[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v8 0/5] VM forking
The following series implements VM forking for Intel HVM guests to allow for the fast creation of identical VMs without the assosciated high startup costs of booting or restoring the VM from a savefile. JIRA issue: https://xenproject.atlassian.net/browse/XEN-89 The fork operation is implemented as part of the "xl fork-vm" command: xl fork-vm -C <config_file_for_fork> -Q <qemu_save_file> <parent_domid> By default a fully functional fork is created. The user is in charge however to create the appropriate config file for the fork and to generate the QEMU save file before the fork-vm call is made. The config file needs to give the fork a new name at minimum but other settings may also require changes. The interface also allows to split the forking into two steps: xl fork-vm --launch-dm no \ -p <parent_domid> xl fork-vm --launch-dm late \ -C <config_file_for_fork> \ -Q <qemu_save_file> \ <fork_domid> The split creation model is useful when the VM needs to be created as fast as possible. The forked VM can be unpaused without the device model being launched to be monitored and accessed via VMI. Note however that without its device model running (depending on what is executing in the VM) it is bound to misbehave or even crash when its trying to access devices that would be emulated by QEMU. We anticipate that for certain use-cases this would be an acceptable situation, in case for example when fuzzing is performed of code segments that don't access such devices. Launching the device model requires the QEMU Xen savefile to be generated manually from the parent VM. This can be accomplished simply by connecting to its QMP socket and issuing the "xen-save-devices-state" command. For example using the standard tool socat these commands can be used to generate the file: socat - UNIX-CONNECT:/var/run/xen/qmp-libxl-<parent_domid> { "execute": "qmp_capabilities" } { "execute": "xen-save-devices-state", \ "arguments": { "filename": "/path/to/save/qemu_state", \ "live": false} } At runtime the forked VM starts running with an empty p2m which gets lazily populated when the VM generates EPT faults, similar to how altp2m views are populated. If the memory access is a read-only access, the p2m entry is populated with a memory shared entry with its parent. For write memory accesses or in case memory sharing wasn't possible (for example in case a reference is held by a third party), a new page is allocated and the page contents are copied over from the parent VM. Forks can be further forked if needed, thus allowing for further memory savings. A VM fork reset hypercall is also added that allows the fork to be reset to the state it was just after a fork, also accessible via xl: xl fork-vm --fork-reset -p <fork_domid> This is an optimization for cases where the forks are very short-lived and run without a device model, so resetting saves some time compared to creating a brand new fork provided the fork has not aquired a lot of memory. If the fork has a lot of memory deduplicated it is likely going to be faster to create a new fork from scratch and asynchronously destroying the old one. The series has been tested with both Linux and Windows VMs and functions as expected. VM forking time has been measured to be 0.0007s, device model launch to be around 1s depending largely on the number of devices being emulated. Fork resets have been measured to be 0.0001s under the optimal circumstances. New in v8: rebase on staging and a minor fix in the toolstack code Patch 1 is a bugfix for pre-existing code in p2m Patch 2 exposes a hap internal function that will be used during VM forking Patch 3-4 implements the VM fork & reset operation hypervisor side bits Patch 5 adds the toolstack-side code implementing VM forking and reset Tamas K Lengyel (5): x86/p2m: Allow p2m_get_page_from_gfn to return shared entries xen/x86: Make hap_get_allocation accessible xen/mem_sharing: VM forking x86/mem_sharing: reset a fork xen/tools: VM forking toolstack side docs/man/xl.1.pod.in | 36 ++++ tools/libxc/include/xenctrl.h | 13 ++ tools/libxc/xc_memshr.c | 22 +++ tools/libxl/libxl.h | 7 + tools/libxl/libxl_create.c | 256 ++++++++++++++++--------- tools/libxl/libxl_dm.c | 2 +- tools/libxl/libxl_dom.c | 43 ++++- tools/libxl/libxl_internal.h | 1 + tools/libxl/libxl_types.idl | 1 + tools/xl/xl.h | 5 + tools/xl/xl_cmdtable.c | 12 ++ tools/xl/xl_saverestore.c | 97 ++++++++++ tools/xl/xl_vmcontrol.c | 8 + xen/arch/x86/domain.c | 11 ++ xen/arch/x86/hvm/hvm.c | 2 +- xen/arch/x86/mm/hap/hap.c | 3 +- xen/arch/x86/mm/mem_sharing.c | 297 ++++++++++++++++++++++++++++++ xen/arch/x86/mm/p2m.c | 25 ++- xen/include/asm-x86/hap.h | 1 + xen/include/asm-x86/mem_sharing.h | 17 ++ xen/include/public/memory.h | 6 + xen/include/xen/sched.h | 2 + 22 files changed, 763 insertions(+), 104 deletions(-) -- 2.20.1 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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