From nobody Fri Nov 29 03:31:46 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 2F80818E743 for ; Thu, 26 Sep 2024 01:35:26 +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=1727314529; cv=none; b=uP42Hqa9hez33S0fHt6KiiyrIpBn80R9DOxVQVQQyFvKyOoMprSKKkoA01nvddi0UwehJ6xjcQbFrN1Nz+XM0zTZTzzzoZcc6SrrgeG8Z20eSXVw7vWngz7BXE+iF0aGt0zg0RzDX8ZuB/HCoSvd4x5aYBqXbePLpB2BK6BeVEo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727314529; c=relaxed/simple; bh=0raPSAp7HnmbBOxblzsQepM7TqKA7NY1yCc61VEgCKk=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=lm+OjA0xuROBgiOK81n69CPBn/jbNXTlY+z+5ma6V5wxcojjeObbWID/T6xYxkS96/7zgdKJopQ8w64jPECuVvN28x2l1P/1aLce6cyLVhNGApPmTDpXI4pcHBQRBY4pvQQChx8pIKORtEbSlUY2Ubi5mtDb5cpOHhiJZcYIYqU= 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=m/VTRhi4; 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="m/VTRhi4" Received: by mail-yw1-f202.google.com with SMTP id 00721157ae682-6e230808388so6923347b3.0 for ; Wed, 25 Sep 2024 18:35:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1727314526; x=1727919326; 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=MfYThc4u3zoEwhsYqTZzHZoRr9LypPNnm95GFpy1spA=; b=m/VTRhi4Vb+l3sQ9+TsKzd34SVYj5ofUYIRw29d46kdZg/s++sbiH2HxV6TUSI+WVe qrvHnx2MdK5vGGg7epJE12uX2HJOeFDslmOQvTk+RW6WJqC/GIttuF5sNSWF2IDe6r84 Oyl3FwIKr2RwMmIGCk06foCowlPWYirhsg5auSAa1k2dFNi/fcTElYCMWW0g9JrQCR8Q RnZw2JSWLo2sbZpZx2YFITuhzBYe2UAHX3CfkY8Ofe7gULoecF/Wfp1c+cyBdt5dJB8M Z9MCwdscIWgwu8MHVeq7SYR0pGIa7TpFAEsABLL5UCGNWygeUXj11bZIfoczL/UeldZR DvPw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1727314526; x=1727919326; 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=MfYThc4u3zoEwhsYqTZzHZoRr9LypPNnm95GFpy1spA=; b=XikkU4OrGjozlhwjuKRNll0RPPrZqrvmyyweImpgQtgzEYswK0fVFrGCKxkRP6UHhK w8s8s3cCzZxPslPkvarZoFUFz81HFc4UYbKK3aN7oHF9mgiwDjIPokzwwOlsatbSj7j8 Lz6wGQcahhSYtRXwaxHLP7f+iugIODFS1T1qBq9Zq2Px7KycRjlHpFI2ndRDRtq+NDLK a9mM0tg7RQ0Yyx2SGgK99GQGaoV50noLeYXELMCWZkM+grus1udB50qvl4kyz0zKgddS ZkUebcnjsM3ItZC6BYvGiLg1VkjiDdIXZx10aBUDEq6ajEWIDys7QiUo8COPlxPRbhKr Eoaw== X-Forwarded-Encrypted: i=1; AJvYcCVCUmut3bWzNZmXk86Qh/rjhwRSnTI3HMuoSDGANCPyjm3FJcAFvrRbpdv+GE0IfvSbnlk6EHnyZN1p4IU=@vger.kernel.org X-Gm-Message-State: AOJu0Yx6pHwGRftxO2tyhewPkBiyGjuKT8CnEYSEVyVoqC4wVPQyKNUz 6S6zANMXly71y2iLhIdbxqWluZskJGNs2SndHwtUIQDbsr1VpJLncmyA7uf34t7hfTKVm4Cl90+ yoouNF5iV3P54a+FYdw== X-Google-Smtp-Source: AGHT+IFc2BTb/n/6/Pa4YiRnYJohGJI1GOQLPmGDGx2avUwnGUEvHFpkm5PUE1m++wXUG9sRJDYpg95gpRMXrHPb X-Received: from jthoughton.c.googlers.com ([fda3:e722:ac3:cc00:13d:fb22:ac12:a84b]) (user=jthoughton job=sendgmr) by 2002:a05:690c:5086:b0:6e2:1b8c:39bf with SMTP id 00721157ae682-6e21d835b06mr289447b3.2.1727314525948; Wed, 25 Sep 2024 18:35:25 -0700 (PDT) Date: Thu, 26 Sep 2024 01:34:57 +0000 In-Reply-To: <20240926013506.860253-1-jthoughton@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240926013506.860253-1-jthoughton@google.com> X-Mailer: git-send-email 2.46.0.792.g87dc391469-goog Message-ID: <20240926013506.860253-10-jthoughton@google.com> Subject: [PATCH v7 09/18] KVM: x86/mmu: Add support for lockless walks of rmap SPTEs From: James Houghton To: Sean Christopherson , Paolo Bonzini Cc: Andrew Morton , David Matlack , David Rientjes , James Houghton , Jason Gunthorpe , Jonathan Corbet , Marc Zyngier , Oliver Upton , Wei Xu , Yu Zhao , Axel Rasmussen , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.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 [jthoughton: Added lockdep assertion for kvm_rmap_lock, synchronization fix= up] 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 79676798ba77..72c682fa207a 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -932,7 +932,7 @@ 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 @@ -976,14 +976,25 @@ 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. @@ -1023,14 +1034,14 @@ static void kvm_rmap_unlock_readonly(struct kvm_rma= p_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; @@ -1110,7 +1121,7 @@ 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 @@ -1154,7 +1165,7 @@ 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 @@ -1246,23 +1257,18 @@ 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 /* @@ -1272,14 +1278,11 @@ 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; @@ -1287,20 +1290,24 @@ 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) { @@ -1396,11 +1403,12 @@ 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 spte_wrprot_for_clear_dirty(sptep); else flush |=3D spte_clear_dirty(sptep); + } =20 return flush; } @@ -1710,7 +1718,7 @@ 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; @@ -1859,13 +1867,14 @@ 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, @@ -2555,7 +2564,7 @@ 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 2.46.0.792.g87dc391469-goog