Re: [PATCH v4 00/12] KVM: mm: fd-based approach for supporting KVM guest private memory

[Chao Peng]

On Tue, Feb 08, 2022 at 08:33:18PM +0200, Mike Rapoport wrote:
> (addded linux-api)
> 
> On Tue, Jan 18, 2022 at 09:21:09PM +0800, Chao Peng wrote:
> > This is the v4 of this series which try to implement the fd-based KVM
> > guest private memory. The patches are based on latest kvm/queue branch
> > commit:
> > 
> >   fea31d169094 KVM: x86/pmu: Fix available_event_types check for
> >                REF_CPU_CYCLES event
> > 
> > Introduction
> > ------------
> > In general this patch series introduce fd-based memslot which provides
> > guest memory through memory file descriptor fd[offset,size] instead of
> > hva/size. The fd can be created from a supported memory filesystem
> > like tmpfs/hugetlbfs etc. which we refer as memory backing store. KVM
> > and the the memory backing store exchange callbacks when such memslot
> > gets created. At runtime KVM will call into callbacks provided by the
> > backing store to get the pfn with the fd+offset. Memory backing store
> > will also call into KVM callbacks when userspace fallocate/punch hole
> > on the fd to notify KVM to map/unmap secondary MMU page tables.
> > 
> > Comparing to existing hva-based memslot, this new type of memslot allows
> > guest memory unmapped from host userspace like QEMU and even the kernel
> > itself, therefore reduce attack surface and prevent bugs.
> > 
> > Based on this fd-based memslot, we can build guest private memory that
> > is going to be used in confidential computing environments such as Intel
> > TDX and AMD SEV. When supported, the memory backing store can provide
> > more enforcement on the fd and KVM can use a single memslot to hold both
> > the private and shared part of the guest memory. 
> > 
> > mm extension
> > ---------------------
> > Introduces new F_SEAL_INACCESSIBLE for shmem and new MFD_INACCESSIBLE
> > flag for memfd_create(), the file created with these flags cannot read(),
> > write() or mmap() etc via normal MMU operations. The file content can
> > only be used with the newly introduced memfile_notifier extension.
> 
> It would be great to see man page draft for new ABI flags

Yes I can provide the man page.

Thanks,
Chao