s390/vmcp: make use of contiguous memory allocator

If memory is fragmented it is unlikely that large order memory
allocations succeed. This has been an issue with the vmcp device
driver since a long time, since it requires large physical contiguous
memory ares for large responses.

To hopefully resolve this issue make use of the contiguous memory
allocator (cma). This patch adds a vmcp specific vmcp cma area with a
default size of 4MB. The size can be changed either via the
VMCP_CMA_SIZE config option at compile time or with the "vmcp_cma"
kernel parameter (e.g. "vmcp_cma=16m").

For any vmcp response buffers larger than 16k memory from the cma area
will be allocated. If such an allocation fails, there is a fallback to
the buddy allocator.

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

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index d9c171c..5a2d507 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4375,6 +4375,10 @@
                        decrease the size and leave more room for directly
                        mapped kernel RAM.
 
+       vmcp_cma=nn[MG] [KNL,S390]
+                       Sets the memory size reserved for contiguous memory
+                       allocations for the vmcp device driver.
+
        vmhalt=         [KNL,S390] Perform z/VM CP command after system halt.
                        Format: <command>
 

diff --git a/arch/s390/include/asm/setup.h b/arch/s390/include/asm/setup.h
index 61da4bd..490e035 100644 (file)
--- a/arch/s390/include/asm/setup.h
+++ b/arch/s390/include/asm/setup.h
@@ -108,6 +108,12 @@ extern void pfault_fini(void);
 #define pfault_fini()          do { } while (0)
 #endif /* CONFIG_PFAULT */
 
+#ifdef CONFIG_VMCP
+void vmcp_cma_reserve(void);
+#else
+static inline void vmcp_cma_reserve(void) { }
+#endif
+
 void report_user_fault(struct pt_regs *regs, long signr, int is_mm_fault);
 
 void cmma_init(void);

diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index a50238e..164a1e1 100644 (file)
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -925,6 +925,7 @@ void __init setup_arch(char **cmdline_p)
        setup_memory_end();
        setup_memory();
        dma_contiguous_reserve(memory_end);
+       vmcp_cma_reserve();
 
        check_initrd();
        reserve_crashkernel();

diff --git a/drivers/s390/char/Kconfig b/drivers/s390/char/Kconfig
index b3f1c45..97c4c9f 100644 (file)
--- a/drivers/s390/char/Kconfig
+++ b/drivers/s390/char/Kconfig
@@ -169,10 +169,21 @@ config VMCP
        def_bool y
        prompt "Support for the z/VM CP interface"
        depends on S390
+       select CMA
        help
          Select this option if you want to be able to interact with the control
          program on z/VM
 
+config VMCP_CMA_SIZE
+       int "Memory in MiB reserved for z/VM CP interface"
+       default "4"
+       depends on VMCP
+       help
+         Specify the default amount of memory in MiB reserved for the z/VM CP
+         interface. If needed this memory is used for large contiguous memory
+         allocations. The default can be changed with the kernel command line
+         parameter "vmcp_cma".
+
 config MONREADER
        def_tristate m
        prompt "API for reading z/VM monitor service records"

diff --git a/drivers/s390/char/vmcp.c b/drivers/s390/char/vmcp.c
index b5e3a49..c202b40 100644 (file)
--- a/drivers/s390/char/vmcp.c
+++ b/drivers/s390/char/vmcp.c
@@ -17,15 +17,77 @@
 #include <linux/kernel.h>
 #include <linux/miscdevice.h>
 #include <linux/slab.h>
+#include <linux/uaccess.h>
 #include <linux/export.h>
+#include <linux/mutex.h>
+#include <linux/cma.h>
+#include <linux/mm.h>
 #include <asm/compat.h>
 #include <asm/cpcmd.h>
 #include <asm/debug.h>
-#include <linux/uaccess.h>
 #include "vmcp.h"
 
 static debug_info_t *vmcp_debug;
 
+static unsigned long vmcp_cma_size __initdata = CONFIG_VMCP_CMA_SIZE * 1024 * 1024;
+static struct cma *vmcp_cma;
+
+static int __init early_parse_vmcp_cma(char *p)
+{
+       vmcp_cma_size = ALIGN(memparse(p, NULL), PAGE_SIZE);
+       return 0;
+}
+early_param("vmcp_cma", early_parse_vmcp_cma);
+
+void __init vmcp_cma_reserve(void)
+{
+       if (!MACHINE_IS_VM)
+               return;
+       cma_declare_contiguous(0, vmcp_cma_size, 0, 0, 0, false, "vmcp", &vmcp_cma);
+}
+
+static void vmcp_response_alloc(struct vmcp_session *session)
+{
+       struct page *page = NULL;
+       int nr_pages, order;
+
+       order = get_order(session->bufsize);
+       nr_pages = ALIGN(session->bufsize, PAGE_SIZE) >> PAGE_SHIFT;
+       /*
+        * For anything below order 3 allocations rely on the buddy
+        * allocator. If such low-order allocations can't be handled
+        * anymore the system won't work anyway.
+        */
+       if (order > 2)
+               page = cma_alloc(vmcp_cma, nr_pages, 0, GFP_KERNEL);
+       if (page) {
+               session->response = (char *)page_to_phys(page);
+               session->cma_alloc = 1;
+               return;
+       }
+       session->response = (char *)__get_free_pages(GFP_KERNEL | __GFP_RETRY_MAYFAIL, order);
+}
+
+static void vmcp_response_free(struct vmcp_session *session)
+{
+       int nr_pages, order;
+       struct page *page;
+
+       if (!session->response)
+               return;
+       order = get_order(session->bufsize);
+       nr_pages = ALIGN(session->bufsize, PAGE_SIZE) >> PAGE_SHIFT;
+       if (session->cma_alloc) {
+               page = phys_to_page((unsigned long)session->response);
+               cma_release(vmcp_cma, page, nr_pages);
+               session->cma_alloc = 0;
+               goto out;
+       }
+       free_pages((unsigned long)session->response, order);
+out:
+       session->response = NULL;
+}
+
 static int vmcp_open(struct inode *inode, struct file *file)
 {
        struct vmcp_session *session;
@@ -51,7 +113,7 @@ static int vmcp_release(struct inode *inode, struct file *file)
 
        session = file->private_data;
        file->private_data = NULL;
-       free_pages((unsigned long)session->response, get_order(session->bufsize));
+       vmcp_response_free(session);
        kfree(session);
        return 0;
 }
@@ -97,9 +159,7 @@ vmcp_write(struct file *file, const char __user *buff, size_t count,
                return -ERESTARTSYS;
        }
        if (!session->response)
-               session->response = (char *)__get_free_pages(GFP_KERNEL
-                                               | __GFP_RETRY_MAYFAIL,
-                                               get_order(session->bufsize));
+               vmcp_response_alloc(session);
        if (!session->response) {
                mutex_unlock(&session->mutex);
                kfree(cmd);
@@ -146,9 +206,7 @@ static long vmcp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
                mutex_unlock(&session->mutex);
                return put_user(temp, argp);
        case VMCP_SETBUF:
-               free_pages((unsigned long)session->response,
-                               get_order(session->bufsize));
-               session->response=NULL;
+               vmcp_response_free(session);
                temp = get_user(session->bufsize, argp);
                if (temp)
                        session->bufsize = PAGE_SIZE;

diff --git a/drivers/s390/char/vmcp.h b/drivers/s390/char/vmcp.h
index 1e29b04..4e725ed 100644 (file)
--- a/drivers/s390/char/vmcp.h
+++ b/drivers/s390/char/vmcp.h
@@ -20,8 +20,9 @@
 #define VMCP_GETSIZE _IOR(0x10, 3, int)
 
 struct vmcp_session {
-       unsigned int bufsize;
        char *response;
+       unsigned int bufsize;
+       unsigned int cma_alloc : 1;
        int resp_size;
        int resp_code;
        /* As we use copy_from/to_user, which might     *