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Fri, 04 Apr 2025 00:40:35 -0700 (PDT) MIME-Version: 1.0 References: <20250328153133.3504118-8-tabba@google.com> In-Reply-To: From: Fuad Tabba Date: Fri, 4 Apr 2025 08:39:58 +0100 X-Gm-Features: ATxdqUES1GQahg7fTolYInex80Nv9poFQfIEx56A1_oFSbplzfZGtv-MWgV4DME Message-ID: Subject: Re: [PATCH v7 7/7] KVM: guest_memfd: Add a guest_memfd() flag to initialize it as shared To: Ackerley Tng Cc: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, 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, 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 Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 86A90C000B X-Stat-Signature: xqar7rzxfi5i1xc3ao5t964wbqq1ckna X-Rspam-User: X-HE-Tag: 1743752436-869983 X-HE-Meta: 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 NHwn4aeo ygPYjRqJYjdfIPCCPq2UYxr0tKrk6NRXh/TvmKHGgYZSt/eLuOiczzCunMDUn4VLX/ohx3U3dR+4fspNjqA5TrWSw1c+frxEHsa0j8ZA/JebONU3BtRZC5clqBkk4lm0FX2+iRSjANf0DE4p/k/ktOtxTHpTBrLHZ4CBTeSOLZMYYTauLBbIPNZEGDHwwL7ZkRf4a4Fut8a7tkj8WBu8us1xzpyYv8508YzgLmHBL1OwUzfqyXuUC1qjAS4QsvJJYDkDdAEgh/61FxNbrK0/J8ODaPyVLEFpL0K9rP0+3Q01U696FVVRsNcZ+Jjxzb8qxUW3ng0uhx8uWoFMeYRJv295KNoBpenrnLJsufxviMzaPeK0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Ackerley, On Wed, 2 Apr 2025 at 23:47, Ackerley Tng wrote: > > Fuad Tabba writes: > > > Not all use cases require guest_memfd() to be shared with the host when > > first created. Add a new flag, GUEST_MEMFD_FLAG_INIT_SHARED, which when > > set on KVM_CREATE_GUEST_MEMFD initializes the memory as shared with the > > host, and therefore mappable by it. Otherwise, memory is private until > > explicitly shared by the guest with the host. > > > > Signed-off-by: Fuad Tabba > > --- > > Documentation/virt/kvm/api.rst | 4 ++++ > > include/uapi/linux/kvm.h | 1 + > > tools/testing/selftests/kvm/guest_memfd_test.c | 7 +++++-- > > virt/kvm/guest_memfd.c | 12 ++++++++++++ > > 4 files changed, 22 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > > index 2b52eb77e29c..a5496d7d323b 100644 > > --- a/Documentation/virt/kvm/api.rst > > +++ b/Documentation/virt/kvm/api.rst > > @@ -6386,6 +6386,10 @@ most one mapping per page, i.e. binding multiple memory regions to a single > > guest_memfd range is not allowed (any number of memory regions can be bound to > > a single guest_memfd file, but the bound ranges must not overlap). > > > > +If the capability KVM_CAP_GMEM_SHARED_MEM is supported, then the flags field > > +supports GUEST_MEMFD_FLAG_INIT_SHARED, which initializes the memory as shared > > +with the host, and thereby, mappable by it. > > + > > See KVM_SET_USER_MEMORY_REGION2 for additional details. > > > > 4.143 KVM_PRE_FAULT_MEMORY > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > > index 117937a895da..22d7e33bf09c 100644 > > --- a/include/uapi/linux/kvm.h > > +++ b/include/uapi/linux/kvm.h > > @@ -1566,6 +1566,7 @@ struct kvm_memory_attributes { > > #define KVM_MEMORY_ATTRIBUTE_PRIVATE (1ULL << 3) > > > > #define KVM_CREATE_GUEST_MEMFD _IOWR(KVMIO, 0xd4, struct kvm_create_guest_memfd) > > +#define GUEST_MEMFD_FLAG_INIT_SHARED (1UL << 0) > > > > struct kvm_create_guest_memfd { > > __u64 size; > > diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c > > index 38c501e49e0e..4a7fcd6aa372 100644 > > --- a/tools/testing/selftests/kvm/guest_memfd_test.c > > +++ b/tools/testing/selftests/kvm/guest_memfd_test.c > > @@ -159,7 +159,7 @@ static void test_invalid_punch_hole(int fd, size_t page_size, size_t total_size) > > static void test_create_guest_memfd_invalid(struct kvm_vm *vm) > > { > > size_t page_size = getpagesize(); > > - uint64_t flag; > > + uint64_t flag = BIT(0); > > size_t size; > > int fd; > > > > @@ -170,7 +170,10 @@ static void test_create_guest_memfd_invalid(struct kvm_vm *vm) > > size); > > } > > > > - for (flag = BIT(0); flag; flag <<= 1) { > > + if (kvm_has_cap(KVM_CAP_GMEM_SHARED_MEM)) > > + flag = GUEST_MEMFD_FLAG_INIT_SHARED << 1; > > + > > + for (; flag; flag <<= 1) { > > This would end up shifting the GUEST_MEMFD_FLAG_INIT_SHARED flag for > each loop. Yes. That's my intention. This tests whether the flags are invalid. Without GUEST_MEMFD_FLAG_INIT_SHARED, no flag is valid, so it starts with bit zero and goes through all the flags. If KVM_CAP_GMEM_SHARED_MEM is available, then we want to start from bit 1 (i.e., skip bit 0, which is GUEST_MEMFD_FLAG_INIT_SHARED). Cheers, /fuad > > fd = __vm_create_guest_memfd(vm, page_size, flag); > > TEST_ASSERT(fd == -1 && errno == EINVAL, > > "guest_memfd() with flag '0x%lx' should fail with EINVAL", > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > > index eec9d5e09f09..32e149478b04 100644 > > --- a/virt/kvm/guest_memfd.c > > +++ b/virt/kvm/guest_memfd.c > > @@ -1069,6 +1069,15 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) > > goto err_gmem; > > } > > > > + if (IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM) && > > + (flags & GUEST_MEMFD_FLAG_INIT_SHARED)) { > > + err = kvm_gmem_offset_range_set_shared(file_inode(file), 0, size >> PAGE_SHIFT); > > + if (err) { > > + fput(file); > > + goto err_gmem; > > + } > > + } > > + > > kvm_get_kvm(kvm); > > gmem->kvm = kvm; > > xa_init(&gmem->bindings); > > @@ -1090,6 +1099,9 @@ int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args) > > u64 flags = args->flags; > > u64 valid_flags = 0; > > > > + if (IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM)) > > + valid_flags |= GUEST_MEMFD_FLAG_INIT_SHARED; > > + > > if (flags & ~valid_flags) > > return -EINVAL;