Apologies for the delayed response, and thank you for the review. On Fri, 26 Jun 2026 14:45:45 +0000, Brendan Jackman wrote: > On Tue Apr 21, 2026 at 4:55 PM UTC, Marc Zyngier wrote: > > Support for GUEST_MEMFD_FLAG_NO_DIRECT_MAP on arm64 depends on 1) direct > > map manipulations at 4k granularity being possible, and 2) FEAT_S2FWB. > > > > Where is this 4kB requirement enforced? Or is it that you means > > "PAGE_SIZE"? > > Yeah I believe this means PAGE_SIZE and that it's effectively enforced > by checking can_set_direct_map() in > kvm_arch_gmem_supports_no_direct_map().
Yes, this should say PAGE_SIZE rather than 4k. If I understand the arm64 MM code correctly, can_set_direct_map() is the capability gate, but it does not require the linear map to be built with page-sized PTEs from boot. Without BBML2_NOABORT, force_pte_mapping() builds the linear map with PAGE_SIZE PTEs. With BBML2_NOABORT, update_range_prot() can use split_kernel_leaf_mapping() to safely split larger mappings on demand before changing a PAGE_SIZE range. I'll update the v13 commit message to describe this. On Tue, 21 Apr 2026 17:55:05 +0100, Marc Zyngier wrote: > KVM/arm64 has: > > select KVM_GUEST_MEMFD I also confirmed that KVM/arm64 selects KVM_GUEST_MEMFD, so I'll drop the redundant #ifdef in v13. > Why is it an inline function? Given that it takes a kvm parameter, > I fully expect that you'll have to evaluate this at some point. > > But since struct kvm cannot be dereferenced in asm/kvm_host.h, it will > have to move. How about doing it right now? Agreed. Although the current implementation does not dereference kvm, it makes sense to move it out of asm/kvm_host.h now. I'll move the implementation to an arm64 KVM .c file in v13.
