Sean Christopherson <[email protected]> writes: > On Fri, Oct 24, 2025, Ackerley Tng wrote: >> Ackerley Tng <[email protected]> writes: >> >> > From: Sean Christopherson <[email protected]> >> > >> > Accept gmem_flags in vm_mem_add() to be able to create a guest_memfd within >> > vm_mem_add(). >> > >> > When vm_mem_add() is used to set up a guest_memfd for a memslot, set up the >> > provided (or created) gmem_fd as the fd for the user memory region. This >> > makes it available to be mmap()-ed from just like fds from other memory >> > sources. mmap() from guest_memfd using the provided gmem_flags and >> > gmem_offset. >> > >> > Add a kvm_slot_to_fd() helper to provide convenient access to the file >> > descriptor of a memslot. >> > >> > Update existing callers of vm_mem_add() to pass 0 for gmem_flags to >> > preserve existing behavior. >> > >> > Signed-off-by: Sean Christopherson <[email protected]> >> > [For guest_memfds, mmap() using gmem_offset instead of 0 all the time.] >> > Signed-off-by: Ackerley Tng <[email protected]> >> > --- >> > tools/testing/selftests/kvm/include/kvm_util.h | 7 ++++++- >> > tools/testing/selftests/kvm/lib/kvm_util.c | 18 ++++++++++-------- >> > .../kvm/x86/private_mem_conversions_test.c | 2 +- >> > 3 files changed, 17 insertions(+), 10 deletions(-) >> > >> > >> > [...snip...] >> > >> > @@ -1050,13 +1049,16 @@ void vm_mem_add(struct kvm_vm *vm, enum >> > vm_mem_backing_src_type src_type, >> > } >> > >> > region->fd = -1; >> > - if (backing_src_is_shared(src_type)) >> > + if (flags & KVM_MEM_GUEST_MEMFD && gmem_flags & GUEST_MEMFD_FLAG_MMAP) >> > + region->fd = kvm_dup(gmem_fd); >> > + else if (backing_src_is_shared(src_type)) >> > region->fd = kvm_memfd_alloc(region->mmap_size, >> > src_type == >> > VM_MEM_SRC_SHARED_HUGETLB); >> > >> >> Doing this makes it hard to test the legacy dual-backing case. >> >> It actually broke x86/private_mem_conversions_test for the legacy >> dual-backing case because there's no way to mmap or provide a >> userspace_address from the memory provider that is not guest_memfd, as >> determined by src_type. > > Yes there is. This patch is a giant nop. The only thing that the core > library > doesn't support is mmap() on guest_memfd *and* the other src_type, and IMO > that > is big "don't care", because KVM doesn't even support that combination: > > if (kvm_gmem_supports_mmap(inode)) > slot->flags |= KVM_MEMSLOT_GMEM_ONLY; >
Makes sense. > I mean, we _could_ test that KVM ignores the hva for mapping, but that's a > different and unique test entirely. > > I did break x86/private_mem_conversions_test (I could have sworn I tested, > *sigh*), > but the bug is in: > > KVM: selftests: Provide function to look up guest_memfd details from gpa > > not here. And it's a trivial /facepalm-style fix: > > diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c > b/tools/testing/selftests/kvm/lib/kvm_util.c > index ee5b63f7cb50..23a8676fee6d 100644 > --- a/tools/testing/selftests/kvm/lib/kvm_util.c > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c > @@ -1680,7 +1680,7 @@ int kvm_gpa_to_guest_memfd(struct kvm_vm *vm, > vm_paddr_t gpa, off_t *fd_offset, > gpa_offset = gpa - region->region.guest_phys_addr; > *fd_offset = region->region.guest_memfd_offset + gpa_offset; > *nr_bytes = region->region.memory_size - gpa_offset; > - return region->fd; > + return region->region.guest_memfd; > } > > /* Create an interrupt controller chip for the specified VM. */ This works. Thanks!
