[RFC 3/9] Introduce page table remove function for direct build EPT feature

[Yulei Zhang]

From: Yulei Zhang <yuleixzhang@xxxxxxxxxxx>

During guest boots up it will modify the memory slots multiple times,
so add page table remove function to free pre-pinned memory according
to the the memory slot changes.

Signed-off-by: Yulei Zhang <yuleixzhang@xxxxxxxxxxx>
---
 arch/x86/kvm/mmu/mmu.c | 56 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 1609012be67d..539974183653 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -6454,6 +6454,62 @@ int kvm_direct_tdp_populate_page_table(struct kvm *kvm, struct kvm_memory_slot *
 	return 0;
 }
 
+static int __kvm_remove_spte(struct kvm *kvm, u64 *addr, gfn_t gfn, int level)
+{
+	int i;
+	int ret = level;
+	bool present = false;
+	kvm_pfn_t pfn;
+	u64 *sptep = (u64 *)__va((*addr) & PT64_BASE_ADDR_MASK);
+	unsigned index = SHADOW_PT_INDEX(gfn << PAGE_SHIFT, level);
+
+	for (i = 0; i < PT64_ENT_PER_PAGE; ++i) {
+		if (is_shadow_present_pte(sptep[i])) {
+			if (i == index) {
+				if (!is_last_spte(sptep[i], level)) {
+					ret = __kvm_remove_spte(kvm, &sptep[i], gfn, level - 1);
+					if (is_shadow_present_pte(sptep[i]))
+						return ret;
+				} else {
+					pfn = spte_to_pfn(sptep[i]);
+					mmu_spte_clear_track_bits(&sptep[i]);
+					kvm_release_pfn_clean(pfn);
+					if (present)
+						return ret;
+				}
+			} else {
+				if (i > index)
+					return ret;
+				else
+					present = true;
+			}
+		}
+	}
+
+	if (!present) {
+		pfn = spte_to_pfn(*addr);
+		mmu_spte_clear_track_bits(addr);
+		kvm_release_pfn_clean(pfn);
+	}
+	return ret;
+}
+
+void kvm_direct_tdp_remove_page_table(struct kvm *kvm, struct kvm_memory_slot *slot)
+{
+	gfn_t gfn = slot->base_gfn;
+	int host_level;
+
+	if (!kvm->arch.global_root_hpa)
+		return;
+
+	for (gfn = slot->base_gfn;
+		gfn < slot->base_gfn + slot->npages;
+		gfn += KVM_PAGES_PER_HPAGE(host_level))
+		host_level = __kvm_remove_spte(kvm, &(kvm->arch.global_root_hpa), gfn, PT64_ROOT_4LEVEL);
+
+	kvm_flush_remote_tlbs(kvm);
+}
+
 /*
  * Calculate mmu pages needed for kvm.
  */
-- 
2.17.1