[PATCH] s390x/ipl: support extended kernel command line size

[Marc Hartmayer <mhartmay@linux.ibm.com>]

In the past s390 used a fixed command line length of 896 bytes. This has changed
with the Linux commit 5ecb2da660ab ("s390: support command lines longer than 896
bytes"). There is now a parm area indicating the maximum command line size. This
parm area has always been initialized to zero, so with older kernels this field
would read zero and we must then assume that only 896 bytes are available.

Acked-by: Viktor Mihajlovski <mihajlov@de.ibm.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
---
 hw/s390x/ipl.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/hw/s390x/ipl.c b/hw/s390x/ipl.c
index 7ddca0127fc2..092c66b3f9f1 100644
--- a/hw/s390x/ipl.c
+++ b/hw/s390x/ipl.c
@@ -37,8 +37,9 @@
 
 #define KERN_IMAGE_START                0x010000UL
 #define LINUX_MAGIC_ADDR                0x010008UL
+#define KERN_PARM_AREA_SIZE_ADDR        0x010430UL
 #define KERN_PARM_AREA                  0x010480UL
-#define KERN_PARM_AREA_SIZE             0x000380UL
+#define LEGACY_KERN_PARM_AREA_SIZE      0x000380UL
 #define INITRD_START                    0x800000UL
 #define INITRD_PARM_START               0x010408UL
 #define PARMFILE_START                  0x001000UL
@@ -110,6 +111,21 @@ static uint64_t bios_translate_addr(void *opaque, uint64_t srcaddr)
     return srcaddr + dstaddr;
 }
 
+static uint64_t get_max_kernel_cmdline_size(void)
+{
+    uint64_t *size_ptr = rom_ptr(KERN_PARM_AREA_SIZE_ADDR, sizeof(*size_ptr));
+
+    if (size_ptr) {
+        uint64_t size;
+
+        size = be64_to_cpu(*size_ptr);
+        if (size != 0) {
+            return size;
+        }
+    }
+    return LEGACY_KERN_PARM_AREA_SIZE;
+}
+
 static void s390_ipl_realize(DeviceState *dev, Error **errp)
 {
     MachineState *ms = MACHINE(qdev_get_machine());
@@ -197,10 +213,11 @@ static void s390_ipl_realize(DeviceState *dev, Error **errp)
             ipl->start_addr = KERN_IMAGE_START;
             /* Overwrite parameters in the kernel image, which are "rom" */
             if (parm_area) {
-                if (cmdline_size > KERN_PARM_AREA_SIZE) {
+                uint64_t max_cmdline_size = get_max_kernel_cmdline_size();
+                if (cmdline_size > max_cmdline_size) {
                     error_setg(errp,
                                "kernel command line exceeds maximum size: %zu > %lu",
-                               cmdline_size, KERN_PARM_AREA_SIZE);
+                               cmdline_size, max_cmdline_size);
                     return;
                 }
 
-- 
2.31.1