From: Christian Borntraeger <borntrae...@de.ibm.com>
By default qemu will use MAP_PRIVATE for guest pages. This will write
protect pages and thus break on s390 systems that dont support this feature.
Therefore qemu has a hack to always use MAP_SHARED for s390. But MAP_SHARED
has other problems (no dirty pages tracking, a lot more swap overhead etc.)
Newer systems allow the distinction via KVM_CAP_S390_COW. With this feature
qemu can use the standard qemu alloc if available, otherwise it will use
the old s390 hack.
Signed-off-by: Christian Borntraeger <borntrae...@de.ibm.com>
Signed-off-by: Jens Freimann <jf...@linux.vnet.ibm.com>
---
exec.c | 54 +++++++++++++++++++++++++++++++++++++---------------
kvm.h | 9 +++++++++
oslib-posix.c | 3 +++
target-s390x/kvm.c | 6 ++++++
4 files changed, 57 insertions(+), 15 deletions(-)
diff --git a/exec.c b/exec.c
index a0494c7..8fec680 100644
--- a/exec.c
+++ b/exec.c
@@ -2618,6 +2618,43 @@ void qemu_ram_set_idstr(ram_addr_t addr, const char
*name, DeviceState *dev)
}
}
+/*
+ * lets make sure that we dont have the old s390x limitations regarding
+ * guest mappings
+ */
+static int legacy_s390x_mem_layout(void)
+{
+#if defined(TARGET_S390X)
+ return kvm_has_legacy_s390x_memlayout();
+#else
+ return 0;
+#endif
+}
+
+/*
+ * Legacy layout for s390:
+ * Older S390 KVM requires the topmost vma of the RAM to be
+ * smaller than an system defined value, which is at least 256GB.
+ * Larger systems have larger values. We put the guest between
+ * the end of data segment (system break) and this value. We
+ * use 32GB as a base to have enough room for the system break
+ * to grow. We also have to use MAP parameters that avoid
+ * read-only mapping of guest pages.
+ */
+static void *legacy_s390_alloc(ram_addr_t size)
+{
+ void *mem;
+
+ mem = mmap((void *) 0x800000000ULL, size,
+ PROT_EXEC|PROT_READ|PROT_WRITE,
+ MAP_SHARED | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
+ if (mem == MAP_FAILED) {
+ fprintf(stderr, "Allocating RAM failed\n");
+ abort();
+ }
+ return mem;
+}
+
ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
MemoryRegion *mr)
{
@@ -2644,26 +2681,13 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size,
void *host,
exit(1);
#endif
} else {
-#if defined(TARGET_S390X) && defined(CONFIG_KVM)
- /* S390 KVM requires the topmost vma of the RAM to be smaller than
- an system defined value, which is at least 256GB. Larger systems
- have larger values. We put the guest between the end of data
- segment (system break) and this value. We use 32GB as a base to
- have enough room for the system break to grow. */
- new_block->host = mmap((void*)0x800000000, size,
- PROT_EXEC|PROT_READ|PROT_WRITE,
- MAP_SHARED | MAP_ANONYMOUS | MAP_FIXED, -1,
0);
- if (new_block->host == MAP_FAILED) {
- fprintf(stderr, "Allocating RAM failed\n");
- abort();
- }
-#else
if (xen_enabled()) {
xen_ram_alloc(new_block->offset, size, mr);
+ } else if (legacy_s390x_mem_layout()) {
+ new_block->host = legacy_s390_alloc(size);
} else {
new_block->host = qemu_vmalloc(size);
}
-#endif
qemu_madvise(new_block->host, size, QEMU_MADV_MERGEABLE);
}
}
diff --git a/kvm.h b/kvm.h
index 9c7b0ea..ca0557e 100644
--- a/kvm.h
+++ b/kvm.h
@@ -62,6 +62,15 @@ int kvm_has_pit_state2(void);
int kvm_has_many_ioeventfds(void);
int kvm_has_gsi_routing(void);
+#ifndef CONFIG_KVM
+static inline int kvm_has_legacy_s390x_memlayout(void)
+{
+ return 0;
+}
+#else
+int kvm_has_legacy_s390x_memlayout(void);
+#endif
+
int kvm_allows_irq0_override(void);
#ifdef NEED_CPU_H
diff --git a/oslib-posix.c b/oslib-posix.c
index b6a3c7f..93902ac 100644
--- a/oslib-posix.c
+++ b/oslib-posix.c
@@ -41,6 +41,9 @@ extern int daemon(int, int);
therefore we need special code which handles running on Valgrind. */
# define QEMU_VMALLOC_ALIGN (512 * 4096)
# define CONFIG_VALGRIND
+#elif defined(__linux__) && defined(__s390x__)
+ /* Use 1 MiB (segment size) alignment so gmap can be used by KVM. */
+# define QEMU_VMALLOC_ALIGN (256 * 4096)
#else
# define QEMU_VMALLOC_ALIGN getpagesize()
#endif
diff --git a/target-s390x/kvm.c b/target-s390x/kvm.c
index 90aad61..93a8431 100644
--- a/target-s390x/kvm.c
+++ b/target-s390x/kvm.c
@@ -135,6 +135,12 @@ int kvm_arch_get_registers(CPUS390XState *env)
return 0;
}
+int kvm_has_legacy_s390x_memlayout(void)
+{
+ return !kvm_check_extension(kvm_state, KVM_CAP_S390_GMAP) ||
+ !kvm_check_extension(kvm_state, KVM_CAP_S390_COW);
+}
+
int kvm_arch_insert_sw_breakpoint(CPUS390XState *env, struct kvm_sw_breakpoint
*bp)
{
static const uint8_t diag_501[] = {0x83, 0x24, 0x05, 0x01};
--
1.7.10.4
