On Thu, Jul 30, 2020 at 04:22:50PM +0100, Matthew Wilcox wrote: > On Mon, Jul 27, 2020 at 10:11:22AM -0700, 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, > > 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. > > I just realised that something else I'm working on might be a suitable > alternative to this. Apologies for not realising it sooner. > > http://www.wil.cx/~willy/linux/sileby.html Just skimming: make it O_CLOEXEC by default. ;) > > To use this, you'd mshare() the anonymous memory range, essentially > detaching the VMA from the current process's mm_struct and reparenting > it to this new mm_struct, which has an fd referencing it. > > Then you call exec(), and the exec'ed task gets to call mmap() on that > new fd to attach the memory range to its own address space. > > Presto!
