[PATCH v3] s390/iomem: register initrd as an iomem resource when retain_initrd is set

Currently, /proc/iomem contains no reference to initrd memory, even
when initrd is retained and still held in RAM. This makes the memory
ranges invisible from userspace, and unusable to programs such as
kexec. (A sysfs bin file is created for initrd, but this doesn't
help programs which need the explicit memory ranges)

Add initrd to standard_resources[] unconditionally. Add initrd as a
child of iomem_resources only if retain_initrd is specified.

strstr() could match substrings like "retain_initrd=0" or
"no_retain_initrd", but this is how PPC chose to check for
"retain_initrd" param too. (arch/powerpc/kexec/ranges.c)

Signed-off-by: Joseph Cathcart <[email protected]>
---
 arch/s390/kernel/setup.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index b60284328fe3..45b0e19bdab2 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -481,15 +481,22 @@ static struct resource bss_resource = {
 	.flags = IORESOURCE_BUSY | IORESOURCE_SYSTEM_RAM,
 };
 
+static struct resource initrd_resource = {
+	.name = "initrd",
+	.flags = IORESOURCE_BUSY | IORESOURCE_SYSTEM_RAM,
+};
+
 static struct resource __initdata *standard_resources[] = {
 	&code_resource,
 	&data_resource,
 	&bss_resource,
+	&initrd_resource,
 };
 
 static void __init setup_resources(void)
 {
 	struct resource *res, *std_res, *sub_res;
+	bool retain_initrd = false;
 	phys_addr_t start, end;
 	int j;
 	u64 i;
@@ -501,6 +508,19 @@ static void __init setup_resources(void)
 	bss_resource.start = __pa_symbol(__bss_start);
 	bss_resource.end = __pa_symbol(__bss_stop) - 1;
 
+	if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && retain_initrd) {
+		unsigned long initrd_addr, initrd_size;
+	
+		if (strstr(boot_command_line, "retain_initrd"))
+			retain_initrd = true;
+		if (get_physmem_reserved(RR_INITRD, &initrd_addr, &initrd_size)) {
+			initrd_resource.start = initrd_addr;
+			initrd_resource.end = initrd_resource.start + initrd_size - 1;
+		} else {
+			retain_initrd = false;
+		}
+	}
+
 	for_each_mem_range(i, &start, &end) {
 		res = memblock_alloc_or_panic(sizeof(*res), 8);
 		res->flags = IORESOURCE_BUSY | IORESOURCE_SYSTEM_RAM;
@@ -517,6 +537,8 @@ static void __init setup_resources(void)
 
 		for (j = 0; j < ARRAY_SIZE(standard_resources); j++) {
 			std_res = standard_resources[j];
+			if (std_res == &initrd_resource && !retain_initrd)
+				continue;
 			if (std_res->start < res->start ||
 			    std_res->start > res->end)
 				continue;
-- 
2.55.0

base commit: 0f23d56f17fdfc7db69d51f64c8b91bbab947aa9