Hi, Sorry in advance, if wrong maillist.
Where may I find comprehensive description how virtualization CPU extensions (like VMX) interact with CPU data caches as well as corresponding qemu implementation details? I've looked through memory_ldst.inc.c with little success. I am trying to debug virtio_blk issues found on Xeon X5675. I run nested guest under qemu-kvm from ESXi 5.5 hosted guest, this is quite odd setup but still. Currently (master qemu, host and guest - 4.15 kernel), virtio is broken in this setup due to some kind of memory synchronization issues. Let me please recall, that main virtio communication abstraction is a queue. The queue is consisted from three parts: descriptor table, avail ring, used ring. This structures are supposed to be shared memory between the guest and the hypervisor. All of them are structures allocated by the guest device driver, pointers in guest physical address space are transferred to the hypervisor through PCI MMIO configuration BAR. This is so-called modern PCI virtio. When the guest wants to notify the hypervisor for update, the guest device driver writes to PCI BAR. At the hypervisor side, notification is implemented through eventfd and KVM_IOEVENTFD ioctl. It works as expected, since I see that qemu receives a lot of notification for the queue. However, qemu sees no updates in avail ring where guest driver increments so called "avail index" at each transfer. At the hypervisor side avail ring index is always 1, so as virtio_queue_empty_rcu() always says that incoming queue is empty one.
