linux-kernel - [PATCHv2 09/12] KVM: TDX: Reclaim PAMT memory

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Message-ID: <20250609191340.2051741-10-kirill.shutemov@linux.intel.com>
Date: Mon,  9 Jun 2025 22:13:37 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com,
	dave.hansen@...ux.intel.com
Cc: rick.p.edgecombe@...el.com,
	isaku.yamahata@...el.com,
	kai.huang@...el.com,
	yan.y.zhao@...el.com,
	chao.gao@...el.com,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	kvm@...r.kernel.org,
	x86@...nel.org,
	linux-coco@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCHv2 09/12] KVM: TDX: Reclaim PAMT memory

The PAMT memory holds metadata for TDX-protected memory. With Dynamic
PAMT, PAMT_4K is allocated on demand. The kernel supplies the TDX module
with a few pages that cover 2M of host physical memory.

PAMT memory can be reclaimed when the last user is gone. It can happen
in a few code paths:

- On TDH.PHYMEM.PAGE.RECLAIM in tdx_reclaim_td_control_pages() and
  tdx_reclaim_page().

- On TDH.MEM.PAGE.REMOVE in tdx_sept_drop_private_spte().

- In tdx_sept_zap_private_spte() for pages that were in the queue to be
  added with TDH.MEM.PAGE.ADD, but it never happened due to an error.

- In tdx_sept_free_private_spt() for SEPT pages;

Add tdx_pamt_put() for memory that comes from guest_memfd and use
tdx_free_page() for the rest.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 arch/x86/kvm/vmx/tdx.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index bc9bc393f866..0aed7e73cd6b 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -353,7 +353,7 @@ static void tdx_reclaim_control_page(struct page *ctrl_page)
 	if (tdx_reclaim_page(ctrl_page))
 		return;
 
-	__free_page(ctrl_page);
+	tdx_free_page(ctrl_page);
 }
 
 struct tdx_flush_vp_arg {
@@ -584,7 +584,7 @@ static void tdx_reclaim_td_control_pages(struct kvm *kvm)
 	}
 	tdx_clear_page(kvm_tdx->td.tdr_page);
 
-	__free_page(kvm_tdx->td.tdr_page);
+	tdx_free_page(kvm_tdx->td.tdr_page);
 	kvm_tdx->td.tdr_page = NULL;
 }
 
@@ -1635,6 +1635,7 @@ static int tdx_sept_drop_private_spte(struct kvm *kvm, gfn_t gfn,
 		return -EIO;
 	}
 	tdx_clear_page(page);
+	tdx_pamt_put(page, level);
 	tdx_unpin(kvm, page);
 	return 0;
 }
@@ -1724,6 +1725,7 @@ 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_pamt_put(page, level);
 		tdx_unpin(kvm, page);
 		return 0;
 	}
@@ -1788,6 +1790,8 @@ int tdx_sept_free_private_spt(struct kvm *kvm, gfn_t gfn,
 			      enum pg_level level, void *private_spt)
 {
 	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
+	struct page *page = virt_to_page(private_spt);
+	int ret;
 
 	/*
 	 * free_external_spt() is only called after hkid is freed when TD is
@@ -1804,7 +1808,12 @@ int tdx_sept_free_private_spt(struct kvm *kvm, gfn_t gfn,
 	 * The HKID assigned to this TD was already freed and cache was
 	 * already flushed. We don't have to flush again.
 	 */
-	return tdx_reclaim_page(virt_to_page(private_spt));
+	ret = tdx_reclaim_page(virt_to_page(private_spt));
+	if (ret)
+		return ret;
+
+	tdx_pamt_put(page, PG_LEVEL_4K);
+	return 0;
 }
 
 int tdx_sept_remove_private_spte(struct kvm *kvm, gfn_t gfn,
-- 
2.47.2