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Mon, 20 Oct 2025 16:14:06 +0000 (UTC) X-Farcaster-Flow-ID: a5299e80-435c-40e6-94ce-2de2a320a4cc Received: from EX19D022EUC003.ant.amazon.com (10.252.51.167) by EX19MTAEUB001.ant.amazon.com (10.252.51.28) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.20; Mon, 20 Oct 2025 16:14:05 +0000 Received: from EX19D022EUC002.ant.amazon.com (10.252.51.137) by EX19D022EUC003.ant.amazon.com (10.252.51.167) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.20; Mon, 20 Oct 2025 16:14:05 +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 15.02.2562.020; Mon, 20 Oct 2025 16:14:05 +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" , "seanjc@google.com" , "david@redhat.com" , "jthoughton@google.com" , "patrick.roy@linux.dev" , "Thomson, Jack" , "Manwaring, Derek" , "Cali, Marco" , "Kalyazin, Nikita" Subject: [PATCH v6 1/2] KVM: guest_memfd: add generic population via write Thread-Topic: [PATCH v6 1/2] KVM: guest_memfd: add generic population via write Thread-Index: AQHcQdyOdC7YhcHS8EaGGq7hvFXtwg== Date: Mon, 20 Oct 2025 16:14:05 +0000 Message-ID: <20251020161352.69257-2-kalyazin@amazon.com> References: <20251020161352.69257-1-kalyazin@amazon.com> In-Reply-To: <20251020161352.69257-1-kalyazin@amazon.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: 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 Content-Type: text/plain; charset="utf-8" From: Nikita Kalyazin write syscall populates guest_memfd with user-supplied data in a generic way, ie no vendor-specific preparation is performed. If the request is not page-aligned, the remaining bytes are initialised to 0. write is only supported for non-CoCo setups where guest memory is not hardware-encrypted. Signed-off-by: Nikita Kalyazin --- virt/kvm/guest_memfd.c | 48 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+) diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 94bafd6c558c..f4e218049afa 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -380,6 +380,8 @@ static int kvm_gmem_mmap(struct file *file, struct vm_a= rea_struct *vma) =20 static struct file_operations kvm_gmem_fops =3D { .mmap =3D kvm_gmem_mmap, + .llseek =3D default_llseek, + .write_iter =3D generic_perform_write, .open =3D generic_file_open, .release =3D kvm_gmem_release, .fallocate =3D kvm_gmem_fallocate, @@ -390,6 +392,49 @@ void kvm_gmem_init(struct module *module) kvm_gmem_fops.owner =3D module; } =20 +static int kvm_kmem_gmem_write_begin(const struct kiocb *kiocb, + struct address_space *mapping, + loff_t pos, unsigned int len, + struct folio **foliop, + void **fsdata) +{ + struct file *file =3D kiocb->ki_filp; + struct inode *inode =3D file_inode(file); + pgoff_t index =3D pos >> PAGE_SHIFT; + struct folio *folio; + + if (!kvm_gmem_supports_mmap(inode)) + return -ENODEV; + + if (pos + len > i_size_read(inode)) + return -EINVAL; + + folio =3D kvm_gmem_get_folio(inode, index); + if (IS_ERR(folio)) + return -EFAULT; + + *foliop =3D folio; + return 0; +} + +static int kvm_kmem_gmem_write_end(const struct kiocb *kiocb, + struct address_space *mapping, + loff_t pos, unsigned int len, + unsigned int copied, + struct folio *folio, void *fsdata) +{ + if (copied && copied < len) { + unsigned int from =3D pos & ((1UL << folio_order(folio)) - 1); + + folio_zero_range(folio, from + copied, len - copied); + } + + folio_unlock(folio); + folio_put(folio); + + return copied; +} + static int kvm_gmem_migrate_folio(struct address_space *mapping, struct folio *dst, struct folio *src, enum migrate_mode mode) @@ -442,6 +487,8 @@ static void kvm_gmem_free_folio(struct folio *folio) =20 static const struct address_space_operations kvm_gmem_aops =3D { .dirty_folio =3D noop_dirty_folio, + .write_begin =3D kvm_kmem_gmem_write_begin, + .write_end =3D kvm_kmem_gmem_write_end, .migrate_folio =3D kvm_gmem_migrate_folio, .error_remove_folio =3D kvm_gmem_error_folio, #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_INVALIDATE @@ -489,6 +536,7 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t si= ze, u64 flags) } =20 file->f_flags |=3D O_LARGEFILE; + file->f_mode |=3D FMODE_LSEEK | FMODE_PWRITE; =20 inode =3D file->f_inode; WARN_ON(file->f_mapping !=3D inode->i_mapping); --=20 2.50.1