300a1..939aac3a7c 100644
--- a/pc-bios/s390-ccw/start.S
+++ b/pc-bios/s390-ccw/start.S
@@ -34,7 +34,17 @@ remainder:
        larl    %r2,memsetxc
        ex      %r3,0(%r2)
 done:
-       j      main             /* And call C */
+        /* prepare i/o call handler */
+        larl  %r1, io_new_code
+        larl  %r2, io_new_psw
+        stg   %r1, 8(%r2)
+        mvc   0x1f0(16),0(%r2)
+        /* prepare external call handler */
+        larl  %r1, external_new_code
+        larl  %r2, external_new_psw
+        stg   %r1, 8(%r2)
+        mvc   0x1b0(16),0(%r2)
+        j      main            /* And call C */
 
 memsetxc:
        xc      0(1,%r1),0(%r1)
@@ -64,13 +74,16 @@ consume_sclp_int:
         oi      6(%r15),0x2
         lctlg   %c0,%c0,0(%r15)
         /* prepare external call handler */
-        larl %r1, external_new_code
-        stg %r1, 0x1b8
-        larl %r1, external_new_mask
-        mvc 0x1b0(8),0(%r1)
-        /* load enabled wait PSW */
-        larl %r1, enabled_wait_psw
-        lpswe 0(%r1)
+        larl  %r1, external_new_psw
+        lghi  %r2, 0x1b0
+        /* Is the BIOS' external new PSW already set? */
+        clc   0(16, %r1), 0(%r2)
+        je    load_ewait
+        /* No, save old PSW and write BIOS PSW */
+        larl  %r3, psw_save_ext
+        mvc   0(16, %r3), 0x1b0
+        mvc   0x1b0(16),0(%r1)
+        j     load_ewait
 
 /*
  * void consume_io_int(void)
@@ -84,11 +97,20 @@ consume_io_int:
         oi    4(%r15), 0xff
         lctlg %c6,%c6,0(%r15)
         /* prepare i/o call handler */
-        larl  %r1, io_new_code
-        stg   %r1, 0x1f8
-        larl  %r1, io_new_mask
-        mvc   0x1f0(8),0(%r1)
-        /* load enabled wait PSW */
+        larl  %r1, io_new_psw
+        lghi  %r2, 0x1f0
+        /* Is the BIOS' PSW already set? */
+        larl  %r3, load_ewait
+        clc   0(16, %r1), 0(%r2)
+        bcr   8, %r3
+        /* No, save old PSW and write BIOS PSW */
+        larl  %r3, psw_save_io
+        mvc   0(16, %r3), 0x1f0
+        mvc   0x1f0(16),0(%r1)
+        j     load_ewait
+
+load_ewait:
+        /* PSW is the correct one, time to load the enabled wait PSW */
         larl  %r1, enabled_wait_psw
         lpswe 0(%r1)
 
@@ -107,11 +129,17 @@ io_new_code:
         br    %r14
 
         .align  8
+        .globl psw_save_io
+        .globl psw_save_ext
 disabled_wait_psw:
         .quad   0x0002000180000000,0x0000000000000000
 enabled_wait_psw:
         .quad   0x0302000180000000,0x0000000000000000
-external_new_mask:
-        .quad   0x0000000180000000
-io_new_mask:
-        .quad   0x0000000180000000
+external_new_psw:
+        .quad   0x0000000180000000,0
+io_new_psw:
+        .quad   0x0000000180000000,0
+psw_save_io:
+        .quad   0,0
+psw_save_ext:
+        .quad   0,0
-- 
2.25.1