Hi Quentin, On Tue, 11 Feb 2025 at 16:57, Quentin Perret <qperret@xxxxxxxxxx> wrote: > > On Tuesday 11 Feb 2025 at 16:34:02 (+0000), Fuad Tabba wrote: > > > Sorry, yes, that wasn't clear. I meant that kvm_mem_is_private() calls > > > kvm_get_memory_attributes() which indexes kvm->mem_attr_array. The > > > comment in struct kvm indicates that this xarray is protected by RCU for > > > readers, so I was just checking if we were relying on > > > kvm_handle_guest_abort() to take srcu_read_lock(&kvm->srcu) for us, or > > > if there was something else more subtle here. > > > > I was kind of afraid that people would be confused by this, and I > > commented on it in the commit message of the earlier patch: > > https://lore.kernel.org/all/20250211121128.703390-6-tabba@xxxxxxxxxx/ > > > > > Note that the word "private" in the name of the function > > > kvm_mem_is_private() doesn't necessarily indicate that the memory > > > isn't shared, but is due to the history and evolution of > > > guest_memfd and the various names it has received. In effect, > > > this function is used to multiplex between the path of a normal > > > page fault and the path of a guest_memfd backed page fault. > > > > kvm_mem_is_private() is property of the memslot itself. No xarrays > > harmed in the process :) > > Ah, I see, but could someone enable CONFIG_GENERIC_PRIVATE_MEM and > related and get confused? Should KVM_GENERIC_MEMORY_ATTRIBUTES=n > depend on !ARM64? Or is it KVM_GMEM_SHARED_MEM that needs to depend on > the generic implementation being off? VMs that have sharing in place don't need KVM_GENERIC_MEMORY_ATTRIBUTES, since that presents the userspace view/desire of the state of the folio. It's not necessarily an arm64 thing, for example, CCA would need it, since it behaves like TDX. I guess that KVM_GMEM_SHARED_MEM and KVM_GENERIC_MEMORY_ATTRIBUTES are mutually exclusive. I cannot think how the two could be used or useful together. We could have a check to ensure that both are not enabled at the same time. The behavior in this patch series is that KVM_GMEM_SHARED_MEM selects GENERIC_PRIVATE_MEM. Also, to help reduce the confusion above, I could rename the variable is_private in user_mem_abort() to is_guestmem. WDYT? Cheers, /fuad > Thanks, > Quentin
