From: Heiko Carstens <heiko.carstens@de.ibm.com>
Subject: s390/cpcmd,vmcp: avoid GFP_DMA allocations
Patch-mainline: v4.14-rc1
Git-commit: cd4386a931b6310b05559d2e28efda04d30ab593
References: bnc#1066983, LTC#159112

Description:  vmcp: avoid GFP_DMA allocations
Symptom:      The vmcp tool fails to execute a cp command because the kernel
              was unable to allocate memory.
Problem:      Allocation of memory for the response area of the diagnose 8
              command is done with GFP_DMA. If memory is fragmented, large
              order allocations can likely fail and this causes vmcp to fail.
Solution:     Remove the GFP_DMA requirement since it is not needed anymore.
              This makes it more likely that the allocation will succeed,
              since also other memory zones will be considered for memory
              allocation.
              There is still no guarantee that the allocation will succeed,
              however with this change it is less likely to see allocation
              failures.
Reproduction: -

Upstream-Description:

              s390/cpcmd,vmcp: avoid GFP_DMA allocations

              According to the CP Programming Services manual Diagnose Code 8
              "Virtual Console Function" can be used in all addressing modes. Also
              the input and output buffers do not have a limitation which specifies
              they need to be below the 2GB line.

              This is true at least since z/VM 5.4.

              Therefore remove the sam31/64 instructions and allow for simple
              GFP_KERNEL allocations. This makes it easier to allocate a 1MB page
              if the user requested such a large return buffer.

              Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
              Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>


Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 arch/s390/include/asm/cpcmd.h |    7 +++----
 arch/s390/kernel/cpcmd.c      |   13 ++++---------
 drivers/s390/char/vmcp.c      |    2 +-
 3 files changed, 8 insertions(+), 14 deletions(-)

--- a/arch/s390/include/asm/cpcmd.h
+++ b/arch/s390/include/asm/cpcmd.h
@@ -10,9 +10,8 @@
 
 /*
  * the lowlevel function for cpcmd
- * the caller of __cpcmd has to ensure that the response buffer is below 2 GB
  */
-extern int __cpcmd(const char *cmd, char *response, int rlen, int *response_code);
+int __cpcmd(const char *cmd, char *response, int rlen, int *response_code);
 
 /*
  * cpcmd is the in-kernel interface for issuing CP commands
@@ -25,8 +24,8 @@ extern int __cpcmd(const char *cmd, char
  * response_code: return pointer for VM's error code
  * return value: the size of the response. The caller can check if the buffer
  *		was large enough by comparing the return value and rlen
- * NOTE: If the response buffer is not below 2 GB, cpcmd can sleep
+ * NOTE: If the response buffer is not in real storage, cpcmd can sleep
  */
-extern int cpcmd(const char *cmd, char *response, int rlen, int *response_code);
+int cpcmd(const char *cmd, char *response, int rlen, int *response_code);
 
 #endif /* _ASM_S390_CPCMD_H */
--- a/arch/s390/kernel/cpcmd.c
+++ b/arch/s390/kernel/cpcmd.c
@@ -14,6 +14,7 @@
 #include <linux/spinlock.h>
 #include <linux/stddef.h>
 #include <linux/string.h>
+#include <linux/mm.h>
 #include <asm/diag.h>
 #include <asm/ebcdic.h>
 #include <asm/cpcmd.h>
@@ -28,9 +29,7 @@ static int diag8_noresponse(int cmdlen)
 	register unsigned long reg3 asm ("3") = cmdlen;
 
 	asm volatile(
-		"	sam31\n"
 		"	diag	%1,%0,0x8\n"
-		"	sam64\n"
 		: "+d" (reg3) : "d" (reg2) : "cc");
 	return reg3;
 }
@@ -43,9 +42,7 @@ static int diag8_response(int cmdlen, ch
 	register unsigned long reg5 asm ("5") = *rlen;
 
 	asm volatile(
-		"	sam31\n"
 		"	diag	%2,%0,0x8\n"
-		"	sam64\n"
 		"	brc	8,1f\n"
 		"	agr	%1,%4\n"
 		"1:\n"
@@ -57,7 +54,6 @@ static int diag8_response(int cmdlen, ch
 
 /*
  * __cpcmd has some restrictions over cpcmd
- *  - the response buffer must reside below 2GB (if any)
  *  - __cpcmd is unlocked and therefore not SMP-safe
  */
 int  __cpcmd(const char *cmd, char *response, int rlen, int *response_code)
@@ -88,13 +84,12 @@ EXPORT_SYMBOL(__cpcmd);
 
 int cpcmd(const char *cmd, char *response, int rlen, int *response_code)
 {
+	unsigned long flags;
 	char *lowbuf;
 	int len;
-	unsigned long flags;
 
-	if ((virt_to_phys(response) != (unsigned long) response) ||
-			(((unsigned long)response + rlen) >> 31)) {
-		lowbuf = kmalloc(rlen, GFP_KERNEL | GFP_DMA);
+	if (is_vmalloc_or_module_addr(response)) {
+		lowbuf = kmalloc(rlen, GFP_KERNEL);
 		if (!lowbuf) {
 			pr_warn("The cpcmd kernel function failed to allocate a response buffer\n");
 			return -ENOMEM;
--- a/drivers/s390/char/vmcp.c
+++ b/drivers/s390/char/vmcp.c
@@ -98,7 +98,7 @@ vmcp_write(struct file *file, const char
 	}
 	if (!session->response)
 		session->response = (char *)__get_free_pages(GFP_KERNEL
-						| __GFP_REPEAT | GFP_DMA,
+						| __GFP_REPEAT,
 						get_order(session->bufsize));
 	if (!session->response) {
 		mutex_unlock(&session->mutex);