Re: [PATCH v10 02/41] KVM: guest_memfd: Introduce per-gmem attributes, use to guard user mappings

[Binbin Wu]

On 8/8/2026 5:52 AM, Ackerley Tng via B4 Relay wrote:
> From: Sean Christopherson <seanjc@xxxxxxxxxx>
> 
> Start plumbing in guest_memfd support for in-place private<=>shared
> conversions by tracking attributes via a maple tree.  KVM currently tracks
> private vs. shared attributes on a per-VM basis, which made sense when a
> guest_memfd _only_ supported private memory, but tracking per-VM simply
> can't work for in-place conversions as the shared/private status of a given
> page needs to be per-gmem_inode, not per-VM.
> 
> Use the filemap invalidation lock to protect the maple tree, as taking the
> lock for read when faulting in memory (for userspace or the guest) isn't
> expected to result in meaningful contention, and using a separate lock
> would add significant complexity (avoiding deadlock is quite difficult).
> 
> Co-developed-by: Vishal Annapurve <vannapurve@xxxxxxxxxx>
> Signed-off-by: Vishal Annapurve <vannapurve@xxxxxxxxxx>
> Co-developed-by: Fuad Tabba <tabba@xxxxxxxxxx>
> Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Tested-by: Shivank Garg <shivankg@xxxxxxx>
> Reviewed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> Co-developed-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>

With Sean's fixup in https://lore.kernel.org/kvm/annqex-kBOc0UJvp@xxxxxxxxxx/ 

Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>