According to the TLFS: "A write to the end of message (EOM) register by the guest causes the hypervisor to scan the internal message buffer queue(s) associated with the virtual processor. If a message buffer queue contains a queued message buffer, the hypervisor attempts to deliver the message. Message delivery succeeds if the SIM page is enabled and the message slot corresponding to the SINTx is empty (that is, the message type in the header is set to HvMessageTypeNone). If a message is successfully delivered, its corresponding internal message buffer is dequeued and marked free. If the corresponding SINTx is not masked, an edge-triggered interrupt is delivered (that is, the corresponding bit in the IRR is set). This register can be used by guests to poll for messages. It can also be used as a way to drain the message queue for a SINTx that has been disabled (that is, masked)." So basically this means that we need to exit on EOM so the hypervisor will have a chance to send all the pending messages regardless of the SCONTROL mechnaisim. Jon Doron (1): x86/kvm/hyper-v: Add support to SYNIC exit on EOM arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/hyperv.c | 65 +++++++++++++++++++++++++++++---- arch/x86/kvm/hyperv.h | 1 + arch/x86/kvm/x86.c | 5 +++ include/uapi/linux/kvm.h | 1 + 5 files changed, 65 insertions(+), 8 deletions(-) -- 2.24.1
