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authorLaszlo Ersek <lersek@redhat.com>2017-01-26 02:44:15 +0100
committerPaolo Bonzini <pbonzini@redhat.com>2017-01-27 18:07:31 +0100
commit5ce45c7a2b15cda0a4d8f6c38c4036df25dc9c42 (patch)
tree1747e81816d133e93c5ac74f7cd0998ff23a6054 /util/fifo8.c
parent50de920b372b21e129667e16e016329d7204a7b2 (diff)
hw/isa/lpc_ich9: add broadcast SMI feature
The generic edk2 SMM infrastructure prefers EFI_SMM_CONTROL2_PROTOCOL.Trigger() to inject an SMI on each processor. If Trigger() only brings the current processor into SMM, then edk2 handles it in the following ways: (1) If Trigger() is executed by the BSP (which is guaranteed before ExitBootServices(), but is not necessarily true at runtime), then: (a) If edk2 has been configured for "traditional" SMM synchronization, then the BSP sends directed SMIs to the APs with APIC delivery, bringing them into SMM individually. Then the BSP runs the SMI handler / dispatcher. (b) If edk2 has been configured for "relaxed" SMM synchronization, then the APs that are not already in SMM are not brought in, and the BSP runs the SMI handler / dispatcher. (2) If Trigger() is executed by an AP (which is possible after ExitBootServices(), and can be forced e.g. by "taskset -c 1 efibootmgr"), then the AP in question brings in the BSP with a directed SMI, and the BSP runs the SMI handler / dispatcher. The smaller problem with (1a) and (2) is that the BSP and AP synchronization is slow. For example, the "taskset -c 1 efibootmgr" command from (2) can take more than 3 seconds to complete, because efibootmgr accesses non-volatile UEFI variables intensively. The larger problem is that QEMU's current behavior diverges from the behavior usually seen on physical hardware, and that keeps exposing obscure corner cases, race conditions and other instabilities in edk2, which generally expects / prefers a software SMI to affect all CPUs at once. Therefore introduce the "broadcast SMI" feature that causes QEMU to inject the SMI on all VCPUs. While the original posting of this patch <http://lists.nongnu.org/archive/html/qemu-devel/2015-10/msg05658.html> only intended to speed up (2), based on our recent "stress testing" of SMM this patch actually provides functional improvements. Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: Gerd Hoffmann <kraxel@redhat.com> Cc: Igor Mammedov <imammedo@redhat.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Laszlo Ersek <lersek@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Reviewed-by: Igor Mammedov <imammedo@redhat.com> Message-Id: <20170126014416.11211-3-lersek@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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