Commit 6f0437e8 authored by Jan Kiszka's avatar Jan Kiszka Committed by Anthony Liguori
Browse files

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: default avatarJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: default avatarAnthony Liguori <aliguori@us.ibm.com>
parent 8563d5b3

exec.c

+3 −0
Original line number Diff line number Diff line
@@ -2484,6 +2484,9 @@ ram_addr_t qemu_ram_alloc(ram_addr_t size) 


    last_ram_offset += size;



    if (kvm_enabled())

        kvm_setup_guest_memory(new_block->host, size);



    return new_block->offset;

}

kvm-all.c

+18 −0
Original line number Diff line number Diff line
@@ -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)

kvm.h

+2 −0
Original line number Diff line number Diff line
@@ -48,6 +48,8 @@ int kvm_log_stop(target_phys_addr_t phys_addr, ram_addr_t size); 


int kvm_has_sync_mmu(void);



void kvm_setup_guest_memory(void *start, size_t size);



int kvm_coalesce_mmio_region(target_phys_addr_t start, ram_addr_t size);

int kvm_uncoalesce_mmio_region(target_phys_addr_t start, ram_addr_t size);