linux-kernel - [PATCH v3 5/8] KVM: x86/mmu: Add a field to control memslot rmap allocation

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Message-Id: <20210506184241.618958-6-bgardon@google.com>
Date:   Thu,  6 May 2021 11:42:38 -0700
From:   Ben Gardon <bgardon@...gle.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Kai Huang <kai.huang@...el.com>,
        Keqian Zhu <zhukeqian1@...wei.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH v3 5/8] KVM: x86/mmu: Add a field to control memslot rmap allocation

Add a field to control whether new memslots should have rmaps allocated
for them. As of this change, it's not safe to skip allocating rmaps, so
the field is always set to allocate rmaps. Future changes will make it
safe to operate without rmaps, using the TDP MMU. Then further changes
will allow the rmaps to be allocated lazily when needed for nested
oprtation.

No functional change expected.

Signed-off-by: Ben Gardon <bgardon@...gle.com>
---
 arch/x86/include/asm/kvm_host.h |  8 ++++++++
 arch/x86/kvm/mmu/mmu.c          |  2 ++
 arch/x86/kvm/x86.c              | 18 +++++++++++++-----
 3 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ad22d4839bcc..00065f9bbc5e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1122,6 +1122,12 @@ struct kvm_arch {
 	 */
 	spinlock_t tdp_mmu_pages_lock;
 #endif /* CONFIG_X86_64 */
+
+	/*
+	 * If set, rmaps have been allocated for all memslots and should be
+	 * allocated for any newly created or modified memslots.
+	 */
+	bool memslots_have_rmaps;
 };
 
 struct kvm_vm_stat {
@@ -1853,4 +1859,6 @@ static inline int kvm_cpu_get_apicid(int mps_cpu)
 
 int kvm_cpu_dirty_log_size(void);
 
+inline bool kvm_memslots_have_rmaps(struct kvm *kvm);
+
 #endif /* _ASM_X86_KVM_HOST_H */
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 930ac8a7e7c9..8761b4925755 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5469,6 +5469,8 @@ void kvm_mmu_init_vm(struct kvm *kvm)
 
 	kvm_mmu_init_tdp_mmu(kvm);
 
+	kvm->arch.memslots_have_rmaps = true;
+
 	node->track_write = kvm_mmu_pte_write;
 	node->track_flush_slot = kvm_mmu_invalidate_zap_pages_in_memslot;
 	kvm_page_track_register_notifier(kvm, node);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fc32a7dbe4c4..d7a40ce342cc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10868,7 +10868,13 @@ static int alloc_memslot_rmap(struct kvm_memory_slot *slot,
 	return -ENOMEM;
 }
 
-static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
+bool kvm_memslots_have_rmaps(struct kvm *kvm)
+{
+	return kvm->arch.memslots_have_rmaps;
+}
+
+static int kvm_alloc_memslot_metadata(struct kvm *kvm,
+				      struct kvm_memory_slot *slot,
 				      unsigned long npages)
 {
 	int i;
@@ -10881,9 +10887,11 @@ static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
 	 */
 	memset(&slot->arch, 0, sizeof(slot->arch));
 
-	r = alloc_memslot_rmap(slot, npages);
-	if (r)
-		return r;
+	if (kvm_memslots_have_rmaps(kvm)) {
+		r = alloc_memslot_rmap(slot, npages);
+		if (r)
+			return r;
+	}
 
 	for (i = 1; i < KVM_NR_PAGE_SIZES; ++i) {
 		struct kvm_lpage_info *linfo;
@@ -10954,7 +10962,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				enum kvm_mr_change change)
 {
 	if (change == KVM_MR_CREATE || change == KVM_MR_MOVE)
-		return kvm_alloc_memslot_metadata(memslot,
+		return kvm_alloc_memslot_metadata(kvm, memslot,
 						  mem->memory_size >> PAGE_SHIFT);
 	return 0;
 }
-- 
2.31.1.607.g51e8a6a459-goog