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Mon, 05 Aug 2024 11:13:01 -0700 (PDT) MIME-Version: 1.0 References: <20240801090117.3841080-5-tabba@google.com> In-Reply-To: From: Fuad Tabba Date: Mon, 5 Aug 2024 19:12:24 +0100 Message-ID: Subject: Re: [RFC PATCH v2 04/10] KVM: Add KVM capability to check if guest_memfd can be mapped by the host 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, yu.c.zhang@linux.intel.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 Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Stat-Signature: tj5qpzoc3tor7n8wydsmeqihycubc9hn X-Rspamd-Queue-Id: 22A9A4000A X-Rspamd-Server: rspam11 X-HE-Tag: 1722881582-210075 X-HE-Meta: U2FsdGVkX1+XgfVOjCC4y2mJCYzJI/ybdprn04a41RldPdJR6ofRyOGInCfeL5DatToPu5aKkYpu1Vfl3IzrIRBaXEuQUfxhw8RdZmE+rlitHEp0VgxYHjb0BdulJW2bJeWRi/l2RDJGk6P+pjFtsA4Pkui6P+UkXBiQw2KKTh5ZAvNNT36swJ7mzI1toN8XBd93TNkJyA65ibsbRmmlR889M6qmB6J36LSIgEpGqLFJtNffu8rjIH7CPlc36B2dTjpsFuptHHweS2NMFq+KSnYd7UaE0PAQf7Gxx80J1y6NVGHKuqnHNP5snJ1AUv9AufxK9uFxExbYSgp31A3E8W3R5MRqxDC/fE9GWpUxv8SE+Qq6zWWq6//wFBF1YmnFDZrmv84SQmrvFw3LAgSnNPeT7sXZloervcn57YfIwOLNjfmyiJoV3hMQkIWgJ+vf8J5LHPSrFWf0YgZyYykhE19Cnh6Ng14Agmo1M4/ZPWE2JFFw+Tgf2+SCsAMHKTB5ah42bu8hlOx3y+zSurZpLi4vD5TTIC0XUfskj7egfutnXEx6j6BpsmpEwUBNDOo8Ocpvl/eYv9yPTRUJP95VVpV508/V+M3LnfCijZjKPDrW/WDBCT/BS6PCqZpyV9SJH3AONejjb251P2SF8Ye8OgZeX3LNR5YF7k0Uuk+7RqARi5xhumeU8P0n3fooqphoVBUboHUyvhfAwpZPYwKjZ+M+W4LREsHcEJegaCyJTDphYx0eNCRHOJbdo0BzR+828KF6JPpSrb1JoRxLQSOIbEsTBOe6NEu/TxOgYDDQyvMUWLyUS1izy+06pyNaM4fIneHwwi7Ppy106zUqJRZu1SIwyZ4gd5dZ+qL77KXE/LJUZbVGC8wicyKA4mCf+B2PMXXwTAOqEGeXt6O59t5AyZicOnZlkPcyfORD/uW3KogY1GzhLMk35yGeQkAHMUyujKMP9y8mx/C8ICRkZKj NYO91JIH Uux0El9B+JxAMIewHD5Wu0X997/AuLsFOZ571X+i6WSv2ZCEEZeOtLZy/VZVYrN6HrYfjWBLWQzCl/8F/tm+M5mrIzet44rUgTHXEMjA/4Euz+fYl0G+GLXrbI67exPqLQRCp0MvK/crW787UBYGobqYlNE6ETGrt0nl1ZOpuvU9Eb+0P55cBirgfHV5lF1rYHxlN2gvgwhiTv6jtzInvv20fXwfhJB9jipmnvxV7FZHjJmGFKAyofxNQBeS3xf2Q4MypDchyk/g4C1DRcZYnD/PnmUaUFRHqhc8mx2f3yn4DMb9ZW7grVr2DZga7ODk/EOmiSh9Y85eTxYympopwLt+Itg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.003737, 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 Mon, 5 Aug 2024 at 18:19, Ackerley Tng wrote: > > Fuad Tabba writes: > > > Add the KVM capability KVM_CAP_GUEST_MEMFD_MAPPABLE, which is > > true if mapping guest memory is supported by the host. > > > > Signed-off-by: Fuad Tabba > > --- > > include/uapi/linux/kvm.h | 3 ++- > > virt/kvm/kvm_main.c | 4 ++++ > > 2 files changed, 6 insertions(+), 1 deletion(-) > > > > > > Why do we need a cap for `KVM_CAP_GUEST_MEMFD_MAPPABLE` instead of just > making guest_memfd mmap-able? > > Is this to prevent breaking userspace, because a user might be relying > on guest_memfd being not mmap-able? To be able to check that the ability is there, since it is a new capability not available in Linux 6.9 not 6.10 (i.e., after guest_memfd()) was introduced. Cheers, /fuad