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kvm: Avoid COW if KVM MMU is asynchronous

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Avi Kivity wrote:
> Suggest wrapping in a function and hiding it deep inside kvm-all.c.
>

Done in v2:

---------->

If the KVM MMU is asynchronous (kernel does not support MMU_NOTIFIER),
we have to avoid COW for the guest memory. Otherwise we risk serious
breakage when guest pages change there physical locations due to COW
after fork. Seen when forking smbd during runtime via -smb.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Jan Kiszka 2009-04-26 18:03:40 +02:00 • committed by Anthony Liguori
parent 8563d5b31d
commit 6f0437e8de
3 changed files with 23 additions and 0 deletions
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18
kvm-all.c
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@ -773,6 +773,24 @@ int kvm_has_sync_mmu(void)
return 0;
}
void kvm_setup_guest_memory(void *start, size_t size)
{
if (!kvm_has_sync_mmu()) {
#ifdef MADV_DONTFORK
int ret = madvise(start, size, MADV_DONTFORK);
if (ret) {
perror("madvice");
exit(1);
}
#else
fprintf(stderr,
"Need MADV_DONTFORK in absence of synchronous KVM MMU\n");
exit(1);
#endif
}
}
#ifdef KVM_CAP_SET_GUEST_DEBUG
struct kvm_sw_breakpoint *kvm_find_sw_breakpoint(CPUState *env,
target_ulong pc)