From nobody Sun Oct 5 21:42:51 2025 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (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 93FBD2BE7AA for ; Tue, 29 Jul 2025 22:55:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753829749; cv=none; b=lONtmjycxkRG6dSlchS/ibVOl14p9auKvxNjQFH0gjU+YAEy/qUmUbyhwknm54If9Qd7ZV9e8Pgiv4NTeFI0BEcGnb1xx7RJmkFPfKr+QMWbuqgb7dEjh3ZLL8xLQOK6u6TKQLNmN/Py4YL4nOTg/hCNb9UvEnEUmTd4UOoa9LM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753829749; c=relaxed/simple; bh=Xbe974jAg04TIW9HfK3Y4I+nikYFzuKAbkXN+KFWFPw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=n78wbaglQbmX3LLCNnSGUXEWZmW0CzoHHRMrBFGhfZfba9Wy4jT6V00L/WoQxAXO1Mo7xcaTWJ8MZDa+LQAY7yB+BBldfAAkzM/sDwFbpbbExMAjonNH+VbX6LhXua4JuBBLRljHXWkUkVLVKGkLea8HhBPWSkLf2LgSGVzk7N0= 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=qw/IIqlV; arc=none smtp.client-ip=209.85.214.201 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="qw/IIqlV" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-237e6963f70so105911865ad.2 for ; Tue, 29 Jul 2025 15:55:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1753829747; x=1754434547; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=tn1mSBLO+YLVwstEyyon9JR/mQU0lWjJcGUdOXFvVvs=; b=qw/IIqlVlsHtwrrpV317Ga6/K1j02MpDgvhCP9CenNVJ1OH6SwpLhbJgPl+LbtafLE OKuQUOFqPc9wzLjIbBKEvcBX4bT8M3e+KMw+LYWyyAFJj3fwyh9LlVQgLq0NOBBMppIA lOCHUobchVa38CMjb/lKZQ7eUmbBEzU+JS29rlTeA+udEdvyZhqXDei8W0LtBH/Bv8KR B90ZqKtMhuapcKZ+eYwCiEhg7vzeFaPV3rNcS+7iuD+AT/8/ZWY6ZAMu+OqYQ1aFSEhU /Vwm3Cjuj4DgTpF5FvsjAmxLGRUMo5Xp8Uc6rQtzxGQoEZ5n02DrxVLaDslXJw1iEtGV qg9w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1753829747; x=1754434547; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=tn1mSBLO+YLVwstEyyon9JR/mQU0lWjJcGUdOXFvVvs=; b=hLNpVjkn4Q6/6MFXncwWFbdo3Y7zlxLQLAzJ9hgD5RuA9HHFSlCbUw5vIaxCOm4zIa R35SlmTHcnHmfJnpm3gtgy6VL2ZHnuDnu7FHgIsyfMjalOmWmssbS9g25WJpnlHHLQXs 16m9qliPFIQYHK+bJFIdvMYaJfArdxeAPl7X7hgHm98SaXRYcCpRd5JrhLuG6EyYiB4T 2c6RMJt9qXlLfznEC3pHvSrY9dYckvcxs9jVv9SL6/y9wDCc97E2WeWpBStLtAJTnD41 3eb1Wvhf/Zii7QinsCa8IQvGVT3Xo0XNftvkXC3JPaBGXdYlK0T0NyF0J+1aTh7pbY2r rhJA== X-Forwarded-Encrypted: i=1; AJvYcCXor4O4G1+68eH1UvhJFQCjHTpt9cChtEesyChD6xmA/b1YrIVVj/ChZcGRoXxQ64Rrhh1Cki9b9uxKm0o=@vger.kernel.org X-Gm-Message-State: AOJu0YwIbOqM1tTFQPlIpPdlgNrw9uSN1AkV31+ke6pngihPbV3pULSO YRS9T5Z9WkmimemXY78+kWCVeknTi9yTZ0bWGEeRTc+neY8VkbkbI6c+T9CJwkHlHkIIy5wHToI 60iO7jw== X-Google-Smtp-Source: AGHT+IHAFJZIedsHoBlxMRk1Os6nimsUyZRbs4o25k9lGhNMmtWWfdhx2zaS8kMkKKU+mHoV57Vx/+pszAo= X-Received: from pjk4.prod.google.com ([2002:a17:90b:5584:b0:312:187d:382d]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:d505:b0:240:6740:6b11 with SMTP id d9443c01a7336-24096b0faa3mr13034795ad.40.1753829746789; Tue, 29 Jul 2025 15:55:46 -0700 (PDT) Reply-To: Sean Christopherson Date: Tue, 29 Jul 2025 15:54:41 -0700 In-Reply-To: <20250729225455.670324-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250729225455.670324-1-seanjc@google.com> X-Mailer: git-send-email 2.50.1.552.g942d659e1b-goog Message-ID: <20250729225455.670324-11-seanjc@google.com> Subject: [PATCH v17 10/24] KVM: guest_memfd: Add plumbing to host to map guest_memfd pages From: Sean Christopherson To: Paolo Bonzini , Marc Zyngier , Oliver Upton , Sean Christopherson Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, Ira Weiny , Gavin Shan , Shivank Garg , Vlastimil Babka , Xiaoyao Li , David Hildenbrand , Fuad Tabba , Ackerley Tng , Tao Chan , James Houghton Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Fuad Tabba 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/cc1bb8e9bc3e1ab637700a4d3defeec95b5506= 0a.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 Reviewed-by: Xiaoyao Li Signed-off-by: Sean Christopherson --- 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); =20 +#ifdef CONFIG_KVM_GUEST_MEMFD +/* + * KVM doesn't yet support mmap() on guest_memfd for VMs with private memo= ry + * (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 m= ax_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 =20 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 =20 +#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_sl= ot *slot, gfn_t gfn) return gfn - slot->base_gfn + slot->gmem.pgoff; } =20 +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 =3D file_inode(vmf->vma->vm_file); + struct folio *folio; + vm_fault_t ret =3D VM_FAULT_LOCKED; + + if (((loff_t)vmf->pgoff << PAGE_SHIFT) >=3D i_size_read(inode)) + return VM_FAULT_SIGBUS; + + folio =3D kvm_gmem_get_folio(inode, vmf->pgoff); + if (IS_ERR(folio)) { + int err =3D PTR_ERR(folio); + + if (err =3D=3D -EAGAIN) + return VM_FAULT_RETRY; + + return vmf_error(err); + } + + if (WARN_ON_ONCE(folio_test_large(folio))) { + ret =3D VM_FAULT_SIGBUS; + goto out_folio; + } + + if (!folio_test_uptodate(folio)) { + clear_highpage(folio_page(folio, 0)); + kvm_gmem_mark_prepared(folio); + } + + vmf->page =3D folio_file_page(folio, vmf->pgoff); + +out_folio: + if (ret !=3D VM_FAULT_LOCKED) { + folio_unlock(folio); + folio_put(folio); + } + + return ret; +} + +static const struct vm_operations_struct kvm_gmem_vm_ops =3D { + .fault =3D 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)) !=3D + (VM_SHARED | VM_MAYSHARE)) { + return -EINVAL; + } + + vma->vm_ops =3D &kvm_gmem_vm_ops; + + return 0; +} + static struct file_operations kvm_gmem_fops =3D { + .mmap =3D kvm_gmem_mmap, .open =3D generic_file_open, .release =3D kvm_gmem_release, .fallocate =3D kvm_gmem_fallocate, @@ -391,6 +456,11 @@ static const struct inode_operations kvm_gmem_iops =3D= { .setattr =3D kvm_gmem_setattr, }; =20 +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 =3D "[kvm-gmem]"; --=20 2.50.1.552.g942d659e1b-goog