On Mon, Jul 27, 2020 at 02:00:17PM -0400, Steven Sistare wrote: > On 7/27/2020 1:07 PM, ebiederm@xxxxxxxxxxxx wrote: > > Anthony Yznaga <anthony.yznaga@xxxxxxxxxx> writes: > > > >> 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. > > > > What is wrong with using a file descriptor to a possibly deleted file > > and re-mmaping it? > > > > There is already MAP_FIXED that allows you to ensure you have the same > > address. > > MAP_FIXED blows away any existing mapping in that range, which is not the > desired behavior. We want to preserve the previously created mapping at There's also MAP_FIXED_NOREPLACE since v4.17 in case that helps. Note that this should really go to linux-api too. I won't argue to resend it since that would mean spamming everyone's inbox with the same thread again but in case you send a revised version, please ensure to Cc linux-api. The glibc folks are listening on there too. Thanks! Christian
