On Tue, Feb 09, 2021 at 02:17:11PM +0100, Michal Hocko wrote: > On Tue 09-02-21 11:09:38, Mike Rapoport wrote: > > On Tue, Feb 09, 2021 at 09:47:08AM +0100, Michal Hocko wrote: > > > > > > OK, so IIUC this means that the model is to hand over memory from host > > > to guest. I thought the guest would be under control of its address > > > space and therefore it operates on the VMAs. This would benefit from > > > an additional and more specific clarification. > > > > How guest would operate on VMAs if the interface between host and guest is > > virtual hardware? > > I have to say that I am not really familiar with this area so my view > might be misleading or completely wrong. I thought that the HW address > ranges are mapped to the guest process and therefore have a VMA. There is a qemu process that currently has mappings of what guest sees as its physical memory, but qemu is a part of hypervisor, i.e. host. > > Citing my older email: > > > > I've hesitated whether to continue to use new flags to memfd_create() or to > > add a new system call and I've decided to use a new system call after I've > > started to look into man pages update. There would have been two completely > > independent descriptions and I think it would have been very confusing. > > Could you elaborate? Unmapping from the kernel address space can work > both for sealed or hugetlb memfds, no? Those features are completely > orthogonal AFAICS. With a dedicated syscall you will need to introduce > this functionality on top if that is required. Have you considered that? > I mean hugetlb pages are used to back guest memory very often. Is this > something that will be a secret memory usecase? > > Please be really specific when giving arguments to back a new syscall > decision. Isn't "syscalls have completely independent description" specific enough? We are talking about API here, not the implementation details whether secretmem supports large pages or not. The purpose of memfd_create() is to create a file-like access to memory. The purpose of memfd_secret() is to create a way to access memory hidden from the kernel. I don't think overloading memfd_create() with the secretmem flags because they happen to return a file descriptor will be better for users, but rather will be more confusing. -- Sincerely yours, Mike.
