From 57ba0792ca430557ec89aa3daeceb42034161706 Mon Sep 17 00:00:00 2001 From: Jan Kiszka Date: Sun, 26 Apr 2009 18:03:40 +0200 Subject: [PATCH] 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 Signed-off-by: Anthony Liguori --- exec.c | 4 ++++ kvm-all.c | 18 ++++++++++++++++++ kvm.h | 2 ++ 3 files changed, 24 insertions(+) diff --git a/exec.c b/exec.c index 37468399fc1..61a55325ef8 100644 --- a/exec.c +++ b/exec.c @@ -2386,6 +2386,10 @@ ram_addr_t qemu_ram_alloc(ram_addr_t size) } addr = phys_ram_alloc_offset; phys_ram_alloc_offset = TARGET_PAGE_ALIGN(phys_ram_alloc_offset + size); + + if (kvm_enabled()) + kvm_setup_guest_memory(phys_ram_base + addr, size); + return addr; } diff --git a/kvm-all.c b/kvm-all.c index 28c9c07ccbd..2b7d5350304 100644 --- a/kvm-all.c +++ b/kvm-all.c @@ -656,3 +656,21 @@ 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 + } +} diff --git a/kvm.h b/kvm.h index efce1450d59..5a52f51cb90 100644 --- a/kvm.h +++ b/kvm.h @@ -46,6 +46,8 @@ int kvm_log_stop(target_phys_addr_t phys_addr, target_phys_addr_t len); 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); -- 2.39.5