On Tue, Aug 26, 2025 at 05:05:15PM -0700, Sean Christopherson wrote: > Don't explicitly pin pages when mapping pages into the S-EPT, guest_memfd > doesn't support page migration in any capacity, i.e. there are no migrate > callbacks because guest_memfd pages *can't* be migrated. See the WARN in > kvm_gmem_migrate_folio(). Hmm, we implemented exactly the same patch at [1], where we explained the potential problems of not holding page refcount, and the explored various approaches, and related considerations. [1] https://lore.kernel.org/all/20250807094241.4523-1-yan.y.zhao@xxxxxxxxx/ > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > --- > arch/x86/kvm/vmx/tdx.c | 28 ++++------------------------ > 1 file changed, 4 insertions(+), 24 deletions(-) > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c > index 1724d82c8512..9fb6e5f02cc9 100644 > --- a/arch/x86/kvm/vmx/tdx.c > +++ b/arch/x86/kvm/vmx/tdx.c > @@ -1586,29 +1586,22 @@ void tdx_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa, int pgd_level) > td_vmcs_write64(to_tdx(vcpu), SHARED_EPT_POINTER, root_hpa); > } > > -static void tdx_unpin(struct kvm *kvm, struct page *page) > -{ > - put_page(page); > -} > - > static int tdx_mem_page_aug(struct kvm *kvm, gfn_t gfn, > - enum pg_level level, struct page *page) > + enum pg_level level, kvm_pfn_t pfn) > { > int tdx_level = pg_level_to_tdx_sept_level(level); > struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm); > + struct page *page = pfn_to_page(pfn); > gpa_t gpa = gfn_to_gpa(gfn); > u64 entry, level_state; > u64 err; > > err = tdh_mem_page_aug(&kvm_tdx->td, gpa, tdx_level, page, &entry, &level_state); > - if (unlikely(tdx_operand_busy(err))) { > - tdx_unpin(kvm, page); > + if (unlikely(tdx_operand_busy(err))) > return -EBUSY; > - } > > if (KVM_BUG_ON(err, kvm)) { > pr_tdx_error_2(TDH_MEM_PAGE_AUG, err, entry, level_state); > - tdx_unpin(kvm, page); > return -EIO; > } > > @@ -1642,29 +1635,18 @@ static int tdx_sept_set_private_spte(struct kvm *kvm, gfn_t gfn, > enum pg_level level, kvm_pfn_t pfn) > { > struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm); > - struct page *page = pfn_to_page(pfn); > > /* TODO: handle large pages. */ > if (KVM_BUG_ON(level != PG_LEVEL_4K, kvm)) > return -EINVAL; > > - /* > - * Because guest_memfd doesn't support page migration with > - * a_ops->migrate_folio (yet), no callback is triggered for KVM on page > - * migration. Until guest_memfd supports page migration, prevent page > - * migration. > - * TODO: Once guest_memfd introduces callback on page migration, > - * implement it and remove get_page/put_page(). > - */ > - get_page(page); > - > /* > * Read 'pre_fault_allowed' before 'kvm_tdx->state'; see matching > * barrier in tdx_td_finalize(). > */ > smp_rmb(); > if (likely(kvm_tdx->state == TD_STATE_RUNNABLE)) > - return tdx_mem_page_aug(kvm, gfn, level, page); > + return tdx_mem_page_aug(kvm, gfn, level, pfn); > > return tdx_mem_page_record_premap_cnt(kvm, gfn, level, pfn); > } > @@ -1715,7 +1697,6 @@ static int tdx_sept_drop_private_spte(struct kvm *kvm, gfn_t gfn, > return -EIO; > } > tdx_clear_page(page); > - tdx_unpin(kvm, page); > return 0; > } > > @@ -1795,7 +1776,6 @@ static int tdx_sept_zap_private_spte(struct kvm *kvm, gfn_t gfn, > if (tdx_is_sept_zap_err_due_to_premap(kvm_tdx, err, entry, level) && > !KVM_BUG_ON(!atomic64_read(&kvm_tdx->nr_premapped), kvm)) { > atomic64_dec(&kvm_tdx->nr_premapped); > - tdx_unpin(kvm, page); > return 0; > } > > -- > 2.51.0.268.g9569e192d0-goog >
