On Wed, Apr 23, 2025 at 8:07 PM Yan Zhao <yan.y.zhao@xxxxxxxxx> wrote:
>
> Increase folio ref count before mapping a private page, and decrease
> folio ref count after a mapping failure or successfully removing a private
> page.
>
> The folio ref count to inc/dec corresponds to the mapping/unmapping level,
> ensuring the folio ref count remains balanced after entry splitting or
> merging.
>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
> ---
> arch/x86/kvm/vmx/tdx.c | 19 ++++++++++---------
> 1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 355b21fc169f..e23dce59fc72 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1501,9 +1501,9 @@ 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)
> +static void tdx_unpin(struct kvm *kvm, struct page *page, int level)
> {
> - put_page(page);
> + folio_put_refs(page_folio(page), KVM_PAGES_PER_HPAGE(level));
> }
>
> static int tdx_mem_page_aug(struct kvm *kvm, gfn_t gfn,
> @@ -1517,13 +1517,13 @@ static int tdx_mem_page_aug(struct kvm *kvm, gfn_t gfn,
>
> 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);
> + tdx_unpin(kvm, page, level);
> return -EBUSY;
> }
>
> if (KVM_BUG_ON(err, kvm)) {
> pr_tdx_error_2(TDH_MEM_PAGE_AUG, err, entry, level_state);
> - tdx_unpin(kvm, page);
> + tdx_unpin(kvm, page, level);
> return -EIO;
> }
>
> @@ -1570,10 +1570,11 @@ int tdx_sept_set_private_spte(struct kvm *kvm, gfn_t gfn,
> * 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().
> + * TODO: To support in-place-conversion in gmem in futre, remove
> + * folio_ref_add()/folio_put_refs().
With necessary infrastructure in guest_memfd [1] to prevent page
migration, is it necessary to acquire extra folio refcounts? If not,
why not just cleanup this logic now?
[1] https://git.kernel.org/pub/scm/virt/kvm/kvm.git/tree/virt/kvm/guest_memfd.c?h=kvm-coco-queue#n441
> Only increase the folio ref count
> + * when there're errors during removing private pages.
> */
> - get_page(page);
> + folio_ref_add(page_folio(page), KVM_PAGES_PER_HPAGE(level));
>
> /*
> * Read 'pre_fault_allowed' before 'kvm_tdx->state'; see matching
> @@ -1647,7 +1648,7 @@ static int tdx_sept_drop_private_spte(struct kvm *kvm, gfn_t gfn,
> return -EIO;
>
> tdx_clear_page(page, level);
> - tdx_unpin(kvm, page);
> + tdx_unpin(kvm, page, level);
> return 0;
> }
>
> @@ -1727,7 +1728,7 @@ 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);
> + tdx_unpin(kvm, page, level);
> return 0;
> }
>
> --
> 2.43.2
>
