From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f73.google.com (mail-pj1-f73.google.com [209.85.216.73]) (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 EE08C1EB192 for ; Fri, 7 Feb 2025 15:12:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.73 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738941128; cv=none; b=h4B7zcJMUYnBeDpO9TWj3T6jy/mrvMyCAqZ+2sdk3gbG8OstV/WBc5v3VOsVNnw+AklhFbYAwcjKtG4QDr/YFdkkYCP92jAoj0R0Sc4r7K9SlwX3jruR49SqII4M3oNjp1rdgEliLxMF/cHd0fthtfC35vkO3/iici+F/jBGRvY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738941128; c=relaxed/simple; bh=7WeBIy2sejYk+BR4w9p25NFRkBTZIswmq3mry9An0iw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=oRuDGPPSscO/EC9oIvC544wEvzI5X9j0f/s2BdoYNdoDo7w70i7tjbVqckbBXLQGR4tToVr23jHjDrQSvOXH6QC9VVmYFOPkGOW41quWsDaZwXKw0IgaarwSbWa8awAqKckG3TLLs1/vxBYI7OlxGIob2ky2TYCAQxNwwhUq8Mo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=M/Tk/r+P; arc=none smtp.client-ip=209.85.216.73 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--seanjc.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/Tk/r+P" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-2fa32e4044bso873210a91.0 for ; Fri, 07 Feb 2025 07:12:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1738941126; x=1739545926; 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=LxVXEzr2oQzIGSnyax9BmL0hTrsx3WZN3f0e41uCa0k=; b=M/Tk/r+PPIisRQBBW2/p+0l7LRkGjGwrCUiizFkYwTEZ2nC+Pwruubw8KKEke4lO6J VzsJXYFOGxI4c89CzbMYIAdzaQ7EGNmkdV0K2kdIxBI3w9z96U/0SwhO5OrLe+w9NV7I shq6baIghdCk5CkeRDALH4Fy6M7IZqkTbn6b/FjvJ6MWxRoU5ZzOUM5Rr63VrQ1lf/O9 xR+JuFTWuGCeqnHwgnU7ErAuqQvWWE1Nz0R9eUgLzMFs/FM19F8ty3VpWtrb5wZVTTn+ T3K+QJBDlfrOZh1r1uuY8KdpFSepD0abZWAmRoNxZr3+j8UPBoIjAuncs+VvGAlxouoC A1Vw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1738941126; x=1739545926; 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=LxVXEzr2oQzIGSnyax9BmL0hTrsx3WZN3f0e41uCa0k=; b=JWrIj++FrjIsRCqZUdvDHTeZnXnuIcru4vohWLujTT43zZaeIlyk3zGQqjCsKzoldb XGGpO9HdjjbEhQ4pMOeCW9OYlilQq214ITw2dxeaHLmtz4JNvV+Xp50Svja8Jk/2uUgJ UGTALmKv04jaEF1fjMOfDoQ77ET9S0ys70cCv0hclrBp3bVjn03MVFnC9G0sVntsHsde kFwSZguN8kKShWT2p2ltIcsI/C/xy9iDS6qcn3u63+ScXMbpqzAI86NLBUNLX7lKMrwq G9Pst7h44daNDsNU/C7Krir7vZUbmNY8eFXdHvx7/8JM8u+L83yyV3po+iVt46wFXwfx X/YQ== X-Forwarded-Encrypted: i=1; AJvYcCUd3GlL/Qzfue4jcRvuTWMDjrLkKUvr9C/zHAbie/1jht6mHiQKQx7qw9vFb8S9nmO7ERA=@vger.kernel.org X-Gm-Message-State: AOJu0YzPPLFHDMvbzH8nq6ytKXTljDDqBqTNhFWz1a0J1hERQdniKk7K EQVfKNzHbpcq2FBBNzz3G1QQzvZ8UK8JypZgeU9Fs6PXIswzWUpM/krQ/CSJppAc013NnZrMhGa 6ZQ== X-Google-Smtp-Source: AGHT+IFGLXHzNrNOdKG1czY4jTF73FsqIGqlSCN04qJ3RgdhuYV6jC13Lajj/ww4zk3yzh9N7Wq07gYnLLg= X-Received: from pjbee11.prod.google.com ([2002:a17:90a:fc4b:b0:2f2:e97a:e77f]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:1e41:b0:2ee:a583:e616 with SMTP id 98e67ed59e1d1-2fa24064ed1mr5606353a91.9.1738941126259; Fri, 07 Feb 2025 07:12:06 -0800 (PST) Date: Fri, 7 Feb 2025 07:12:04 -0800 In-Reply-To: <20250207030931.1902-1-yan.y.zhao@intel.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250207030640.1585-1-yan.y.zhao@intel.com> <20250207030931.1902-1-yan.y.zhao@intel.com> Message-ID: Subject: Re: [PATCH 4/4] KVM: x86/mmu: Free obsolete roots when pre-faulting SPTEs From: Sean Christopherson To: Yan Zhao Cc: pbonzini@redhat.com, rick.p.edgecombe@intel.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Fri, Feb 07, 2025, Yan Zhao wrote: > Always free obsolete roots when pre-faulting SPTEs in case it's called > after a root is invalidated (e.g., by memslot removal) but before any > vcpu_enter_guest() processing of KVM_REQ_MMU_FREE_OBSOLETE_ROOTS. > > Lack of kvm_mmu_free_obsolete_roots() in this scenario can lead to > kvm_mmu_reload() failing to load a new root if the current root hpa is an > obsolete root (which is not INVALID_PAGE). Consequently, > kvm_arch_vcpu_pre_fault_memory() will retry infinitely due to the checking > of is_page_fault_stale(). > > It's safe to call kvm_mmu_free_obsolete_roots() even if there are no > obsolete roots or if it's called a second time when vcpu_enter_guest() > later processes KVM_REQ_MMU_FREE_OBSOLETE_ROOTS. This is because > kvm_mmu_free_obsolete_roots() sets an obsolete root to INVALID_PAGE and > will do nothing to an INVALID_PAGE. Why is userspace changing memslots while prefaulting? > > Signed-off-by: Yan Zhao > --- > arch/x86/kvm/mmu/mmu.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 47fd3712afe6..72f68458049a 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -4740,7 +4740,12 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, > /* > * reload is efficient when called repeatedly, so we can do it on > * every iteration. > + * Before reload, free obsolete roots in case the prefault is called > + * after a root is invalidated (e.g., by memslot removal) but > + * before any vcpu_enter_guest() processing of > + * KVM_REQ_MMU_FREE_OBSOLETE_ROOTS. > */ > + kvm_mmu_free_obsolete_roots(vcpu); > r = kvm_mmu_reload(vcpu); > if (r) > return r; I would prefer to do check for obsolete roots in kvm_mmu_reload() itself, but keep the main kvm_check_request() so that the common case handles the resulting TLB flush without having to loop back around in vcpu_enter_guest(). diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h index 050a0e229a4d..f2b36d32ef40 100644 --- a/arch/x86/kvm/mmu.h +++ b/arch/x86/kvm/mmu.h @@ -104,6 +104,9 @@ void kvm_mmu_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new, static inline int kvm_mmu_reload(struct kvm_vcpu *vcpu) { + if (kvm_check_request(KVM_REQ_MMU_FREE_OBSOLETE_ROOTS, vcpu)) + kvm_mmu_free_obsolete_roots(vcpu); + /* * Checking root.hpa is sufficient even when KVM has mirror root. * We can have either: