linux-kernel - [PATCH v3 10/24] KVM: x86/tdp_mmu: Alloc external

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Message-ID: <20260106102122.25091-1-yan.y.zhao@intel.com>
Date: Tue,  6 Jan 2026 18:21:22 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com
Cc: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	x86@...nel.org,
	rick.p.edgecombe@...el.com,
	dave.hansen@...el.com,
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	isaku.yamahata@...el.com,
	xiaoyao.li@...el.com,
	kai.huang@...el.com,
	binbin.wu@...ux.intel.com,
	chao.p.peng@...el.com,
	chao.gao@...el.com,
	yan.y.zhao@...el.com
Subject: [PATCH v3 10/24] KVM: x86/tdp_mmu: Alloc external_spt page for mirror page table splitting

From: Isaku Yamahata <isaku.yamahata@...el.com>

Enhance tdp_mmu_alloc_sp_for_split() to allocate a page table page for the
external page table for splitting the mirror page table.

Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
Co-developed-by: Yan Zhao <yan.y.zhao@...el.com>
Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
---
v3:
- Removed unnecessary declaration of tdp_mmu_alloc_sp_for_split(). (Kai)
- Fixed a typo in the patch log. (Kai)

RFC v2:
- NO change.

RFC v1:
- Rebased and simplified the code.
---
 arch/x86/kvm/mmu/tdp_mmu.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 9b45ffb8585f..074209d91ec3 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1535,7 +1535,7 @@ bool kvm_tdp_mmu_wrprot_slot(struct kvm *kvm,
 	return spte_set;
 }
 
-static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(void)
+static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(bool mirror)
 {
 	struct kvm_mmu_page *sp;
 
@@ -1549,6 +1549,15 @@ static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(void)
 		return NULL;
 	}
 
+	if (mirror) {
+		sp->external_spt = (void *)get_zeroed_page(GFP_KERNEL_ACCOUNT);
+		if (!sp->external_spt) {
+			free_page((unsigned long)sp->spt);
+			kmem_cache_free(mmu_page_header_cache, sp);
+			return NULL;
+		}
+	}
+
 	return sp;
 }
 
@@ -1628,7 +1637,7 @@ static int tdp_mmu_split_huge_pages_root(struct kvm *kvm,
 			else
 				write_unlock(&kvm->mmu_lock);
 
-			sp = tdp_mmu_alloc_sp_for_split();
+			sp = tdp_mmu_alloc_sp_for_split(is_mirror_sp(root));
 
 			if (shared)
 				read_lock(&kvm->mmu_lock);
-- 
2.43.2