Re: [RFC PATCH 06/15] KVM: x86/mmu: Derive page role from parent

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On 11/20/21 00:57, David Matlack wrote:
Derive the page role from the parent shadow page, since the only thing
that changes is the level. This is in preparation for eagerly splitting
large pages during VM-ioctls which does not have access to the vCPU
MMU context.

No functional change intended.

Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
---
  arch/x86/kvm/mmu/tdp_mmu.c | 43 ++++++++++++++++++++------------------
  1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index b70707a7fe87..1a409992a57f 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -157,23 +157,8 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
  		if (kvm_mmu_page_as_id(_root) != _as_id) {		\
  		} else
-static union kvm_mmu_page_role page_role_for_level(struct kvm_vcpu *vcpu,
-						   int level)
-{
-	union kvm_mmu_page_role role;
-
-	role = vcpu->arch.mmu->mmu_role.base;
-	role.level = level;
-	role.direct = true;
-	role.gpte_is_8_bytes = true;
-	role.access = ACC_ALL;
-	role.ad_disabled = !shadow_accessed_mask;
-
-	return role;
-}
-
  static struct kvm_mmu_page *alloc_tdp_mmu_page(struct kvm_vcpu *vcpu, gfn_t gfn,
-					       int level)
+					       union kvm_mmu_page_role role)
  {
  	struct kvm_mmu_memory_caches *mmu_caches;
  	struct kvm_mmu_page *sp;
@@ -184,7 +169,7 @@ static struct kvm_mmu_page *alloc_tdp_mmu_page(struct kvm_vcpu *vcpu, gfn_t gfn,
  	sp->spt = kvm_mmu_memory_cache_alloc(&mmu_caches->shadow_page_cache);
  	set_page_private(virt_to_page(sp->spt), (unsigned long)sp);
- sp->role.word = page_role_for_level(vcpu, level).word;
+	sp->role = role;
  	sp->gfn = gfn;
  	sp->tdp_mmu_page = true;
@@ -193,6 +178,19 @@ static struct kvm_mmu_page *alloc_tdp_mmu_page(struct kvm_vcpu *vcpu, gfn_t gfn,
  	return sp;
  }
+static struct kvm_mmu_page *alloc_child_tdp_mmu_page(struct kvm_vcpu *vcpu, struct tdp_iter *iter)
+{
+	struct kvm_mmu_page *parent_sp;
+	union kvm_mmu_page_role role;
+
+	parent_sp = sptep_to_sp(rcu_dereference(iter->sptep));
+
+	role = parent_sp->role;
+	role.level--;
+
+	return alloc_tdp_mmu_page(vcpu, iter->gfn, role);
+}
+
  hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu)
  {
  	union kvm_mmu_page_role role;
@@ -201,7 +199,12 @@ hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu)
lockdep_assert_held_write(&kvm->mmu_lock); - role = page_role_for_level(vcpu, vcpu->arch.mmu->shadow_root_level);
+	role = vcpu->arch.mmu->mmu_role.base;
+	role.level = vcpu->arch.mmu->shadow_root_level;
+	role.direct = true;
+	role.gpte_is_8_bytes = true;
+	role.access = ACC_ALL;
+	role.ad_disabled = !shadow_accessed_mask;

I have a similar patch for the old MMU, but it was also replacing shadow_root_level with shadow_root_role. I'll see if I can adapt it to the TDP MMU, since the shadow_root_role is obviously the same for both.

Paolo

  	/* Check for an existing root before allocating a new one. */
  	for_each_tdp_mmu_root(kvm, root, kvm_mmu_role_as_id(role)) {
@@ -210,7 +213,7 @@ hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu)
  			goto out;
  	}
- root = alloc_tdp_mmu_page(vcpu, 0, vcpu->arch.mmu->shadow_root_level);
+	root = alloc_tdp_mmu_page(vcpu, 0, role);
  	refcount_set(&root->tdp_mmu_root_count, 1);
spin_lock(&kvm->arch.tdp_mmu_pages_lock);
@@ -1028,7 +1031,7 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
  			if (is_removed_spte(iter.old_spte))
  				break;
- sp = alloc_tdp_mmu_page(vcpu, iter.gfn, iter.level - 1);
+			sp = alloc_child_tdp_mmu_page(vcpu, &iter);
  			if (!tdp_mmu_install_sp_atomic(vcpu->kvm, &iter, sp, account_nx))
  				break;
  		}




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