[PATCH v16 11/17] RISC-V: KVM: Implement MMU notifiers

[Anup Patel <anup.patel@wdc.com>]

This patch implements MMU notifiers for KVM RISC-V so that Guest
physical address space is in-sync with Host physical address space.

This will allow swapping, page migration, etc to work transparently
with KVM RISC-V.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Alexander Graf <graf@amazon.com>
---
 arch/riscv/include/asm/kvm_host.h |   7 ++
 arch/riscv/kvm/Kconfig            |   1 +
 arch/riscv/kvm/mmu.c              | 144 +++++++++++++++++++++++++++++-
 arch/riscv/kvm/vm.c               |   1 +
 4 files changed, 149 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
index 5d70c8cf3733..d25f181c3433 100644
--- a/arch/riscv/include/asm/kvm_host.h
+++ b/arch/riscv/include/asm/kvm_host.h
@@ -203,6 +203,13 @@ static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
 static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
 static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}
 
+#define KVM_ARCH_WANT_MMU_NOTIFIER
+int kvm_unmap_hva_range(struct kvm *kvm, unsigned long start,
+			unsigned long end, unsigned int flags);
+int kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte);
+int kvm_age_hva(struct kvm *kvm, unsigned long start, unsigned long end);
+int kvm_test_age_hva(struct kvm *kvm, unsigned long hva);
+
 void __kvm_riscv_hfence_gvma_vmid_gpa(unsigned long gpa, unsigned long vmid);
 void __kvm_riscv_hfence_gvma_vmid(unsigned long vmid);
 void __kvm_riscv_hfence_gvma_gpa(unsigned long gpa);
diff --git a/arch/riscv/kvm/Kconfig b/arch/riscv/kvm/Kconfig
index 633063edaee8..a712bb910cda 100644
--- a/arch/riscv/kvm/Kconfig
+++ b/arch/riscv/kvm/Kconfig
@@ -20,6 +20,7 @@ if VIRTUALIZATION
 config KVM
 	tristate "Kernel-based Virtual Machine (KVM) support (EXPERIMENTAL)"
 	depends on RISCV_SBI && MMU
+	select MMU_NOTIFIER
 	select PREEMPT_NOTIFIERS
 	select ANON_INODES
 	select KVM_MMIO
diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
index e311c4bb0b8a..56fda9ef70fd 100644
--- a/arch/riscv/kvm/mmu.c
+++ b/arch/riscv/kvm/mmu.c
@@ -296,7 +296,8 @@ static void stage2_op_pte(struct kvm *kvm, gpa_t addr,
 	}
 }
 
-static void stage2_unmap_range(struct kvm *kvm, gpa_t start, gpa_t size)
+static void stage2_unmap_range(struct kvm *kvm, gpa_t start,
+			       gpa_t size, bool may_block)
 {
 	int ret;
 	pte_t *ptep;
@@ -321,6 +322,13 @@ static void stage2_unmap_range(struct kvm *kvm, gpa_t start, gpa_t size)
 
 next:
 		addr += page_size;
+
+		/*
+		 * If the range is too large, release the kvm->mmu_lock
+		 * to prevent starvation and lockup detector warnings.
+		 */
+		if (may_block && addr < end)
+			cond_resched_lock(&kvm->mmu_lock);
 	}
 }
 
@@ -404,6 +412,38 @@ int stage2_ioremap(struct kvm *kvm, gpa_t gpa, phys_addr_t hpa,
 
 }
 
+static int handle_hva_to_gpa(struct kvm *kvm,
+			     unsigned long start,
+			     unsigned long end,
+			     int (*handler)(struct kvm *kvm,
+					    gpa_t gpa, u64 size,
+					    void *data),
+			     void *data)
+{
+	struct kvm_memslots *slots;
+	struct kvm_memory_slot *memslot;
+	int ret = 0;
+
+	slots = kvm_memslots(kvm);
+
+	/* we only care about the pages that the guest sees */
+	kvm_for_each_memslot(memslot, slots) {
+		unsigned long hva_start, hva_end;
+		gfn_t gpa;
+
+		hva_start = max(start, memslot->userspace_addr);
+		hva_end = min(end, memslot->userspace_addr +
+					(memslot->npages << PAGE_SHIFT));
+		if (hva_start >= hva_end)
+			continue;
+
+		gpa = hva_to_gfn_memslot(hva_start, memslot) << PAGE_SHIFT;
+		ret |= handler(kvm, gpa, (u64)(hva_end - hva_start), data);
+	}
+
+	return ret;
+}
+
 void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
 					     struct kvm_memory_slot *slot,
 					     gfn_t gfn_offset,
@@ -549,7 +589,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	spin_lock(&kvm->mmu_lock);
 	if (ret)
 		stage2_unmap_range(kvm, mem->guest_phys_addr,
-				   mem->memory_size);
+				   mem->memory_size, false);
 	spin_unlock(&kvm->mmu_lock);
 
 out:
@@ -557,6 +597,96 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	return ret;
 }
 
+static int kvm_unmap_hva_handler(struct kvm *kvm,
+				 gpa_t gpa, u64 size, void *data)
+{
+	unsigned int flags = *(unsigned int *)data;
+	bool may_block = flags & MMU_NOTIFIER_RANGE_BLOCKABLE;
+
+	stage2_unmap_range(kvm, gpa, size, may_block);
+	return 0;
+}
+
+int kvm_unmap_hva_range(struct kvm *kvm, unsigned long start,
+			unsigned long end, unsigned int flags)
+{
+	if (!kvm->arch.pgd)
+		return 0;
+
+	handle_hva_to_gpa(kvm, start, end, &kvm_unmap_hva_handler, &flags);
+	return 0;
+}
+
+static int kvm_set_spte_handler(struct kvm *kvm,
+				gpa_t gpa, u64 size, void *data)
+{
+	pte_t *pte = (pte_t *)data;
+
+	WARN_ON(size != PAGE_SIZE);
+	stage2_set_pte(kvm, 0, NULL, gpa, pte);
+
+	return 0;
+}
+
+int kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte)
+{
+	unsigned long end = hva + PAGE_SIZE;
+	kvm_pfn_t pfn = pte_pfn(pte);
+	pte_t stage2_pte;
+
+	if (!kvm->arch.pgd)
+		return 0;
+
+	stage2_pte = pfn_pte(pfn, PAGE_WRITE_EXEC);
+	handle_hva_to_gpa(kvm, hva, end, &kvm_set_spte_handler, &stage2_pte);
+
+	return 0;
+}
+
+static int kvm_age_hva_handler(struct kvm *kvm,
+				gpa_t gpa, u64 size, void *data)
+{
+	pte_t *ptep;
+	u32 ptep_level = 0;
+
+	WARN_ON(size != PAGE_SIZE && size != PMD_SIZE && size != PGDIR_SIZE);
+
+	if (!stage2_get_leaf_entry(kvm, gpa, &ptep, &ptep_level))
+		return 0;
+
+	return ptep_test_and_clear_young(NULL, 0, ptep);
+}
+
+int kvm_age_hva(struct kvm *kvm, unsigned long start, unsigned long end)
+{
+	if (!kvm->arch.pgd)
+		return 0;
+
+	return handle_hva_to_gpa(kvm, start, end, kvm_age_hva_handler, NULL);
+}
+
+static int kvm_test_age_hva_handler(struct kvm *kvm,
+				    gpa_t gpa, u64 size, void *data)
+{
+	pte_t *ptep;
+	u32 ptep_level = 0;
+
+	WARN_ON(size != PAGE_SIZE && size != PMD_SIZE);
+	if (!stage2_get_leaf_entry(kvm, gpa, &ptep, &ptep_level))
+		return 0;
+
+	return pte_young(*ptep);
+}
+
+int kvm_test_age_hva(struct kvm *kvm, unsigned long hva)
+{
+	if (!kvm->arch.pgd)
+		return 0;
+
+	return handle_hva_to_gpa(kvm, hva, hva,
+				 kvm_test_age_hva_handler, NULL);
+}
+
 int kvm_riscv_stage2_map(struct kvm_vcpu *vcpu,
 			 struct kvm_memory_slot *memslot,
 			 gpa_t gpa, unsigned long hva, bool is_write)
@@ -571,7 +701,7 @@ int kvm_riscv_stage2_map(struct kvm_vcpu *vcpu,
 	struct kvm_mmu_page_cache *pcache = &vcpu->arch.mmu_page_cache;
 	bool logging = (memslot->dirty_bitmap &&
 			!(memslot->flags & KVM_MEM_READONLY)) ? true : false;
-	unsigned long vma_pagesize;
+	unsigned long vma_pagesize, mmu_seq;
 
 	mmap_read_lock(current->mm);
 
@@ -610,6 +740,8 @@ int kvm_riscv_stage2_map(struct kvm_vcpu *vcpu,
 		return ret;
 	}
 
+	mmu_seq = kvm->mmu_notifier_seq;
+
 	hfn = gfn_to_pfn_prot(kvm, gfn, is_write, &writeable);
 	if (hfn == KVM_PFN_ERR_HWPOISON) {
 		send_sig_mceerr(BUS_MCEERR_AR, (void __user *)hva,
@@ -628,6 +760,9 @@ int kvm_riscv_stage2_map(struct kvm_vcpu *vcpu,
 
 	spin_lock(&kvm->mmu_lock);
 
+	if (mmu_notifier_retry(kvm, mmu_seq))
+		goto out_unlock;
+
 	if (writeable) {
 		kvm_set_pfn_dirty(hfn);
 		mark_page_dirty(kvm, gfn);
@@ -641,6 +776,7 @@ int kvm_riscv_stage2_map(struct kvm_vcpu *vcpu,
 	if (ret)
 		kvm_err("Failed to map in stage2\n");
 
+out_unlock:
 	spin_unlock(&kvm->mmu_lock);
 	kvm_set_pfn_accessed(hfn);
 	kvm_release_pfn_clean(hfn);
@@ -677,7 +813,7 @@ void kvm_riscv_stage2_free_pgd(struct kvm *kvm)
 
 	spin_lock(&kvm->mmu_lock);
 	if (kvm->arch.pgd) {
-		stage2_unmap_range(kvm, 0UL, stage2_gpa_size);
+		stage2_unmap_range(kvm, 0UL, stage2_gpa_size, false);
 		pgd = READ_ONCE(kvm->arch.pgd);
 		kvm->arch.pgd = NULL;
 		kvm->arch.pgd_phys = 0;
diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
index 6cde69a82252..00a1a88008be 100644
--- a/arch/riscv/kvm/vm.c
+++ b/arch/riscv/kvm/vm.c
@@ -49,6 +49,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_IOEVENTFD:
 	case KVM_CAP_DEVICE_CTRL:
 	case KVM_CAP_USER_MEMORY:
+	case KVM_CAP_SYNC_MMU:
 	case KVM_CAP_DESTROY_MEMORY_REGION_WORKS:
 	case KVM_CAP_ONE_REG:
 	case KVM_CAP_READONLY_MEM:
-- 
2.25.1