Michael Roth <[email protected]> writes: > On Wed, Apr 01, 2026 at 07:05:16AM -0700, Ackerley Tng wrote: >> Ackerley Tng <[email protected]> writes: >> >> > All-shared guest_memfd used to be only supported for non-CoCo VMs where >> > preparation doesn't apply. INIT_SHARED is about to be supported for >> > non-CoCo VMs in a later patch in this series. >> > >> > In addition, KVM_SET_MEMORY_ATTRIBUTES2 is about to be supported in >> > guest_memfd in a later patch in this series. >> > >> > This means that the kvm fault handler may now call kvm_gmem_get_pfn() on a >> > shared folio for a CoCo VM where preparation applies. >> > >> > Add a check to make sure that preparation is only performed for private >> > folios. >> > >> > Preparation will be undone on freeing (see kvm_gmem_free_folio()) and on >> > conversion to shared. >> > >> > Signed-off-by: Ackerley Tng <[email protected]> >> > --- >> > virt/kvm/guest_memfd.c | 9 ++++++--- >> > 1 file changed, 6 insertions(+), 3 deletions(-) >> > >> > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c >> > index b6ffa8734175d..d414ebfcb4c19 100644 >> > --- a/virt/kvm/guest_memfd.c >> > +++ b/virt/kvm/guest_memfd.c >> > @@ -900,6 +900,7 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct >> > kvm_memory_slot *slot, >> > int *max_order) >> > { >> > pgoff_t index = kvm_gmem_get_index(slot, gfn); >> > + struct inode *inode; >> > struct folio *folio; >> > int r = 0; >> > >> > @@ -907,7 +908,8 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct >> > kvm_memory_slot *slot, >> > if (!file) >> > return -EFAULT; >> > >> > - filemap_invalidate_lock_shared(file_inode(file)->i_mapping); >> > + inode = file_inode(file); >> > + filemap_invalidate_lock_shared(inode->i_mapping); >> > >> > folio = __kvm_gmem_get_pfn(file, slot, index, pfn, max_order); >> > if (IS_ERR(folio)) { >> > @@ -920,7 +922,8 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct >> > kvm_memory_slot *slot, >> > folio_mark_uptodate(folio); >> > } >> > >> > - r = kvm_gmem_prepare_folio(kvm, slot, gfn, folio); >> > + if (kvm_gmem_is_private_mem(inode, index)) >> > + r = kvm_gmem_prepare_folio(kvm, slot, gfn, folio); >> >> Michael, I might have misunderstood you at the last guest_memfd call: >> sev_gmem_prepare() doesn't prepare a page for being a shared page, >> right? Does this work? That prepare is only called to "make private"? > > Hmm, I guess your guest_memfd-inplace-conversion-v4 branch is out of sync with > these patches? >
My bad, it was. I just force-pushed to github to synchronize them with this patch series. > I have the below local patch based on top of that for SNP-specific enablement, > which is basically identically, so suffice to say: yes, this should work > for SNP :) If any architecture pops up that needs to do some prep in > advance of mapping shared pages, then we could potentially plumb the > shared/private flag through to the arch-specific prep hook, as was also > suggested on the call, but it doesn't seem like that's needed by any > users for now. > Thanks for checking :) > -Mike > > Author: Michael Roth <[email protected]> > Date: Mon Oct 27 07:58:32 2025 -0500 > > KVM: guest_memfd: Don't prepare shared folios > > In the current guest_memfd logic, "preparation" is only used currently > to describe the additional work of putting a guest_memfd page into an > architecturally-defined "private" state, such as updating RMP table > entries for SEV-SNP guests. As such, there's no input to the > corresponding kvm_arch_gmem_prepare() hooks as to whether a page is > being prepared/accessed as shared or as private, so "preparation" will > end up being erroneously done on pages that were supposed to remain in a > shared state. Rather than plumb through the additional information > needed to distinguish between shared vs. private preparation, just > continue to only do preparation on private pages, as was the case prior > to support for GUEST_MEMFD_FLAG_MMAP being introduced. > > Signed-off-by: Michael Roth <[email protected]> > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 3acc6d983449..4869e59e4fc5 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -1249,7 +1249,8 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct > kvm_memory_slot *slot, > folio_mark_uptodate(folio); > } > > - r = kvm_gmem_prepare_folio(kvm, slot, gfn, folio); > + if (!kvm_gmem_is_shared_mem(file_inode(file), index)) > + r = kvm_gmem_prepare_folio(kvm, slot, gfn, folio); > > folio_unlock(folio); > >> >> > >> > folio_unlock(folio); >> > >> > @@ -930,7 +933,7 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct >> > kvm_memory_slot *slot, >> > folio_put(folio); >> > >> > out: >> > - filemap_invalidate_unlock_shared(file_inode(file)->i_mapping); >> > + filemap_invalidate_unlock_shared(inode->i_mapping); >> > return r; >> > } >> > EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_gmem_get_pfn); >> > >> > -- >> > 2.53.0.1018.g2bb0e51243-goog
