Implementation of the FW CFG DMA interface.
When running a Linux guest on top of QEMU, using the -kernel options, this is the timing improvement for x86:
QEMU commit 16a1b6e and SeaBIOS commit e4d2b8c QEMU startup time: .080 BIOS startup time: .060 Kernel setup time: .586 Total time: .726
QEMU with this patch series and SeaBIOS with this patch series QEMU startup time: .080 BIOS startup time: .039 Kernel setup time: .002 Total time: .121
QEMU startup time is the time between the start and the first kvm_entry. BIOS startup time is the time between the first kvm_entry and the start of function do_boot, in SeaBIOS. Kernel setup time is the time between the start of the function do_boot in SeaBIOS and the jump to the Linux kernel.
As you can see, both the BIOS (because of ACPI tables and other configurations) and the Linux kernel boot (because of the copy to memory) are greatly improved with this new interface.
Also, this new interface is an addon to the old interface. Both interfaces are compatible and interchangeable.
Changes from v1: - Take into account order of fields in the FWCfgDmaAccess structure - Check and change endianness of FWCfgDmaAccess fields - Change order of fields in the FWCfgDmaAccess structure - Add FW_CFG_DMA_CTL_SKIP feature for control field - Split FW_CFG_SIZE in QEMU - Make FW_CFG_ID a bitmap of features - Add 64 bit address support for the transfer. Trigger when writing the low address, and address is 0 by default and at the end of each transfer. - Align ports and addresses. - Preserve old fw_cfg_comb_valid behaviour in QEMU - Update documentation to reflect all these changes
Changes from v2: - Make IOports fw_cfg DMA region a different IO region. - Reuse everything for MMIO and IOport DMA regions - Make transfer status only based on control field - Use DMA helpers instead of direct map/unmap - Change ARM fw_cfg DMA address space - Change Linux boot process to match linuxboot.S - Add select capabilities in the FWCfgDmaAccess struct - Update documentation to reflect all these changes