Re: [PATCH RFC 0/5] mm/gup: Introduce exclusive GUP pinning

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Thu, Jun 20, 2024 at 01:30:29PM -0700, Sean Christopherson wrote:
> I.e. except for blatant bugs, e.g. use-after-free, we need to be able to guarantee
> with 100% accuracy that there are no outstanding mappings when converting a page
> from shared=>private.  Crossing our fingers and hoping that short-term GUP will
> have gone away isn't enough.

To be clear it is not crossing fingers. If the page refcount is 0 then
there are no references to that memory anywhere at all. It is 100%
certain.

It may take time to reach zero, but when it does it is safe.

Many things rely on this property, including FSDAX.

> For non-CoCo VMs, I expect we'll want to be much more permissive, but I think
> they'll be a complete non-issue because there is no shared vs. private to worry
> about.  We can simply allow any and all userspace mappings for guest_memfd that is
> attached to a "regular" VM, because a misbehaving userspace only loses whatever
> hardening (or other benefits) was being provided by using guest_memfd.  I.e. the
> kernel and system at-large isn't at risk.

It does seem to me like guest_memfd should really focus on the private
aspect.

If we need normal memfd enhancements of some kind to work better with
KVM then that may be a better option than turning guest_memfd into
memfd.

Jason




[Index of Archives]     [Linux Wireless]     [Linux Kernel]     [ATH6KL]     [Linux Bluetooth]     [Linux Netdev]     [Kernel Newbies]     [Share Photos]     [IDE]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux ATA RAID]     [Samba]     [Device Mapper]

  Powered by Linux