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Thu, 28 Aug 2025 15:31:03 +0000 (UTC) X-Farcaster-Flow-ID: 47185e85-e09d-469f-9c87-24af2c61ec23 Received: from EX19D022EUC002.ant.amazon.com (10.252.51.137) by EX19MTAEUC001.ant.amazon.com (10.252.51.155) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.17; Thu, 28 Aug 2025 15:31:01 +0000 Received: from EX19D022EUC002.ant.amazon.com (10.252.51.137) by EX19D022EUC002.ant.amazon.com (10.252.51.137) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.17; Thu, 28 Aug 2025 15:31:01 +0000 Received: from EX19D022EUC002.ant.amazon.com ([fe80::bd:307b:4d3a:7d80]) by EX19D022EUC002.ant.amazon.com ([fe80::bd:307b:4d3a:7d80%3]) with mapi id 15.02.2562.017; Thu, 28 Aug 2025 15:31:01 +0000 From: "Kalyazin, Nikita" To: "pbonzini@redhat.com" , "shuah@kernel.org" CC: "kvm@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "michael.day@amd.com" , "david@redhat.com" , "jthoughton@google.com" , "Roy, Patrick" , "Thomson, Jack" , "Manwaring, Derek" , "Cali, Marco" , "Kalyazin, Nikita" Subject: [PATCH v4 1/2] KVM: guest_memfd: add generic population via write Thread-Topic: [PATCH v4 1/2] KVM: guest_memfd: add generic population via write Thread-Index: AQHcGDDCvFtEUrPBRUaVWhkWmm3z+g== Date: Thu, 28 Aug 2025 15:31:01 +0000 Message-ID: <20250828153049.3922-2-kalyazin@amazon.com> References: <20250828153049.3922-1-kalyazin@amazon.com> In-Reply-To: <20250828153049.3922-1-kalyazin@amazon.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 write syscall populates guest_memfd with user-supplied data in a generic=0A= way, ie no vendor-specific preparation is performed. This is supposed=0A= to be used in non-CoCo setups where guest memory is not=0A= hardware-encrypted.=0A= =0A= The following behaviour is implemented:=0A= - only page-aligned count and offset are allowed=0A= - if the memory is already allocated, the call will successfully=0A= populate it=0A= - if the memory is not allocated, the call will both allocate and=0A= populate=0A= - if the memory is already populated, the call will not repopulate it=0A= =0A= Signed-off-by: Nikita Kalyazin =0A= ---=0A= virt/kvm/guest_memfd.c | 64 +++++++++++++++++++++++++++++++++++++++++-=0A= 1 file changed, 63 insertions(+), 1 deletion(-)=0A= =0A= diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c=0A= index 08a6bc7d25b6..1f6f85edace0 100644=0A= --- a/virt/kvm/guest_memfd.c=0A= +++ b/virt/kvm/guest_memfd.c=0A= @@ -379,7 +379,9 @@ static int kvm_gmem_mmap(struct file *file, struct vm_a= rea_struct *vma)=0A= }=0A= =0A= static struct file_operations kvm_gmem_fops =3D {=0A= - .mmap =3D kvm_gmem_mmap,=0A= + .mmap =3D kvm_gmem_mmap,=0A= + .llseek =3D default_llseek,=0A= + .write_iter =3D generic_perform_write,=0A= .open =3D generic_file_open,=0A= .release =3D kvm_gmem_release,=0A= .fallocate =3D kvm_gmem_fallocate,=0A= @@ -390,6 +392,63 @@ void kvm_gmem_init(struct module *module)=0A= kvm_gmem_fops.owner =3D module;=0A= }=0A= =0A= +static int kvm_kmem_gmem_write_begin(const struct kiocb *kiocb,=0A= + struct address_space *mapping,=0A= + loff_t pos, unsigned len,=0A= + struct folio **foliop,=0A= + void **fsdata)=0A= +{=0A= + struct file *file =3D kiocb->ki_filp;=0A= + pgoff_t index =3D pos >> PAGE_SHIFT;=0A= + struct folio *folio;=0A= +=0A= + if (!PAGE_ALIGNED(pos) || len !=3D PAGE_SIZE)=0A= + return -EINVAL;=0A= +=0A= + if (pos + len > i_size_read(file_inode(file)))=0A= + return -EINVAL;=0A= +=0A= + folio =3D kvm_gmem_get_folio(file_inode(file), index);=0A= + if (IS_ERR(folio))=0A= + return -EFAULT;=0A= +=0A= + if (WARN_ON_ONCE(folio_test_large(folio))) {=0A= + folio_unlock(folio);=0A= + folio_put(folio);=0A= + return -EFAULT;=0A= + }=0A= +=0A= + if (folio_test_uptodate(folio)) {=0A= + folio_unlock(folio);=0A= + folio_put(folio);=0A= + return -ENOSPC;=0A= + }=0A= +=0A= + *foliop =3D folio;=0A= + return 0;=0A= +}=0A= +=0A= +static int kvm_kmem_gmem_write_end(const struct kiocb *kiocb,=0A= + struct address_space *mapping,=0A= + loff_t pos, unsigned len, unsigned copied,=0A= + struct folio *folio, void *fsdata)=0A= +{=0A= + int ret;=0A= +=0A= + if (copied =3D=3D len) {=0A= + kvm_gmem_mark_prepared(folio);=0A= + ret =3D copied;=0A= + } else {=0A= + filemap_remove_folio(folio);=0A= + ret =3D 0;=0A= + }=0A= +=0A= + folio_unlock(folio);=0A= + folio_put(folio);=0A= +=0A= + return ret;=0A= +}=0A= +=0A= static int kvm_gmem_migrate_folio(struct address_space *mapping,=0A= struct folio *dst, struct folio *src,=0A= enum migrate_mode mode)=0A= @@ -442,6 +501,8 @@ static void kvm_gmem_free_folio(struct folio *folio)=0A= =0A= static const struct address_space_operations kvm_gmem_aops =3D {=0A= .dirty_folio =3D noop_dirty_folio,=0A= + .write_begin =3D kvm_kmem_gmem_write_begin,=0A= + .write_end =3D kvm_kmem_gmem_write_end,=0A= .migrate_folio =3D kvm_gmem_migrate_folio,=0A= .error_remove_folio =3D kvm_gmem_error_folio,=0A= #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_INVALIDATE=0A= @@ -489,6 +550,7 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t si= ze, u64 flags)=0A= }=0A= =0A= file->f_flags |=3D O_LARGEFILE;=0A= + file->f_mode |=3D FMODE_LSEEK | FMODE_PWRITE;=0A= =0A= inode =3D file->f_inode;=0A= WARN_ON(file->f_mapping !=3D inode->i_mapping);=0A= -- =0A= 2.50.1=0A= =0A=