Commit 576d035e authored by Fuad Tabba's avatar Fuad Tabba Committed by Paolo Bonzini
Browse files

KVM: guest_memfd: Track guest_memfd mmap support in memslot 



Add a new internal flag, KVM_MEMSLOT_GMEM_ONLY, to the top half of
memslot->flags (which makes it strictly for KVM's internal use). This
flag tracks when a guest_memfd-backed memory slot supports host
userspace mmap operations, which implies that all memory, not just
private memory for CoCo VMs, is consumed through guest_memfd: "gmem
only".

This optimization avoids repeatedly checking the underlying guest_memfd
file for mmap support, which would otherwise require taking and
releasing a reference on the file for each check. By caching this
information directly in the memslot, we reduce overhead and simplify the
logic involved in handling guest_memfd-backed pages for host mappings.

Reviewed-by: default avatarGavin Shan <gshan@redhat.com>
Reviewed-by: default avatarShivank Garg <shivankg@amd.com>
Reviewed-by: default avatarXiaoyao Li <xiaoyao.li@intel.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Suggested-by: default avatarDavid Hildenbrand <david@redhat.com>
Signed-off-by: default avatarFuad Tabba <tabba@google.com>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-ID: <20250729225455.670324-12-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent a12578e1

include/linux/kvm_host.h

+10 −1
Original line number Diff line number Diff line
@@ -55,6 +55,7 @@ 
 * include/uapi/linux/kvm.h.

 */

#define KVM_MEMSLOT_INVALID			(1UL << 16)

#define KVM_MEMSLOT_GMEM_ONLY			(1UL << 17)



/*

 * Bit 63 of the memslot generation number is an "update in-progress flag",
@@ -2490,6 +2491,14 @@ static inline void kvm_prepare_memory_fault_exit(struct kvm_vcpu *vcpu, 
		vcpu->run->memory_fault.flags |= KVM_MEMORY_EXIT_FLAG_PRIVATE;

}



static inline bool kvm_memslot_is_gmem_only(const struct kvm_memory_slot *slot)

{

	if (!IS_ENABLED(CONFIG_KVM_GUEST_MEMFD))

		return false;



	return slot->flags & KVM_MEMSLOT_GMEM_ONLY;

}



#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES

static inline unsigned long kvm_get_memory_attributes(struct kvm *kvm, gfn_t gfn)

{

virt/kvm/guest_memfd.c

+2 −0
Original line number Diff line number Diff line
@@ -578,6 +578,8 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot, 
	 */

	WRITE_ONCE(slot->gmem.file, file);

	slot->gmem.pgoff = start;

	if (kvm_gmem_supports_mmap(inode))

		slot->flags |= KVM_MEMSLOT_GMEM_ONLY;



	xa_store_range(&gmem->bindings, start, end - 1, slot, GFP_KERNEL);

	filemap_invalidate_unlock(inode->i_mapping);