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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 3EB2AC000A X-Stat-Signature: wkqwnf8j1jozmtcqhc5faps6dq1h38go X-Rspam-User: X-HE-Tag: 1773756755-877817 X-HE-Meta: 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 oZmwkf6C 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Patrick Roy =0A= =0A= Add GUEST_MEMFD_FLAG_NO_DIRECT_MAP flag for KVM_CREATE_GUEST_MEMFD()=0A= ioctl. When set, guest_memfd folios will be removed from the direct map=0A= after preparation, with direct map entries only restored when the folios=0A= are freed.=0A= =0A= To ensure these folios do not end up in places where the kernel cannot=0A= deal with them, set AS_NO_DIRECT_MAP on the guest_memfd's struct=0A= address_space if GUEST_MEMFD_FLAG_NO_DIRECT_MAP is requested.=0A= =0A= Note that this flag causes removal of direct map entries for all=0A= guest_memfd folios independent of whether they are "shared" or "private"=0A= (although current guest_memfd only supports either all folios in the=0A= "shared" state, or all folios in the "private" state if=0A= GUEST_MEMFD_FLAG_MMAP is not set). The usecase for removing direct map=0A= entries of also the shared parts of guest_memfd are a special type of=0A= non-CoCo VM where, host userspace is trusted to have access to all of=0A= guest memory, but where Spectre-style transient execution attacks=0A= through the host kernel's direct map should still be mitigated. In this=0A= setup, KVM retains access to guest memory via userspace mappings of=0A= guest_memfd, which are reflected back into KVM's memslots via=0A= userspace_addr. This is needed for things like MMIO emulation on x86_64=0A= to work.=0A= =0A= Direct map entries are zapped right before guest or userspace mappings=0A= of gmem folios are set up, e.g. in kvm_gmem_fault_user_mapping() or=0A= kvm_gmem_get_pfn() [called from the KVM MMU code]. The only place where=0A= a gmem folio can be allocated without being mapped anywhere is=0A= kvm_gmem_populate(), where handling potential failures of direct map=0A= removal is not possible (by the time direct map removal is attempted,=0A= the folio is already marked as prepared, meaning attempting to re-try=0A= kvm_gmem_populate() would just result in -EEXIST without fixing up the=0A= direct map state). These folios are then removed form the direct map=0A= upon kvm_gmem_get_pfn(), e.g. when they are mapped into the guest later.=0A= =0A= Signed-off-by: Patrick Roy =0A= Signed-off-by: Nikita Kalyazin =0A= ---=0A= Documentation/virt/kvm/api.rst | 21 ++++++-----=0A= include/linux/kvm_host.h | 3 ++=0A= include/uapi/linux/kvm.h | 1 +=0A= virt/kvm/guest_memfd.c | 67 ++++++++++++++++++++++++++++++++--=0A= 4 files changed, 79 insertions(+), 13 deletions(-)=0A= =0A= diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rs= t=0A= index 032516783e96..8feec77b03fe 100644=0A= --- a/Documentation/virt/kvm/api.rst=0A= +++ b/Documentation/virt/kvm/api.rst=0A= @@ -6439,15 +6439,18 @@ a single guest_memfd file, but the bound ranges mus= t not overlap).=0A= The capability KVM_CAP_GUEST_MEMFD_FLAGS enumerates the `flags` that can b= e=0A= specified via KVM_CREATE_GUEST_MEMFD. Currently defined flags:=0A= =0A= - =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=0A= - GUEST_MEMFD_FLAG_MMAP Enable using mmap() on the guest_memfd file= =0A= - descriptor.=0A= - GUEST_MEMFD_FLAG_INIT_SHARED Make all memory in the file shared during= =0A= - KVM_CREATE_GUEST_MEMFD (memory files create= d=0A= - without INIT_SHARED will be marked private)= .=0A= - Shared memory can be faulted into host user= space=0A= - page tables. Private memory cannot.=0A= - =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=0A= + =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=0A= + GUEST_MEMFD_FLAG_MMAP Enable using mmap() on the guest_memfd fi= le=0A= + descriptor.=0A= + GUEST_MEMFD_FLAG_INIT_SHARED Make all memory in the file shared during= =0A= + KVM_CREATE_GUEST_MEMFD (memory files crea= ted=0A= + without INIT_SHARED will be marked privat= e).=0A= + Shared memory can be faulted into host us= erspace=0A= + page tables. Private memory cannot.=0A= + GUEST_MEMFD_FLAG_NO_DIRECT_MAP The guest_memfd instance will unmap the m= emory=0A= + backing it from the kernel's address spac= e=0A= + before passing it off to userspace or the= guest.=0A= + =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=0A= =0A= When the KVM MMU performs a PFN lookup to service a guest fault and the ba= cking=0A= guest_memfd has the GUEST_MEMFD_FLAG_MMAP set, then the fault will always = be=0A= diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h=0A= index ce8c5fdf2752..c95747e2278c 100644=0A= --- a/include/linux/kvm_host.h=0A= +++ b/include/linux/kvm_host.h=0A= @@ -738,6 +738,9 @@ static inline u64 kvm_gmem_get_supported_flags(struct k= vm *kvm)=0A= if (!kvm || kvm_arch_supports_gmem_init_shared(kvm))=0A= flags |=3D GUEST_MEMFD_FLAG_INIT_SHARED;=0A= =0A= + if (!kvm || kvm_arch_gmem_supports_no_direct_map(kvm))=0A= + flags |=3D GUEST_MEMFD_FLAG_NO_DIRECT_MAP;=0A= +=0A= return flags;=0A= }=0A= #endif=0A= diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h=0A= index 80364d4dbebb..d864f67efdb7 100644=0A= --- a/include/uapi/linux/kvm.h=0A= +++ b/include/uapi/linux/kvm.h=0A= @@ -1642,6 +1642,7 @@ struct kvm_memory_attributes {=0A= #define KVM_CREATE_GUEST_MEMFD _IOWR(KVMIO, 0xd4, struct kvm_create_guest= _memfd)=0A= #define GUEST_MEMFD_FLAG_MMAP (1ULL << 0)=0A= #define GUEST_MEMFD_FLAG_INIT_SHARED (1ULL << 1)=0A= +#define GUEST_MEMFD_FLAG_NO_DIRECT_MAP (1ULL << 2)=0A= =0A= struct kvm_create_guest_memfd {=0A= __u64 size;=0A= diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c=0A= index 651649623448..c9344647579c 100644=0A= --- a/virt/kvm/guest_memfd.c=0A= +++ b/virt/kvm/guest_memfd.c=0A= @@ -7,6 +7,7 @@=0A= #include =0A= #include =0A= #include =0A= +#include =0A= =0A= #include "kvm_mm.h"=0A= =0A= @@ -76,6 +77,35 @@ static int __kvm_gmem_prepare_folio(struct kvm *kvm, str= uct kvm_memory_slot *slo=0A= return 0;=0A= }=0A= =0A= +#define KVM_GMEM_FOLIO_NO_DIRECT_MAP BIT(0)=0A= +=0A= +static bool kvm_gmem_folio_no_direct_map(struct folio *folio)=0A= +{=0A= + return ((u64)folio->private) & KVM_GMEM_FOLIO_NO_DIRECT_MAP;=0A= +}=0A= +=0A= +static int kvm_gmem_folio_zap_direct_map(struct folio *folio)=0A= +{=0A= + u64 gmem_flags =3D GMEM_I(folio_inode(folio))->flags;=0A= + int r =3D 0;=0A= +=0A= + if (kvm_gmem_folio_no_direct_map(folio) || !(gmem_flags & GUEST_MEMFD_FLA= G_NO_DIRECT_MAP))=0A= + goto out;=0A= +=0A= + r =3D folio_zap_direct_map(folio);=0A= + if (!r)=0A= + folio->private =3D (void *)((u64)folio->private | KVM_GMEM_FOLIO_NO_DIRE= CT_MAP);=0A= +=0A= +out:=0A= + return r;=0A= +}=0A= +=0A= +static void kvm_gmem_folio_restore_direct_map(struct folio *folio)=0A= +{=0A= + folio_restore_direct_map(folio);=0A= + folio->private =3D (void *)((u64)folio->private & ~KVM_GMEM_FOLIO_NO_DIRE= CT_MAP);=0A= +}=0A= +=0A= /*=0A= * Process @folio, which contains @gfn, so that the guest can use it.=0A= * The folio must be locked and the gfn must be contained in @slot.=0A= @@ -388,11 +418,17 @@ static bool kvm_gmem_supports_mmap(struct inode *inod= e)=0A= return GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_MMAP;=0A= }=0A= =0A= +static bool kvm_gmem_no_direct_map(struct inode *inode)=0A= +{=0A= + return GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_NO_DIRECT_MAP;=0A= +}=0A= +=0A= static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf)=0A= {=0A= struct inode *inode =3D file_inode(vmf->vma->vm_file);=0A= struct folio *folio;=0A= vm_fault_t ret =3D VM_FAULT_LOCKED;=0A= + int err;=0A= =0A= if (((loff_t)vmf->pgoff << PAGE_SHIFT) >=3D i_size_read(inode))=0A= return VM_FAULT_SIGBUS;=0A= @@ -418,6 +454,14 @@ static vm_fault_t kvm_gmem_fault_user_mapping(struct v= m_fault *vmf)=0A= folio_mark_uptodate(folio);=0A= }=0A= =0A= + if (kvm_gmem_no_direct_map(folio_inode(folio))) {=0A= + err =3D kvm_gmem_folio_zap_direct_map(folio);=0A= + if (err) {=0A= + ret =3D vmf_error(err);=0A= + goto out_folio;=0A= + }=0A= + }=0A= +=0A= vmf->page =3D folio_file_page(folio, vmf->pgoff);=0A= =0A= out_folio:=0A= @@ -528,6 +572,9 @@ static void kvm_gmem_free_folio(struct folio *folio)=0A= kvm_pfn_t pfn =3D page_to_pfn(page);=0A= int order =3D folio_order(folio);=0A= =0A= + if (kvm_gmem_folio_no_direct_map(folio))=0A= + kvm_gmem_folio_restore_direct_map(folio);=0A= +=0A= kvm_arch_gmem_invalidate(pfn, pfn + (1ul << order));=0A= }=0A= =0A= @@ -591,6 +638,9 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t si= ze, u64 flags)=0A= /* Unmovable mappings are supposed to be marked unevictable as well. */= =0A= WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));=0A= =0A= + if (flags & GUEST_MEMFD_FLAG_NO_DIRECT_MAP)=0A= + mapping_set_no_direct_map(inode->i_mapping);=0A= +=0A= GMEM_I(inode)->flags =3D flags;=0A= =0A= file =3D alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, &kvm_gmem_f= ops);=0A= @@ -803,13 +853,22 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memo= ry_slot *slot,=0A= }=0A= =0A= r =3D kvm_gmem_prepare_folio(kvm, slot, gfn, folio);=0A= + if (r)=0A= + goto out_unlock;=0A= =0A= + if (kvm_gmem_no_direct_map(folio_inode(folio))) {=0A= + r =3D kvm_gmem_folio_zap_direct_map(folio);=0A= + if (r)=0A= + goto out_unlock;=0A= + }=0A= +=0A= + *page =3D folio_file_page(folio, index);=0A= folio_unlock(folio);=0A= + return 0;=0A= =0A= - if (!r)=0A= - *page =3D folio_file_page(folio, index);=0A= - else=0A= - folio_put(folio);=0A= +out_unlock:=0A= + folio_unlock(folio);=0A= + folio_put(folio);=0A= =0A= return r;=0A= }=0A= -- =0A= 2.50.1=0A= =0A=