> -----Original Message----- > From: Paolo Bonzini [mailto:pbonzini@xxxxxxxxxx] > Sent: Wednesday, June 06, 2018 9:58 PM > To: Gonglei (Arei) <arei.gonglei@xxxxxxxxxx>; Igor Mammedov > <imammedo@xxxxxxxxxx>; xuyandong <xuyandong2@xxxxxxxxxx> > Cc: Zhanghailiang <zhang.zhanghailiang@xxxxxxxxxx>; wangxin (U) > <wangxinxin.wang@xxxxxxxxxx>; lidonglin <lidonglin@xxxxxxxxxx>; > kvm@xxxxxxxxxxxxxxx; qemu-devel@xxxxxxxxxx; Huangweidong (C) > <weidong.huang@xxxxxxxxxx> > Subject: Re: An emulation failure occurs,if I hotplug vcpus immediately after > the VM start > > On 06/06/2018 15:28, Gonglei (Arei) wrote: > > gonglei********: mem.slot: 3, mem.guest_phys_addr=0xc0000, > > mem.userspace_addr=0x7fc343ec0000, mem.flags=0, memory_size=0x0 > > gonglei********: mem.slot: 3, mem.guest_phys_addr=0xc0000, > > mem.userspace_addr=0x7fc343ec0000, mem.flags=0, > memory_size=0x9000 > > > > When the memory region is cleared, the KVM will tell the slot to be > > invalid (which it is set to KVM_MEMSLOT_INVALID). > > > > If SeaBIOS accesses this memory and cause page fault, it will find an > > invalid value according to gfn (by __gfn_to_pfn_memslot), and finally > > it will return an invalid value, and finally it will return a failure. > > > > So, My questions are: > > > > 1) Why don't we hold kvm->slots_lock during page fault processing? > > Because it's protected by SRCU. We don't need kvm->slots_lock on the read > side. > > > 2) How do we assure that vcpus will not access the corresponding > > region when deleting an memory slot? > > We don't. It's generally a guest bug if they do, but the problem here is that > QEMU is splitting a memory region in two parts and that is not atomic. > > One fix could be to add a KVM_SET_USER_MEMORY_REGIONS ioctl that > replaces the entire memory map atomically. > > Paolo After we add a KVM_SET_USER_MEMORY_REGIONS ioctl that replaces the entire memory map atomically, how to use it in address_space_update_topology? Shall we checkout the spilt memory region before " address_space_update_topology_pass(as, old_view, new_view, false); address_space_update_topology_pass(as, old_view, new_view, true); ".
