From nobody Sun Nov 24 14:02:44 2024 Received: from mail-yw1-f202.google.com (mail-yw1-f202.google.com [209.85.128.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 06A9C1F706F for ; Tue, 5 Nov 2024 18:43:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.202 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730832234; cv=none; b=NgUhATtqW5T7BftNNfgFT/lGD3aXMtZ/BrJHb+sx2S/uJSe6NU/VhE7klW09FHTPR4wXqzzD4cOaIxreF6uhpFMG+2sIEtHAmj3b60Kh1qaNdCW5jbWbK1XP7g+gePKkKrlkvC1QoXF1bl0sTZb/p0daes4qr26zzRFs+TToOZE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730832234; c=relaxed/simple; bh=jDUR0fdf4pyrS1yb6Btzmah8mkW5NwE4XOL0ct91PhM=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=krTAD1d7IzeDG8m/JZZuup1V362+QmdUHyiiiw9PYfNN21ViDFTZVHQ35YMwIySNUbof/k5UgPfIOO3Uu9jfWvWb1knVmJ+D071MpZYp7XF7pQTofsyby2schdUCwzf6sXkkDpMzIg7Qw4jKorVLbzKVPLZBUUgHRBi2qBoMHDc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--jthoughton.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=huBeBKNP; arc=none smtp.client-ip=209.85.128.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--jthoughton.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="huBeBKNP" Received: by mail-yw1-f202.google.com with SMTP id 00721157ae682-6e38fabff35so102508197b3.0 for ; Tue, 05 Nov 2024 10:43:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1730832232; x=1731437032; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=1iBajr2tvBcG6zm00BdC5Rt5Uo5VkPVaG6KrnUwYASM=; b=huBeBKNPPZNkN4sodNz4itHauoF/PQnTwiysZ7d7fRxrjl+UuOI9/yvK05quanVlhS zMjSmsBWaPb+8algPi/2mSu2fmrxtorWiftgiOK1v/9rzni/7uBvxJcQh37WaZ32ixwf z3mAGyQtO+FxEj4GsrOEJJoYgUT463x/26ehbWyxq6+lfPNY9DjGFhXW4qbAM2lXRb1t 8PPbU26VnMCzndvqducwtqPm6B1DGApdWTaTkSM0jjoL1j7EzLCF9Ebp5TebkV4iavnG hZg5SJg1XMeNzjvJK8Qtdv1pkwQ9a9EilDbC2g0kPqP0RUn+6vO54iofc9myyxsN8szW 9lMQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1730832232; x=1731437032; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=1iBajr2tvBcG6zm00BdC5Rt5Uo5VkPVaG6KrnUwYASM=; b=QuHn7q9MRAV1svDR42JbOZLXU7cpcIgyVQ1fAi9IFCp0jZCYE5Mav2WW+j3muQOQvz ea23YLuQkcMoWq9KxrPvi0gHZaYXaw+KhbkWHz5JJUizGrNCJCaeSHGiBBGX2Y7xnQaT 3gp/LG8w/R7KZVxWuTdX7vBi9+hR5Ehey0c7ETQUa+fC+A/paVxRe8lEd/9uPdZLGohx +zCE9nnZR+u6CKJdF04BSufb4h4DG4jOYkKSjOH+u77b+00ESOBFHMNhHb6cKz1jNwyr Ep98ZlsKFM3PGD/gznfQyopan5fAqOdkKEIUJ19c0hUISyJCdbQG8oQu7VXmN6AAoshG idKw== X-Forwarded-Encrypted: i=1; AJvYcCU2s7m3rlwzRQtwNPn38lVrsAuOhN0bI92mPjAzuuRnXyI8JQzg/hWHKDi1q2d4IhNCjvmUmevrBSzl/iA=@vger.kernel.org X-Gm-Message-State: AOJu0YxtW7Z4LKrz3ECTIwNcC25ij8swtgHOquIhJy3j0+ZiG3umn/QX lUDJzkqtZ7LjqUohMXFSPX3/eUqwVfAI0nOnxeSaJ4URUhONfb4LRN5BvTV5j5keoPIrIIJUL6F Esd8Fh8KouJEM5R0joQ== X-Google-Smtp-Source: AGHT+IEQCTYc5Qjt+z/Hb6r7J4If+mjo7L20fqiQ08ClH2OP7hcg4Onkoc+dim/QgXCvgp8uIzQynwLDxF2eMifJ X-Received: from jthoughton.c.googlers.com ([fda3:e722:ac3:cc00:13d:fb22:ac12:a84b]) (user=jthoughton job=sendgmr) by 2002:a05:690c:7091:b0:6ea:3c62:17c1 with SMTP id 00721157ae682-6ea3c621d20mr5673717b3.1.1730832232160; Tue, 05 Nov 2024 10:43:52 -0800 (PST) Date: Tue, 5 Nov 2024 18:43:31 +0000 In-Reply-To: <20241105184333.2305744-1-jthoughton@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241105184333.2305744-1-jthoughton@google.com> X-Mailer: git-send-email 2.47.0.199.ga7371fff76-goog Message-ID: <20241105184333.2305744-10-jthoughton@google.com> Subject: [PATCH v8 09/11] KVM: x86/mmu: Add support for lockless walks of rmap SPTEs From: James Houghton To: Sean Christopherson , Paolo Bonzini Cc: David Matlack , David Rientjes , James Houghton , Marc Zyngier , Oliver Upton , Wei Xu , Yu Zhao , Axel Rasmussen , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Sean Christopherson Add a lockless version of for_each_rmap_spte(), which is pretty much the same as the normal version, except that it doesn't BUG() the host if a non-present SPTE is encountered. When mmu_lock is held, it should be impossible for a different task to zap a SPTE, _and_ zapped SPTEs must be removed from their rmap chain prior to dropping mmu_lock. Thus, the normal walker BUG()s if a non-present SPTE is encountered as something is wildly broken. When walking rmaps without holding mmu_lock, the SPTEs pointed at by the rmap chain can be zapped/dropped, and so a lockless walk can observe a non-present SPTE if it runs concurrently with a different operation that is zapping SPTEs. Signed-off-by: Sean Christopherson Signed-off-by: James Houghton --- arch/x86/kvm/mmu/mmu.c | 75 +++++++++++++++++++++++------------------- 1 file changed, 42 insertions(+), 33 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 1cdb77df0a4d..71019762a28a 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -870,7 +870,7 @@ static struct kvm_memory_slot *gfn_to_memslot_dirty_bit= map(struct kvm_vcpu *vcpu */ #define KVM_RMAP_LOCKED BIT(1) =20 -static unsigned long kvm_rmap_lock(struct kvm_rmap_head *rmap_head) +static unsigned long __kvm_rmap_lock(struct kvm_rmap_head *rmap_head) { unsigned long old_val, new_val; =20 @@ -914,14 +914,25 @@ static unsigned long kvm_rmap_lock(struct kvm_rmap_he= ad *rmap_head) */ } while (!atomic_long_try_cmpxchg_acquire(&rmap_head->val, &old_val, new_= val)); =20 - /* Return the old value, i.e. _without_ the LOCKED bit set. */ + /* + * Return the old value, i.e. _without_ the LOCKED bit set. It's + * impossible for the return value to be 0 (see above), i.e. the read- + * only unlock flow can't get a false positive and fail to unlock. + */ return old_val; } =20 +static unsigned long kvm_rmap_lock(struct kvm *kvm, + struct kvm_rmap_head *rmap_head) +{ + lockdep_assert_held_write(&kvm->mmu_lock); + return __kvm_rmap_lock(rmap_head); +} + static void kvm_rmap_unlock(struct kvm_rmap_head *rmap_head, unsigned long new_val) { - WARN_ON_ONCE(new_val & KVM_RMAP_LOCKED); + KVM_MMU_WARN_ON(new_val & KVM_RMAP_LOCKED); /* * Ensure that all accesses to the rmap have completed * before we actually unlock the rmap. @@ -961,14 +972,14 @@ static void kvm_rmap_unlock_readonly(struct kvm_rmap_= head *rmap_head, /* * Returns the number of pointers in the rmap chain, not counting the new = one. */ -static int pte_list_add(struct kvm_mmu_memory_cache *cache, u64 *spte, - struct kvm_rmap_head *rmap_head) +static int pte_list_add(struct kvm *kvm, struct kvm_mmu_memory_cache *cach= e, + u64 *spte, struct kvm_rmap_head *rmap_head) { unsigned long old_val, new_val; struct pte_list_desc *desc; int count =3D 0; =20 - old_val =3D kvm_rmap_lock(rmap_head); + old_val =3D kvm_rmap_lock(kvm, rmap_head); =20 if (!old_val) { new_val =3D (unsigned long)spte; @@ -1048,7 +1059,7 @@ static void pte_list_remove(struct kvm *kvm, u64 *spt= e, unsigned long rmap_val; int i; =20 - rmap_val =3D kvm_rmap_lock(rmap_head); + rmap_val =3D kvm_rmap_lock(kvm, rmap_head); if (KVM_BUG_ON_DATA_CORRUPTION(!rmap_val, kvm)) goto out; =20 @@ -1092,7 +1103,7 @@ static bool kvm_zap_all_rmap_sptes(struct kvm *kvm, unsigned long rmap_val; int i; =20 - rmap_val =3D kvm_rmap_lock(rmap_head); + rmap_val =3D kvm_rmap_lock(kvm, rmap_head); if (!rmap_val) return false; =20 @@ -1184,23 +1195,18 @@ static u64 *rmap_get_first(struct kvm_rmap_head *rm= ap_head, struct rmap_iterator *iter) { unsigned long rmap_val =3D kvm_rmap_get(rmap_head); - u64 *sptep; =20 if (!rmap_val) return NULL; =20 if (!(rmap_val & KVM_RMAP_MANY)) { iter->desc =3D NULL; - sptep =3D (u64 *)rmap_val; - goto out; + return (u64 *)rmap_val; } =20 iter->desc =3D (struct pte_list_desc *)(rmap_val & ~KVM_RMAP_MANY); iter->pos =3D 0; - sptep =3D iter->desc->sptes[iter->pos]; -out: - BUG_ON(!is_shadow_present_pte(*sptep)); - return sptep; + return iter->desc->sptes[iter->pos]; } =20 /* @@ -1210,14 +1216,11 @@ static u64 *rmap_get_first(struct kvm_rmap_head *rm= ap_head, */ static u64 *rmap_get_next(struct rmap_iterator *iter) { - u64 *sptep; - if (iter->desc) { if (iter->pos < PTE_LIST_EXT - 1) { ++iter->pos; - sptep =3D iter->desc->sptes[iter->pos]; - if (sptep) - goto out; + if (iter->desc->sptes[iter->pos]) + return iter->desc->sptes[iter->pos]; } =20 iter->desc =3D iter->desc->more; @@ -1225,20 +1228,24 @@ static u64 *rmap_get_next(struct rmap_iterator *ite= r) if (iter->desc) { iter->pos =3D 0; /* desc->sptes[0] cannot be NULL */ - sptep =3D iter->desc->sptes[iter->pos]; - goto out; + return iter->desc->sptes[iter->pos]; } } =20 return NULL; -out: - BUG_ON(!is_shadow_present_pte(*sptep)); - return sptep; } =20 -#define for_each_rmap_spte(_rmap_head_, _iter_, _spte_) \ - for (_spte_ =3D rmap_get_first(_rmap_head_, _iter_); \ - _spte_; _spte_ =3D rmap_get_next(_iter_)) +#define __for_each_rmap_spte(_rmap_head_, _iter_, _sptep_) \ + for (_sptep_ =3D rmap_get_first(_rmap_head_, _iter_); \ + _sptep_; _sptep_ =3D rmap_get_next(_iter_)) + +#define for_each_rmap_spte(_rmap_head_, _iter_, _sptep_) \ + __for_each_rmap_spte(_rmap_head_, _iter_, _sptep_) \ + if (!WARN_ON_ONCE(!is_shadow_present_pte(*(_sptep_)))) \ + +#define for_each_rmap_spte_lockless(_rmap_head_, _iter_, _sptep_, _spte_) \ + __for_each_rmap_spte(_rmap_head_, _iter_, _sptep_) \ + if (is_shadow_present_pte(_spte_ =3D mmu_spte_get_lockless(sptep))) =20 static void drop_spte(struct kvm *kvm, u64 *sptep) { @@ -1324,12 +1331,13 @@ static bool __rmap_clear_dirty(struct kvm *kvm, str= uct kvm_rmap_head *rmap_head, struct rmap_iterator iter; bool flush =3D false; =20 - for_each_rmap_spte(rmap_head, &iter, sptep) + for_each_rmap_spte(rmap_head, &iter, sptep) { if (spte_ad_need_write_protect(*sptep)) flush |=3D test_and_clear_bit(PT_WRITABLE_SHIFT, (unsigned long *)sptep); else flush |=3D spte_clear_dirty(sptep); + } =20 return flush; } @@ -1650,7 +1658,7 @@ static void __rmap_add(struct kvm *kvm, kvm_update_page_stats(kvm, sp->role.level, 1); =20 rmap_head =3D gfn_to_rmap(gfn, sp->role.level, slot); - rmap_count =3D pte_list_add(cache, spte, rmap_head); + rmap_count =3D pte_list_add(kvm, cache, spte, rmap_head); =20 if (rmap_count > kvm->stat.max_mmu_rmap_size) kvm->stat.max_mmu_rmap_size =3D rmap_count; @@ -1796,13 +1804,14 @@ static unsigned kvm_page_table_hashfn(gfn_t gfn) return hash_64(gfn, KVM_MMU_HASH_SHIFT); } =20 -static void mmu_page_add_parent_pte(struct kvm_mmu_memory_cache *cache, +static void mmu_page_add_parent_pte(struct kvm *kvm, + struct kvm_mmu_memory_cache *cache, struct kvm_mmu_page *sp, u64 *parent_pte) { if (!parent_pte) return; =20 - pte_list_add(cache, parent_pte, &sp->parent_ptes); + pte_list_add(kvm, cache, parent_pte, &sp->parent_ptes); } =20 static void mmu_page_remove_parent_pte(struct kvm *kvm, struct kvm_mmu_pag= e *sp, @@ -2492,7 +2501,7 @@ static void __link_shadow_page(struct kvm *kvm, =20 mmu_spte_set(sptep, spte); =20 - mmu_page_add_parent_pte(cache, sp, sptep); + mmu_page_add_parent_pte(kvm, cache, sp, sptep); =20 /* * The non-direct sub-pagetable must be updated before linking. For --=20 2.47.0.199.ga7371fff76-goog