From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f201.google.com (mail-pf1-f201.google.com [209.85.210.201]) (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 37972348871 for ; Tue, 21 Oct 2025 16:36:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761064616; cv=none; b=R00xA3Th8mMn+NxW0Va45vUWm7Qv4qg7orRNL8PB5UL+e6SPn1jr+Im4lqoitzclQiYjjD0+wKqNlsuSOy0GFDzGUnoqMZCRinx131nvu2ZXUxdELpZQO+Oz7/aZrjFo/NV0kuWO3k4MXcPCrXHgxZcSpuoS9ao3MqO3teUcByg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761064616; c=relaxed/simple; bh=V8VPj9cMcUrASFrIP3Xcl8Z1vzjTesRqQ0IhhfznT5E=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=GIghT9P8tUxbbqMkLWXNZHLE46oI5W9bVepL4DHDrPKQOk23MqA4/dtGcSmzO7LPV4Ch52KaYsBT7gBj5zHd/uvTGXi6yGIiy5QM61J6yKT0g6NP1rO3LW1qaQc7zZg4edCrEVgg4DPZLwDN8DqW+wXgBT4JK+TX8rJRPNWpIxM= 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=IzxN9l67; arc=none smtp.client-ip=209.85.210.201 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="IzxN9l67" Received: by mail-pf1-f201.google.com with SMTP id d2e1a72fcca58-7810e5a22f3so11992043b3a.1 for ; Tue, 21 Oct 2025 09:36:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1761064613; x=1761669413; darn=lists.linux.dev; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=z/IdadGFev8EMGQWIIqEHXt78w+GzasFDdOM6t/N/dU=; b=IzxN9l67TpWaLl06STKKq/RfE9beb6t4wZ2MuvW6FMJGPzNHqUFZLup8C0nHsyffZ6 ZTUwF/v2tTPNGXW+3nymqUMDZNkchZNfv1g9xoX1Z7LRB5MLtzraGwxXwfeelIngJxAf vfMlHQ8dopvY4sN1t+c2w8xquhobjqZiKi+WNuImJ363qkA7mSwNkhVKS5+bRn4In2ZW PcjQHeqk/Secz5XAoIaaA6UflT58/YKL/geNR6ju3RYdWIruRGkkAu2hudVHFg6xdvP/ Va5uTLAHRGKToGvLO1Qszh+p4Rr6sC5W7BIvNdHbQa1ppSAAKB4sX3phWtI+tUmwIuor XViw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1761064613; x=1761669413; 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=z/IdadGFev8EMGQWIIqEHXt78w+GzasFDdOM6t/N/dU=; b=dzulSwS2TrVqyi2VeNyDoFRqyCLMW+vA/ybWmMB6CXfbf2xlLwDDZV2XkKN2m14hqu t5b/snSk/Lpud+o/0qZ+ebce61IxTxlItpL1bRVTLFiWEI1hC2kDFCji0vX0Gnpt1+s+ rG2csBqXt3DXUR2itPGF2DSm1LqmWbP4f98KE3AAm5lg+Q+JDcloIDIjm0jyqk+7qufe 4z++hh1ej2aAZpnXRsRAVtNJeJ4xXMk62XHnlhqL91Y0DHAm8JQ5u3guLVCe46bLsoUn KQ06dUAC+WvE87qZHBBUwihoPAlIlpCsZ7LWYLH8E09Ic99Vgl7ohDY/v8lphw5qEhU3 55dA== X-Forwarded-Encrypted: i=1; AJvYcCV0K6cqKvXhQ03l9hILzh2jX3MaLpCX93XAFym2ypX62NMA4aSm8ERnefakaDhimE0sgWgAgpk=@lists.linux.dev X-Gm-Message-State: AOJu0YyEK5YLdFR5Ok+AaRHk8DujCCNmzHjxzo+77WjtGNJgs8+EVnmR ymRdEJjj+vpz2Q+aBZGqT8pWVPioznDBmm+DjyN/owXVw+eEX3cGLTQHhebFj2TWIHKYrikpcgp 1mvj9QQ== X-Google-Smtp-Source: AGHT+IES6ELYoVnXS8by0geR6jOr+Qyair+TP7lX0bGCC8OGD3dU25vj5A6KyxRj4XG+s9p6uoHaw2v+jQs= X-Received: from pjbnk17.prod.google.com ([2002:a17:90b:1951:b0:32e:ca6a:7ca9]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:3d0b:b0:32b:7220:8536 with SMTP id adf61e73a8af0-334a856d5bbmr22480858637.16.1761064613440; Tue, 21 Oct 2025 09:36:53 -0700 (PDT) Date: Tue, 21 Oct 2025 09:36:52 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20251017003244.186495-1-seanjc@google.com> <20251017003244.186495-5-seanjc@google.com> Message-ID: Subject: Re: [PATCH v3 04/25] KVM: x86/mmu: Add dedicated API to map guest_memfd pfn into TDP MMU From: Sean Christopherson To: Yan Zhao Cc: Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Huacai Chen , Madhavan Srinivasan , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Paolo Bonzini , "Kirill A. Shutemov" , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, x86@kernel.org, linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, Ira Weiny , Kai Huang , Michael Roth , Vishal Annapurve , Rick Edgecombe , Ackerley Tng , Binbin Wu Content-Type: text/plain; charset="us-ascii" On Tue, Oct 21, 2025, Yan Zhao wrote: > On Thu, Oct 16, 2025 at 05:32:22PM -0700, Sean Christopherson wrote: > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > > index 18d69d48bc55..ba5cca825a7f 100644 > > --- a/arch/x86/kvm/mmu/mmu.c > > +++ b/arch/x86/kvm/mmu/mmu.c > > @@ -5014,6 +5014,65 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, > > return min(range->size, end - range->gpa); > > } > > > > +int kvm_tdp_mmu_map_private_pfn(struct kvm_vcpu *vcpu, gfn_t gfn, kvm_pfn_t pfn) > > +{ > > + struct kvm_page_fault fault = { > > + .addr = gfn_to_gpa(gfn), > > + .error_code = PFERR_GUEST_FINAL_MASK | PFERR_PRIVATE_ACCESS, > > + .prefetch = true, > > + .is_tdp = true, > > + .nx_huge_page_workaround_enabled = is_nx_huge_page_enabled(vcpu->kvm), > > + > > + .max_level = PG_LEVEL_4K, > > + .req_level = PG_LEVEL_4K, > > + .goal_level = PG_LEVEL_4K, > > + .is_private = true, > > + > > + .gfn = gfn, > > + .slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn), > > + .pfn = pfn, > > + .map_writable = true, > > + }; > > + struct kvm *kvm = vcpu->kvm; > > + int r; > > + > > + lockdep_assert_held(&kvm->slots_lock); > Do we need to assert that filemap_invalidate_lock() is held as well? Hrm, a lockdep assertion would be nice to have, but it's obviously not strictly necessary, and I'm not sure it's worth the cost. To safely assert, KVM would need to first assert that the file refcount is elevated, e.g. to guard against guest_memfd _really_ screwing up and not grabbing a reference to the underlying file. E.g. it'd have to be something like this: diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 94d7f32a03b6..5d46b2ac0292 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -5014,6 +5014,18 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, return min(range->size, end - range->gpa); } +static void kvm_assert_gmem_invalidate_lock_held(struct kvm_memory_slot *slot) +{ +#ifdef CONFIG_PROVE_LOCKING + if (WARN_ON_ONCE(!kvm_slot_has_gmem(slot)) || + WARN_ON_ONCE(!slot->gmem.file) || + WARN_ON_ONCE(!file_count(slot->gmem.file))) + return; + + lockdep_assert_held(file_inode(&slot->gmem.file)->i_mapping->invalidate_lock)); +#endif +} + int kvm_tdp_mmu_map_private_pfn(struct kvm_vcpu *vcpu, gfn_t gfn, kvm_pfn_t pfn) { struct kvm_page_fault fault = { @@ -5038,6 +5050,8 @@ int kvm_tdp_mmu_map_private_pfn(struct kvm_vcpu *vcpu, gfn_t gfn, kvm_pfn_t pfn) lockdep_assert_held(&kvm->slots_lock); + kvm_assert_gmem_invalidate_lock_held(fault.slot); + if (KVM_BUG_ON(!tdp_mmu_enabled, kvm)) return -EIO; -- Which I suppose isn't that terrible?