On Wed, Aug 27, 2025 at 07:36:46PM -0500, Ira Weiny wrote:
> 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().
>
> I like the fact this removes a poorly named function tdx_unpin() as well.
>
> That said, concerning gmem tracking page reference, I have some questions.
> In the TDX.PAGE.AUG path, [via kvm_gmem_get_pfn()] gmem takes a folio
kvm_mmu_finish_page_fault() will decrease the folio refcount.
> reference whereas the TDX.PAGE.ADD path [via kvm_gmem_populate()] does not
> take a folio reference.
>
> Why are these paths different?
>
> For this patch.
>
> Reviewed-by: Ira Weiny <ira.weiny@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
> >
>
>
