[RFC PATCH 05/12] KVM: TDX: Drop superfluous page pinning in S-EPT management

[Sean Christopherson <seanjc@google.com>]

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().

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 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