[PATCH v4 05/17] KVM: x86/tdp_mmu: Alloc external_spt page for mirror page table splitting

[Yan Zhao <yan.y.zhao@intel.com>]

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

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

When the mirror page table is split in tdp_mmu_split_huge_page(), the
corresponding external page table also needs to be split. Therefore,
allocate external_spt in tdp_mmu_alloc_sp_for_split() to prepare for the
splitting.

The external_spt will be gifted to the TDX module and mapped as a page
table page in the S-EPT during splitting. Since the TDX module will
initialize the page content in the DEMOTE SEAMCALL, there is no need to
zero external_spt.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
[sean: use __get_free_page(), let is_mirror_root be const and called once]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Co-developed-by: Yan Zhao <yan.y.zhao@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
---
v4:
- "bool mirror" --> "bool is_mirror_sp". (Sean)
- Use __get_free_page() instead of get_zeroed_page(). (Sean)
- let is_mirror_root be const and called once. (Sean)

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 | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 001449142d32..f3311317a63a 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1466,7 +1466,7 @@ 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 is_mirror_sp)
 {
 	struct kvm_mmu_page *sp;
 
@@ -1480,6 +1480,15 @@ static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(void)
 		return NULL;
 	}
 
+	if (is_mirror_sp) {
+		sp->external_spt = (void *)__get_free_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;
 }
 
@@ -1527,6 +1536,7 @@ static int tdp_mmu_split_huge_pages_root(struct kvm *kvm,
 					 gfn_t start, gfn_t end,
 					 int target_level, bool shared)
 {
+	const bool is_mirror_root = is_mirror_sp(root);
 	struct kvm_mmu_page *sp = NULL;
 	struct tdp_iter iter;
 
@@ -1559,7 +1569,7 @@ 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_root);
 
 			if (shared)
 				read_lock(&kvm->mmu_lock);
-- 
2.43.2