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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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35
target-s390x/kvm.c
View file

@ -135,6 +135,41 @@ int kvm_arch_get_registers(CPUS390XState *env)
return 0;
}
/*
* 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;
}
void *kvm_arch_vmalloc(ram_addr_t size)
{
/* Can we use the standard allocation ? */
if (kvm_check_extension(kvm_state, KVM_CAP_S390_GMAP) &&
kvm_check_extension(kvm_state, KVM_CAP_S390_COW)) {
return NULL;
} else {
return legacy_s390_alloc(size);
}
}
int kvm_arch_insert_sw_breakpoint(CPUS390XState *env, struct kvm_sw_breakpoint *bp)
{
static const uint8_t diag_501[] = {0x83, 0x24, 0x05, 0x01};