linux-kernel - [RFC, PATCH 11/12] KVM: TDX: Reclaim PAMT memory

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Message-ID: <20250502130828.4071412-12-kirill.shutemov@linux.intel.com>
Date: Fri,  2 May 2025 16:08:27 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com
Cc: rick.p.edgecombe@...el.com,
	isaku.yamahata@...el.com,
	kai.huang@...el.com,
	yan.y.zhao@...el.com,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	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: [RFC, PATCH 11/12] 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.

Add tdx_pamt_put() in these code paths.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 arch/x86/kvm/vmx/tdx.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 0f06ae7ff6b9..352f7b41f611 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -487,8 +487,11 @@ static int tdx_reclaim_page(struct page *page)
 	int r;
 
 	r = __tdx_reclaim_page(page);
-	if (!r)
+	if (!r) {
 		tdx_clear_page(page);
+		tdx_pamt_put(page);
+	}
+
 	return r;
 }
 
@@ -737,6 +740,7 @@ static void tdx_reclaim_td_control_pages(struct kvm *kvm)
 		return;
 	}
 	tdx_clear_page(kvm_tdx->td.tdr_page);
+	tdx_pamt_put(kvm_tdx->td.tdr_page);
 
 	__free_page(kvm_tdx->td.tdr_page);
 	kvm_tdx->td.tdr_page = NULL;
@@ -1768,6 +1772,7 @@ static int tdx_sept_drop_private_spte(struct kvm *kvm, gfn_t gfn,
 		return -EIO;
 	}
 	tdx_clear_page(page);
+	tdx_pamt_put(page);
 	tdx_unpin(kvm, page);
 	return 0;
 }
@@ -1848,6 +1853,7 @@ 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);
 		tdx_unpin(kvm, page);
 		return 0;
 	}
-- 
2.47.2