On 7/28/20 4:34 AM, Kirill Tkhai wrote: > On 27.07.2020 20:11, Anthony Yznaga wrote: >> This patchset adds support for preserving an anonymous memory range across >> exec(3) using a new madvise MADV_DOEXEC argument. The primary benefit for >> sharing memory in this manner, as opposed to re-attaching to a named shared >> memory segment, is to ensure it is mapped at the same virtual address in >> the new process as it was in the old one. An intended use for this is to >> preserve guest memory for guests using vfio while qemu exec's an updated >> version of itself. By ensuring the memory is preserved at a fixed address, > So, the goal is an update of QEMU binary without a stopping of virtual machine? Essentially, yes. The VM is paused very briefly. Anthony > >> vfio mappings and their associated kernel data structures can remain valid. >> In addition, for the qemu use case, qemu instances that back guest RAM with >> anonymous memory can be updated. >> >> Patches 1 and 2 ensure that loading of ELF load segments does not silently >> clobber existing VMAS, and remove assumptions that the stack is the only >> VMA in the mm when the stack is set up. Patch 1 re-introduces the use of >> MAP_FIXED_NOREPLACE to load ELF binaries that addresses the previous issues >> and could be considered on its own. >> >> Patches 3, 4, and 5 introduce the feature and an opt-in method for its use >> using an ELF note. >> >> Anthony Yznaga (5): >> elf: reintroduce using MAP_FIXED_NOREPLACE for elf executable mappings >> mm: do not assume only the stack vma exists in setup_arg_pages() >> mm: introduce VM_EXEC_KEEP >> exec, elf: require opt-in for accepting preserved mem >> mm: introduce MADV_DOEXEC >> >> arch/x86/Kconfig | 1 + >> fs/binfmt_elf.c | 196 +++++++++++++++++++++++++-------- >> fs/exec.c | 33 +++++- >> include/linux/binfmts.h | 7 +- >> include/linux/mm.h | 5 + >> include/uapi/asm-generic/mman-common.h | 3 + >> kernel/fork.c | 2 +- >> mm/madvise.c | 25 +++++ >> mm/mmap.c | 47 ++++++++ >> 9 files changed, 266 insertions(+), 53 deletions(-) >>
