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s390: autodetect map private

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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 <borntraeger@de.ibm.com>
Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Acked-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
This commit is contained in:
Christian Borntraeger 2012-06-15 05:10:30 +00:00 • committed by Alexander Graf
parent 9233685597
commit fdec991857
5 changed files with 56 additions and 15 deletions
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18
exec.c
View file

@ -2536,26 +2536,14 @@ 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 (kvm_enabled()) {
/* some s390/kvm configurations have special constraints */
new_block->host = kvm_vmalloc(size);
} else {
new_block->host = qemu_vmalloc(size);
}
#endif
qemu_madvise(new_block->host, size, QEMU_MADV_MERGEABLE);
}
}