diff mbox series

[v4,4/7] KVM: Move MMU lock acquisition for test/clear_young to architecture

Message ID 20240529180510.2295118-5-jthoughton@google.com (mailing list archive)
State New, archived
Headers show
Series mm: multi-gen LRU: Walk secondary MMU page tables while aging | expand

Commit Message

James Houghton May 29, 2024, 6:05 p.m. UTC 
For implementation mmu_notifier_{test,clear}_young, the KVM memslot
walker used to take the MMU lock for us. Now make the architectures
take it themselves.

Don't relax locking for any architecture except powerpc e500; its
implementations of kvm_age_gfn and kvm_test_age_gfn simply return false,
so there is no need to grab the KVM MMU lock.

Signed-off-by: James Houghton <jthoughton@google.com>
---
 arch/arm64/kvm/mmu.c      | 30 ++++++++++++++++++++++--------
 arch/loongarch/kvm/mmu.c  | 20 +++++++++++++++-----
 arch/mips/kvm/mmu.c       | 21 ++++++++++++++++-----
 arch/powerpc/kvm/book3s.c | 14 ++++++++++++--
 arch/riscv/kvm/mmu.c      | 26 ++++++++++++++++++++------
 arch/x86/kvm/mmu/mmu.c    |  8 ++++++++
 virt/kvm/kvm_main.c       |  4 ++--
 7 files changed, 95 insertions(+), 28 deletions(-)

Comments

Sean Christopherson May 29, 2024, 9:55 p.m. UTC | #1 
On Wed, May 29, 2024, James Houghton wrote:
> For implementation mmu_notifier_{test,clear}_young, the KVM memslot
> walker used to take the MMU lock for us. Now make the architectures
> take it themselves.

Hmm, *forcing* architectures to take mmu_lock is a step backwards.  Rather than
add all of this churn, what about adding CONFIG_KVM_MMU_NOTIFIER_LOCKLESS, e.g.

static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn,
							 unsigned long start,
							 unsigned long end,
							 gfn_handler_t handler)
{
	struct kvm *kvm = mmu_notifier_to_kvm(mn);
	const struct kvm_mmu_notifier_range range = {
		.start		= start,
		.end		= end,
		.handler	= handler,
		.on_lock	= (void *)kvm_null_fn,
		.flush_on_ret	= false,
		.may_block	= false,
		.lockless	= IS_ENABLED(CONFIG_KVM_MMU_NOTIFIER_LOCKLESS),
	};

	return __kvm_handle_hva_range(kvm, &range).ret;
}
James Houghton May 30, 2024, 3:27 a.m. UTC | #2 
On Wed, May 29, 2024 at 2:55 PM Sean Christopherson <seanjc@google.com> wrote:
>
> On Wed, May 29, 2024, James Houghton wrote:
> > For implementation mmu_notifier_{test,clear}_young, the KVM memslot
> > walker used to take the MMU lock for us. Now make the architectures
> > take it themselves.
>
> Hmm, *forcing* architectures to take mmu_lock is a step backwards.  Rather than
> add all of this churn, what about adding CONFIG_KVM_MMU_NOTIFIER_LOCKLESS, e.g.
>
> static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn,
>                                                          unsigned long start,
>                                                          unsigned long end,
>                                                          gfn_handler_t handler)
> {
>         struct kvm *kvm = mmu_notifier_to_kvm(mn);
>         const struct kvm_mmu_notifier_range range = {
>                 .start          = start,
>                 .end            = end,
>                 .handler        = handler,
>                 .on_lock        = (void *)kvm_null_fn,
>                 .flush_on_ret   = false,
>                 .may_block      = false,
>                 .lockless       = IS_ENABLED(CONFIG_KVM_MMU_NOTIFIER_LOCKLESS),
>         };
>
>         return __kvm_handle_hva_range(kvm, &range).ret;
> }

Thanks Sean, yes this is a lot better. I will do this for v5.
diff mbox series

Patch

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 8bcab0cc3fe9..8337009dde77 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1773,25 +1773,39 @@  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	u64 size = (range->end - range->start) << PAGE_SHIFT;
+	bool young = false;
+
+	write_lock(&kvm->mmu_lock);
 
 	if (!kvm->arch.mmu.pgt)
-		return false;
+		goto out;
 
-	return kvm_pgtable_stage2_test_clear_young(kvm->arch.mmu.pgt,
-						   range->start << PAGE_SHIFT,
-						   size, true);
+	young = kvm_pgtable_stage2_test_clear_young(kvm->arch.mmu.pgt,
+						    range->start << PAGE_SHIFT,
+						    size, true);
+
+out:
+	write_unlock(&kvm->mmu_lock);
+	return young;
 }
 
 bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	u64 size = (range->end - range->start) << PAGE_SHIFT;
+	bool young = false;
+
+	write_lock(&kvm->mmu_lock);
 
 	if (!kvm->arch.mmu.pgt)
-		return false;
+		goto out;
 
-	return kvm_pgtable_stage2_test_clear_young(kvm->arch.mmu.pgt,
-						   range->start << PAGE_SHIFT,
-						   size, false);
+	young = kvm_pgtable_stage2_test_clear_young(kvm->arch.mmu.pgt,
+						    range->start << PAGE_SHIFT,
+						    size, false);
+
+out:
+	write_unlock(&kvm->mmu_lock);
+	return young;
 }
 
 phys_addr_t kvm_mmu_get_httbr(void)
diff --git a/arch/loongarch/kvm/mmu.c b/arch/loongarch/kvm/mmu.c
index 98883aa23ab8..5eb262bcf6b0 100644
--- a/arch/loongarch/kvm/mmu.c
+++ b/arch/loongarch/kvm/mmu.c
@@ -497,24 +497,34 @@  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	kvm_ptw_ctx ctx;
+	bool young;
+
+	spin_lock(&kvm->mmu_lock);
 
 	ctx.flag = 0;
 	ctx.ops = kvm_mkold_pte;
 	kvm_ptw_prepare(kvm, &ctx);
 
-	return kvm_ptw_top(kvm->arch.pgd, range->start << PAGE_SHIFT,
+	young = kvm_ptw_top(kvm->arch.pgd, range->start << PAGE_SHIFT,
 				range->end << PAGE_SHIFT, &ctx);
+
+	spin_unlock(&kvm->mmu_lock);
+	return young;
 }
 
 bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	gpa_t gpa = range->start << PAGE_SHIFT;
-	kvm_pte_t *ptep = kvm_populate_gpa(kvm, NULL, gpa, 0);
+	kvm_pte_t *ptep;
+	bool young;
 
-	if (ptep && kvm_pte_present(NULL, ptep) && kvm_pte_young(*ptep))
-		return true;
+	spin_lock(&kvm->mmu_lock);
+	ptep = kvm_populate_gpa(kvm, NULL, gpa, 0);
 
-	return false;
+	young = ptep && kvm_pte_present(NULL, ptep) && kvm_pte_young(*ptep);
+
+	spin_unlock(&kvm->mmu_lock);
+	return young;
 }
 
 /*
diff --git a/arch/mips/kvm/mmu.c b/arch/mips/kvm/mmu.c
index c17157e700c0..db3b7cf22db1 100644
--- a/arch/mips/kvm/mmu.c
+++ b/arch/mips/kvm/mmu.c
@@ -446,17 +446,28 @@  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 
 bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
-	return kvm_mips_mkold_gpa_pt(kvm, range->start, range->end);
+	bool young;
+
+	spin_lock(&kvm->mmu_lock);
+	young = kvm_mips_mkold_gpa_pt(kvm, range->start, range->end);
+	spin_unlock(&kvm->mmu_lock);
+	return young;
 }
 
 bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	gpa_t gpa = range->start << PAGE_SHIFT;
-	pte_t *gpa_pte = kvm_mips_pte_for_gpa(kvm, NULL, gpa);
+	pte_t *gpa_pte;
+	bool young = false;
 
-	if (!gpa_pte)
-		return false;
-	return pte_young(*gpa_pte);
+	spin_lock(&kvm->mmu_lock);
+	gpa_pte = kvm_mips_pte_for_gpa(kvm, NULL, gpa);
+
+	if (gpa_pte)
+		young = pte_young(*gpa_pte);
+
+	spin_unlock(&kvm->mmu_lock);
+	return young;
 }
 
 /**
diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index ff6c38373957..f503ab9ac3a5 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -887,12 +887,22 @@  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 
 bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
-	return kvm->arch.kvm_ops->age_gfn(kvm, range);
+	bool young;
+
+	spin_lock(&kvm->mmu_lock);
+	young = kvm->arch.kvm_ops->age_gfn(kvm, range);
+	spin_unlock(&kvm->mmu_lock);
+	return young;
 }
 
 bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
-	return kvm->arch.kvm_ops->test_age_gfn(kvm, range);
+	bool young;
+
+	spin_lock(&kvm->mmu_lock);
+	young = kvm->arch.kvm_ops->test_age_gfn(kvm, range);
+	spin_unlock(&kvm->mmu_lock);
+	return young;
 }
 
 int kvmppc_core_init_vm(struct kvm *kvm)
diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
index b63650f9b966..c78abe8041fb 100644
--- a/arch/riscv/kvm/mmu.c
+++ b/arch/riscv/kvm/mmu.c
@@ -555,17 +555,24 @@  bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 	pte_t *ptep;
 	u32 ptep_level = 0;
 	u64 size = (range->end - range->start) << PAGE_SHIFT;
+	bool young = false;
+
+	spin_lock(&kvm->mmu_lock);
 
 	if (!kvm->arch.pgd)
-		return false;
+		goto out;
 
 	WARN_ON(size != PAGE_SIZE && size != PMD_SIZE && size != PUD_SIZE);
 
 	if (!gstage_get_leaf_entry(kvm, range->start << PAGE_SHIFT,
 				   &ptep, &ptep_level))
-		return false;
+		goto out;
+
+	young = ptep_test_and_clear_young(NULL, 0, ptep);
 
-	return ptep_test_and_clear_young(NULL, 0, ptep);
+out:
+	spin_unlock(&kvm->mmu_lock);
+	return young;
 }
 
 bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
@@ -573,17 +580,24 @@  bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 	pte_t *ptep;
 	u32 ptep_level = 0;
 	u64 size = (range->end - range->start) << PAGE_SHIFT;
+	bool young = false;
+
+	spin_lock(&kvm->mmu_lock);
 
 	if (!kvm->arch.pgd)
-		return false;
+		goto out;
 
 	WARN_ON(size != PAGE_SIZE && size != PMD_SIZE && size != PUD_SIZE);
 
 	if (!gstage_get_leaf_entry(kvm, range->start << PAGE_SHIFT,
 				   &ptep, &ptep_level))
-		return false;
+		goto out;
+
+	young = pte_young(ptep_get(ptep));
 
-	return pte_young(ptep_get(ptep));
+out:
+	spin_unlock(&kvm->mmu_lock);
+	return young;
 }
 
 int kvm_riscv_gstage_map(struct kvm_vcpu *vcpu,
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 662f62dfb2aa..6a2a557c2c31 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1630,12 +1630,16 @@  bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	bool young = false;
 
+	write_lock(&kvm->mmu_lock);
+
 	if (kvm_memslots_have_rmaps(kvm))
 		young = kvm_handle_gfn_range(kvm, range, kvm_age_rmap);
 
 	if (tdp_mmu_enabled)
 		young |= kvm_tdp_mmu_age_gfn_range(kvm, range);
 
+	write_unlock(&kvm->mmu_lock);
+
 	return young;
 }
 
@@ -1643,12 +1647,16 @@  bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	bool young = false;
 
+	write_lock(&kvm->mmu_lock);
+
 	if (kvm_memslots_have_rmaps(kvm))
 		young = kvm_handle_gfn_range(kvm, range, kvm_test_age_rmap);
 
 	if (tdp_mmu_enabled)
 		young |= kvm_tdp_mmu_test_age_gfn(kvm, range);
 
+	write_unlock(&kvm->mmu_lock);
+
 	return young;
 }
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d197b6725cb3..8d2d3acf18d8 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -901,7 +901,7 @@  static int kvm_mmu_notifier_clear_young(struct mmu_notifier *mn,
 	 * more sophisticated heuristic later.
 	 */
 	return kvm_handle_hva_range_no_flush(mn, start, end,
-					     kvm_age_gfn, false);
+					     kvm_age_gfn, true);
 }
 
 static int kvm_mmu_notifier_test_young(struct mmu_notifier *mn,
@@ -911,7 +911,7 @@  static int kvm_mmu_notifier_test_young(struct mmu_notifier *mn,
 	trace_kvm_test_age_hva(address);
 
 	return kvm_handle_hva_range_no_flush(mn, address, address + 1,
-					     kvm_test_age_gfn, false);
+					     kvm_test_age_gfn, true);
 }
 
 static void kvm_mmu_notifier_release(struct mmu_notifier *mn,