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Reply-To: Sean Christopherson <seanjc@google.com>
Date: Tue, 1 Apr 2025 08:57:14 -0700
In-Reply-To: <20250401155714.838398-1-seanjc@google.com>
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Message-ID: <20250401155714.838398-4-seanjc@google.com>
Subject: [PATCH v2 3/3] KVM: x86/mmu: Defer allocation of shadow MMU's hashed
page list
From: Sean Christopherson <seanjc@google.com>
To: Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Vipin Sharma <vipinsh@google.com>
Content-Transfer-Encoding: quoted-printable
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When the TDP MMU is enabled, i.e. when the shadow MMU isn't used until a
nested TDP VM is run, defer allocation of the array of hashed lists used
to track shadow MMU pages until the first shadow root is allocated.
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/mmu/mmu.c | 40 ++++++++++++++++++++++++++++++----------
1 file changed, 30 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6b9c72405860..213009cdba15 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1982,14 +1982,25 @@ static bool sp_has_gptes(struct kvm_mmu_page *sp)
return true;
}
=20
+static __ro_after_init HLIST_HEAD(empty_page_hash);
+
+static struct hlist_head *kvm_get_mmu_page_hash(struct kvm *kvm, gfn_t gfn)
+{
+ struct hlist_head *page_hash =3D READ_ONCE(kvm->arch.mmu_page_hash);
+
+ if (!page_hash)
+ return &empty_page_hash;
+
+ return &page_hash[kvm_page_table_hashfn(gfn)];
+}
+
#define for_each_valid_sp(_kvm, _sp, _list) \
hlist_for_each_entry(_sp, _list, hash_link) \
if (is_obsolete_sp((_kvm), (_sp))) { \
} else
=20
#define for_each_gfn_valid_sp_with_gptes(_kvm, _sp, _gfn) \
- for_each_valid_sp(_kvm, _sp, \
- &(_kvm)->arch.mmu_page_hash[kvm_page_table_hashfn(_gfn)]) \
+ for_each_valid_sp(_kvm, _sp, kvm_get_mmu_page_hash(_kvm, _gfn)) \
if ((_sp)->gfn !=3D (_gfn) || !sp_has_gptes(_sp)) {} else
=20
static bool kvm_sync_page_check(struct kvm_vcpu *vcpu, struct kvm_mmu_page=
*sp)
@@ -2357,6 +2368,7 @@ static struct kvm_mmu_page *__kvm_mmu_get_shadow_page=
(struct kvm *kvm,
struct kvm_mmu_page *sp;
bool created =3D false;
=20
+ BUG_ON(!kvm->arch.mmu_page_hash);
sp_list =3D &kvm->arch.mmu_page_hash[kvm_page_table_hashfn(gfn)];
=20
sp =3D kvm_mmu_find_shadow_page(kvm, vcpu, gfn, sp_list, role);
@@ -3884,11 +3896,14 @@ static int kvm_mmu_alloc_page_hash(struct kvm *kvm)
{
typeof(kvm->arch.mmu_page_hash) h;
=20
+ if (kvm->arch.mmu_page_hash)
+ return 0;
+
h =3D kcalloc(KVM_NUM_MMU_PAGES, sizeof(*h), GFP_KERNEL_ACCOUNT);
if (!h)
return -ENOMEM;
=20
- kvm->arch.mmu_page_hash =3D h;
+ WRITE_ONCE(kvm->arch.mmu_page_hash, h);
return 0;
}
=20
@@ -3911,9 +3926,13 @@ static int mmu_first_shadow_root_alloc(struct kvm *k=
vm)
if (kvm_shadow_root_allocated(kvm))
goto out_unlock;
=20
+ r =3D kvm_mmu_alloc_page_hash(kvm);
+ if (r)
+ goto out_unlock;
+
/*
- * Check if anything actually needs to be allocated, e.g. all metadata
- * will be allocated upfront if TDP is disabled.
+ * Check if memslot metadata actually needs to be allocated, e.g. all
+ * metadata will be allocated upfront if TDP is disabled.
*/
if (kvm_memslots_have_rmaps(kvm) &&
kvm_page_track_write_tracking_enabled(kvm))
@@ -6694,12 +6713,13 @@ int kvm_mmu_init_vm(struct kvm *kvm)
INIT_LIST_HEAD(&kvm->arch.possible_nx_huge_pages);
spin_lock_init(&kvm->arch.mmu_unsync_pages_lock);
=20
- r =3D kvm_mmu_alloc_page_hash(kvm);
- if (r)
- return r;
-
- if (tdp_mmu_enabled)
+ if (tdp_mmu_enabled) {
kvm_mmu_init_tdp_mmu(kvm);
+ } else {
+ r =3D kvm_mmu_alloc_page_hash(kvm);
+ if (r)
+ return r;
+ }
=20
kvm->arch.split_page_header_cache.kmem_cache =3D mmu_page_header_cache;
kvm->arch.split_page_header_cache.gfp_zero =3D __GFP_ZERO;
--=20
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