gwj / at91sam9263 · Commits

Commit 6f0437e8de95aebbd9e66af4d074c0d5119d86b7

Authored by Jan Kiszka
Committed by Anthony Liguori
1 parent 8563d5b3

kvm: Avoid COW if KVM MMU is asynchronous 

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>
Inline Side-by-side
Showing 3 changed files with 23 additions and 0 deletions
... ... @@ -2484,6 +2484,9 @@ ram_addr_t qemu_ram_alloc(ram_addr_t size)
2484 2484  
2485 2485 last_ram_offset += size;
2486 2486  
  2487 + if (kvm_enabled())
  2488 + kvm_setup_guest_memory(new_block->host, size);
  2489 +
2487 2490 return new_block->offset;
2488 2491 }
2489 2492  
... ...
kvm-all.c
  View file @6f0437e
... ... @@ -773,6 +773,24 @@ int kvm_has_sync_mmu(void)
773 773 return 0;
774 774 }
775 775  
  776 +void kvm_setup_guest_memory(void *start, size_t size)
  777 +{
  778 + if (!kvm_has_sync_mmu()) {
  779 +#ifdef MADV_DONTFORK
  780 + int ret = madvise(start, size, MADV_DONTFORK);
  781 +
  782 + if (ret) {
  783 + perror("madvice");
  784 + exit(1);
  785 + }
  786 +#else
  787 + fprintf(stderr,
  788 + "Need MADV_DONTFORK in absence of synchronous KVM MMU\n");
  789 + exit(1);
  790 +#endif
  791 + }
  792 +}
  793 +
776 794 #ifdef KVM_CAP_SET_GUEST_DEBUG
777 795 struct kvm_sw_breakpoint *kvm_find_sw_breakpoint(CPUState *env,
778 796 target_ulong pc)
... ...
... ... @@ -48,6 +48,8 @@ int kvm_log_stop(target_phys_addr_t phys_addr, ram_addr_t size);
48 48  
49 49 int kvm_has_sync_mmu(void);
50 50  
  51 +void kvm_setup_guest_memory(void *start, size_t size);
  52 +
51 53 int kvm_coalesce_mmio_region(target_phys_addr_t start, ram_addr_t size);
52 54 int kvm_uncoalesce_mmio_region(target_phys_addr_t start, ram_addr_t size);
53 55  
... ...