From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f73.google.com (mail-wr1-f73.google.com [209.85.221.73]) (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 29FF22DFA46 for ; Wed, 23 Jul 2025 10:47:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.73 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753267649; cv=none; b=noIWv9+2Q+bGMC1D43DNZWAGTn/lNSZVaxcJG/qRtwlERz6Y27akmaV8vCtWVfqQCrJNQotniWKbhKDuKhduyvOzSUwGmGENoNK5Kq49HbpC0FiY7JyX9CDwM3D+FUyePma3qya9UhoMcXXcpwlrxsobyFO2gc7H8a5DByxvobw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753267649; c=relaxed/simple; bh=QyxuUTWdkqfWwCRIlgMMsPpjhtM2I7WKCTsedQOzWL0=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=giC2z5z2w+xaUfuZzmgh/JjmYbRrU/OAmrnShWui24FXvt+kPiRfoPmp9jRHusTAtLhH7fwaqogxdDK9cvUuCyTSzog6QgpvolDH4rwB9jTxvCbXgSWNmyGrG7wOYF1s8rTiNi48mC+bQGe+YZ4duwzYBhLvFHTVEGLk+Wa8MTQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--tabba.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=RSbBTEVi; arc=none smtp.client-ip=209.85.221.73 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--tabba.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="RSbBTEVi" Received: by mail-wr1-f73.google.com with SMTP id ffacd0b85a97d-3a58939191eso2794976f8f.0 for ; Wed, 23 Jul 2025 03:47:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1753267645; x=1753872445; 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=fcETzHTWiEWR8GOIStOaS7XhZknr1voGGAhaPeQn9wI=; b=RSbBTEVipKeQfV3I7Y0Edl/ZqHt6EUPW4wh/BSOU333+PRpKkLQAsKvHO5E6WjCgLL 5SJ1G1GeLAdtQCkydutJS6awn4V2JPhTp90KxcOj63P7Jq5GwGDYuHJDPzOIsfQJeX6r c788YIYPrUm6cvOW6KvrahQ8ftFxikn8JfApzJ94HBAFhWDcS3fylrflJyOu8+SQdf4Y sucAUm7MSyQZ9MK/U9Yv5r9n/wLLcahYXHyC6nd+hCQB6RCdyqU80+Q2s/RUraiU9mZV D4qN6bTe8SrUr7I2hQI48lR/6SL1/KQxWzND2fhaMveGec2eJ0y65mG8BSBitTHb+3e2 4j+A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1753267645; x=1753872445; 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=fcETzHTWiEWR8GOIStOaS7XhZknr1voGGAhaPeQn9wI=; b=jV5st0eqo6xCnaLO7lTTHV03RYQLUqdjbP0M0VZy4wOTRWa58Tsr7JeM7KPt4bNPMG z33+CfN2lPkZaBAbkVhkpwifJkNmSASoBJWf+aYd39Waj9SzXcJcRf4b+fiK8f3HeVOX SgeVmMpECq2ReKXjn6Xv5+hO/POov9m6bFR70ufUCRptqh1/aqEhNJD73h0dzzGnTgYz KjJ0sIO8TkkQ6W3mhE0EkjUomDcdZmtR6NLpGyv2PSc9iX33lzcfh/d7jHSp1RVpRxgy qbHuBKxkAPI91b2YdIWwaS8JLzfMOu7bK3TxX2SI+OhYWxRWRvLmMR5Zn8i+9f7GKozt TqeA== X-Forwarded-Encrypted: i=1; AJvYcCWl1Bw5njYbHHSl6MSnYuDtVnl7UwTE8DH34sEvniNqDES0ESZvilXj1ASFuWW52FDY/MyGh7s=@lists.linux.dev X-Gm-Message-State: AOJu0Yy+QarVRmaPU1nJDrbD4OQNQePDa1m6FYOTYnQYB100Tvxd1LKO xtm1Ox2dawV6CSTJfYA7MOsnoV2MLIqfGvFwAz1sjRUaTwrrU65whYZOoqLs+AuUtLO1ktxuGRM xEQ== X-Google-Smtp-Source: AGHT+IEe44MXl/ytA6bQwQoEc18ccfi02+HhAg/vYEYD6fmTIl5PZmuGxIaMa7BS20QwG080yszRIEU/kg== X-Received: from wrbfx9.prod.google.com ([2002:a05:6000:2d09:b0:3a5:2220:5be3]) (user=tabba job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6000:230d:b0:3b3:9c56:b834 with SMTP id ffacd0b85a97d-3b768c9d38dmr1845396f8f.1.1753267645473; Wed, 23 Jul 2025 03:47:25 -0700 (PDT) Date: Wed, 23 Jul 2025 11:47:02 +0100 In-Reply-To: <20250723104714.1674617-1-tabba@google.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250723104714.1674617-1-tabba@google.com> X-Mailer: git-send-email 2.50.1.470.g6ba607880d-goog Message-ID: <20250723104714.1674617-11-tabba@google.com> Subject: [PATCH v16 10/22] KVM: guest_memfd: Add plumbing to host to map guest_memfd pages From: Fuad Tabba To: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, kvmarm@lists.linux.dev Cc: pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, xiaoyao.li@intel.com, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, ackerleytng@google.com, mail@maciej.szmigiero.name, david@redhat.com, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, roypat@amazon.co.uk, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com, peterx@redhat.com, pankaj.gupta@amd.com, ira.weiny@intel.com, tabba@google.com Content-Type: text/plain; charset="UTF-8" Introduce the core infrastructure to enable host userspace to mmap() guest_memfd-backed memory. This is needed for several evolving KVM use cases: * Non-CoCo VM backing: Allows VMMs like Firecracker to run guests entirely backed by guest_memfd, even for non-CoCo VMs [1]. This provides a unified memory management model and simplifies guest memory handling. * Direct map removal for enhanced security: This is an important step for direct map removal of guest memory [2]. By allowing host userspace to fault in guest_memfd pages directly, we can avoid maintaining host kernel direct maps of guest memory. This provides additional hardening against Spectre-like transient execution attacks by removing a potential attack surface within the kernel. * Future guest_memfd features: This also lays the groundwork for future enhancements to guest_memfd, such as supporting huge pages and enabling in-place sharing of guest memory with the host for CoCo platforms that permit it [3]. Enable the basic mmap and fault handling logic within guest_memfd, but hold off on allow userspace to actually do mmap() until the architecture support is also in place. [1] https://github.com/firecracker-microvm/firecracker/tree/feature/secret-hiding [2] https://lore.kernel.org/linux-mm/cc1bb8e9bc3e1ab637700a4d3defeec95b55060a.camel@amazon.com [3] https://lore.kernel.org/all/c1c9591d-218a-495c-957b-ba356c8f8e09@redhat.com/T/#u Reviewed-by: Gavin Shan Reviewed-by: Shivank Garg Acked-by: David Hildenbrand Co-developed-by: Ackerley Tng Signed-off-by: Ackerley Tng Signed-off-by: Fuad Tabba --- arch/x86/kvm/x86.c | 11 +++++++ include/linux/kvm_host.h | 4 +++ virt/kvm/guest_memfd.c | 70 ++++++++++++++++++++++++++++++++++++++++ 3 files changed, 85 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a1c49bc681c4..e5cd54ba1eaa 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -13518,6 +13518,16 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu) } EXPORT_SYMBOL_GPL(kvm_arch_no_poll); +#ifdef CONFIG_KVM_GUEST_MEMFD +/* + * KVM doesn't yet support mmap() on guest_memfd for VMs with private memory + * (the private vs. shared tracking needs to be moved into guest_memfd). + */ +bool kvm_arch_supports_gmem_mmap(struct kvm *kvm) +{ + return !kvm_arch_has_private_mem(kvm); +} + #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE int kvm_arch_gmem_prepare(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, int max_order) { @@ -13531,6 +13541,7 @@ void kvm_arch_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end) kvm_x86_call(gmem_invalidate)(start, end); } #endif +#endif int kvm_spec_ctrl_test_value(u64 value) { diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 4d1c44622056..26bad600f9fa 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -726,6 +726,10 @@ static inline bool kvm_arch_has_private_mem(struct kvm *kvm) } #endif +#ifdef CONFIG_KVM_GUEST_MEMFD +bool kvm_arch_supports_gmem_mmap(struct kvm *kvm); +#endif + #ifndef kvm_arch_has_readonly_mem static inline bool kvm_arch_has_readonly_mem(struct kvm *kvm) { diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index a99e11b8b77f..67e7cd7210ef 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -312,7 +312,72 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn) return gfn - slot->base_gfn + slot->gmem.pgoff; } +static bool kvm_gmem_supports_mmap(struct inode *inode) +{ + return false; +} + +static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf) +{ + struct inode *inode = file_inode(vmf->vma->vm_file); + struct folio *folio; + vm_fault_t ret = VM_FAULT_LOCKED; + + if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode)) + return VM_FAULT_SIGBUS; + + folio = kvm_gmem_get_folio(inode, vmf->pgoff); + if (IS_ERR(folio)) { + int err = PTR_ERR(folio); + + if (err == -EAGAIN) + return VM_FAULT_RETRY; + + return vmf_error(err); + } + + if (WARN_ON_ONCE(folio_test_large(folio))) { + ret = VM_FAULT_SIGBUS; + goto out_folio; + } + + if (!folio_test_uptodate(folio)) { + clear_highpage(folio_page(folio, 0)); + kvm_gmem_mark_prepared(folio); + } + + vmf->page = folio_file_page(folio, vmf->pgoff); + +out_folio: + if (ret != VM_FAULT_LOCKED) { + folio_unlock(folio); + folio_put(folio); + } + + return ret; +} + +static const struct vm_operations_struct kvm_gmem_vm_ops = { + .fault = kvm_gmem_fault_user_mapping, +}; + +static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *vma) +{ + if (!kvm_gmem_supports_mmap(file_inode(file))) + return -ENODEV; + + if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) != + (VM_SHARED | VM_MAYSHARE)) { + return -EINVAL; + } + + vma->vm_ops = &kvm_gmem_vm_ops; + + return 0; +} + static struct file_operations kvm_gmem_fops = { + .mmap = kvm_gmem_mmap, .open = generic_file_open, .release = kvm_gmem_release, .fallocate = kvm_gmem_fallocate, @@ -391,6 +456,11 @@ static const struct inode_operations kvm_gmem_iops = { .setattr = kvm_gmem_setattr, }; +bool __weak kvm_arch_supports_gmem_mmap(struct kvm *kvm) +{ + return true; +} + static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) { const char *anon_name = "[kvm-gmem]"; -- 2.50.1.470.g6ba607880d-goog