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AJvYcCVrZoRHd3EuaLzdg7sbB5kE5UKdY8geyyTWf+Wop8YbloX0CsfTyg8r60hmzuRE94fE5MkJjgBgfg==@kvack.org X-Gm-Message-State: AOJu0YwNEh3e4Qw4Rj11RLzpFB+vDPuCjd1yUZ27uTTGqb+bzGNR5Wwe QwxNwknF1709bcbjzLtEZiJB5doOQSFQBoJe4jcNtxzHZg+eZlFNNUNheasYQJNDXLKN3EHzY+p pf1t6Ugk3yBLZ09au7JkyDg== X-Google-Smtp-Source: AGHT+IF4sKMX+KgxjFI4PsB328sWkz/ZZMywxzy98yOo2qwvaqGJzCDlFLnSzmt/3FCDRYVqBqf7nAmLzbgghsG8Ug== X-Received: from pji8.prod.google.com ([2002:a17:90b:3fc8:b0:2fa:1fac:269c]) (user=ackerleytng job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90a:e185:b0:2ee:8430:b831 with SMTP id 98e67ed59e1d1-2fbf5bc0249mr1883029a91.2.1739319348587; Tue, 11 Feb 2025 16:15:48 -0800 (PST) Date: Wed, 12 Feb 2025 00:15:47 +0000 In-Reply-To: <20250211121128.703390-6-tabba@google.com> (message from Fuad Tabba on Tue, 11 Feb 2025 12:11:21 +0000) Mime-Version: 1.0 Message-ID: Subject: Re: [PATCH v3 05/11] KVM: guest_memfd: Handle in-place shared memory as guest_memfd backed memory 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, 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, jthoughton@google.com, tabba@google.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: E1DD740004 X-Stat-Signature: hi8mbnxnidas19wytzj4xb63a1j84aup X-Rspam-User: X-HE-Tag: 1739319349-184048 X-HE-Meta: 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 c76pLox0 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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: > For VMs that allow sharing guest_memfd backed memory in-place, > handle that memory the same as "private" guest_memfd memory. This > means that faulting that memory in the host or in the guest will > go through the guest_memfd subsystem. > > Note that the word "private" in the name of the function > kvm_mem_is_private() doesn't necessarily indicate that the memory > isn't shared, but is due to the history and evolution of > guest_memfd and the various names it has received. In effect, > this function is used to multiplex between the path of a normal > page fault and the path of a guest_memfd backed page fault. > Thanks for this summary! It has always been confusing and this really helps. Is there any chance we could rename the functions in KVM, or maybe add a comment at the function definitions? The name of the userspace flag will have to remain, of course. > Signed-off-by: Fuad Tabba > --- > include/linux/kvm_host.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 438aa3df3175..39fd6e35c723 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -2521,7 +2521,8 @@ static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn) > #else > static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn) > { > - return false; > + return kvm_arch_gmem_supports_shared_mem(kvm) && > + kvm_slot_can_be_private(gfn_to_memslot(kvm, gfn)); > } > #endif /* CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES */