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AJvYcCVT5jrRjm1XZlEnZ46zPfEDH6yiNJ/Bvrwgybm9SBpFcj6NJSzHGidxAUweJe7L72VHdszeExYN1Q==@kvack.org X-Gm-Message-State: AOJu0YzsiWw6Bcyj6Qx/i024MIosEyCo5WPbtyb0H6zcyiTw1FmMcw8+ ECU0j3+ik3OQip7uwm8zy7HW6GEy+aPtpoRAJfQFhXHHh6ZEmw/4e8xHN6ZcErV6El/l0BFtUFY VlHTjFYhWjJsB91jH0Kn8SA== X-Google-Smtp-Source: AGHT+IE1r4rRbCGThMYXNJtfRCWTqW4iO0Aq7HgjWX2EnvsJvHx+lTepMEw90l9uu9sJTWAqTJV2AhsdFxGMQQEIAw== X-Received: from pfnx2.prod.google.com ([2002:aa7:84c2:0:b0:736:451f:b9f4]) (user=ackerleytng job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:1397:b0:736:35d4:f03f with SMTP id d2e1a72fcca58-73980387936mr27344709b3a.6.1743635035386; Wed, 02 Apr 2025 16:03:55 -0700 (PDT) Date: Wed, 02 Apr 2025 16:03:53 -0700 In-Reply-To: <20250328153133.3504118-8-tabba@google.com> (message from Fuad Tabba on Fri, 28 Mar 2025 15:31:33 +0000) Mime-Version: 1.0 Message-ID: Subject: Re: [PATCH v7 7/7] KVM: guest_memfd: Add a guest_memfd() flag to initialize it as shared From: Ackerley Tng To: Fuad Tabba 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, tabba@google.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: B28461C000F X-Stat-Signature: c914kdum1mjnzxuf9mmcr9caa7p8ec7e X-Rspam-User: X-HE-Tag: 1743635036-598966 X-HE-Meta: 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 WH/6lAw+ 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 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: 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/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); I think if GUEST_MEMFD_FLAG_INIT_SHARED is not set, we should call kvm_gmem_offset_range_clear_shared(); so that there is always some shareability defined for all offsets in a file. Otherwise, when reading shareability, we'd have to check against GUEST_MEMFD_FLAG_INIT_SHARED to find out what to initialize it to. > + 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;