On Thu, 17 Jul 2025 17:27:28 +0100, Fuad Tabba <tabba@xxxxxxxxxx> wrote: > > Enable host userspace mmap support for guest_memfd-backed memory on > arm64. This change provides arm64 with the capability to map guest > memory at the host directly from guest_memfd: > > * Define kvm_arch_supports_gmem_mmap() for arm64: The > kvm_arch_supports_gmem_mmap() macro is defined for arm64 to be true if > CONFIG_KVM_GMEM_SUPPORTS_MMAP is enabled. For existing arm64 KVM VM > types that support guest_memfd, this enables them to use guest_memfd > with host userspace mappings. This provides a consistent behavior as > there are currently no arm64 CoCo VMs that rely on guest_memfd solely > for private, non-mappable memory. Future arm64 VM types can override > or restrict this behavior via the kvm_arch_supports_gmem_mmap() hook > if needed. > > * Select CONFIG_KVM_GMEM_SUPPORTS_MMAP in arm64 Kconfig. > > * Enforce KVM_MEMSLOT_GMEM_ONLY for guest_memfd on arm64: Checks are > added to ensure that if guest_memfd is enabled on arm64, > KVM_GMEM_SUPPORTS_MMAP must also be enabled. This means > guest_memfd-backed memory slots on arm64 are currently only supported > if they are intended for shared memory use cases (i.e., > kvm_memslot_is_gmem_only() is true). This design reflects the current > arm64 KVM ecosystem where guest_memfd is primarily being introduced > for VMs that support shared memory. > > Reviewed-by: James Houghton <jthoughton@xxxxxxxxxx> > Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx> > Acked-by: David Hildenbrand <david@xxxxxxxxxx> > Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx> > --- > arch/arm64/include/asm/kvm_host.h | 4 ++++ > arch/arm64/kvm/Kconfig | 2 ++ > arch/arm64/kvm/mmu.c | 7 +++++++ > 3 files changed, 13 insertions(+) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index 3e41a880b062..63f7827cfa1b 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -1674,5 +1674,9 @@ void compute_fgu(struct kvm *kvm, enum fgt_group_id fgt); > void get_reg_fixed_bits(struct kvm *kvm, enum vcpu_sysreg reg, u64 *res0, u64 *res1); > void check_feature_map(void); > > +#ifdef CONFIG_KVM_GMEM > +#define kvm_arch_supports_gmem(kvm) true > +#define kvm_arch_supports_gmem_mmap(kvm) IS_ENABLED(CONFIG_KVM_GMEM_SUPPORTS_MMAP) > +#endif nit: these two lines should be trivially 'true', and the #ifdef-ery removed, since both KVM_GMEM and KVM_GMEM_SUPPORTS_MMAP are always selected, no ifs, no buts. > > #endif /* __ARM64_KVM_HOST_H__ */ > diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig > index 713248f240e0..323b46b7c82f 100644 > --- a/arch/arm64/kvm/Kconfig > +++ b/arch/arm64/kvm/Kconfig > @@ -37,6 +37,8 @@ menuconfig KVM > select HAVE_KVM_VCPU_RUN_PID_CHANGE > select SCHED_INFO > select GUEST_PERF_EVENTS if PERF_EVENTS > + select KVM_GMEM > + select KVM_GMEM_SUPPORTS_MMAP > help > Support hosting virtualized guest machines. > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 8c82df80a835..85559b8a0845 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -2276,6 +2276,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, > if ((new->base_gfn + new->npages) > (kvm_phys_size(&kvm->arch.mmu) >> PAGE_SHIFT)) > return -EFAULT; > > + /* > + * Only support guest_memfd backed memslots with mappable memory, since > + * there aren't any CoCo VMs that support only private memory on arm64. > + */ > + if (kvm_slot_has_gmem(new) && !kvm_memslot_is_gmem_only(new)) > + return -EINVAL; > + > hva = new->userspace_addr; > reg_end = hva + (new->npages << PAGE_SHIFT); > Otherwise, Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx> M. -- Jazz isn't dead. It just smells funny.
