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AJvYcCWsBkkRd+G9fk5tdzLzKJXiKDky+gqsNhSwo4ranrup8Whv6D16672tkP2EjIfIE57bqM9Iwoqi3Q==@kvack.org X-Gm-Message-State: AOJu0Yyj9hM/WMkX1oxTh22B4p0O1ZGVpu1Kme+CRn1JifMFsNqoprEL t9JtVTTIWcCQkFe2bEi4cGT5fqF8fYM86gvxuhOQkwLzdIf4bQLmgZMPpDw8EqJYkTdkBuWBiJV aMQaz1A== X-Google-Smtp-Source: AGHT+IHpWV5RNhKUXvWMGZ+xD8d/MTd1Ze+E21K0nbVEiBP6P7EQ34tE5jerqVVq8m5WkJ7UUYnKv9jKozQ= X-Received: from pjbsd7.prod.google.com ([2002:a17:90b:5147:b0:33b:b3b8:216b]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:3141:b0:32d:e07f:3236 with SMTP id 98e67ed59e1d1-33bcf8e3ab0mr32372876a91.22.1761231935591; Thu, 23 Oct 2025 08:05:35 -0700 (PDT) Date: Thu, 23 Oct 2025 08:05:33 -0700 In-Reply-To: Mime-Version: 1.0 References: <8ee16fbf254115b0fd72cc2b5c06d2ccef66eca9.1760731772.git.ackerleytng@google.com> <2457cb3b-5dde-4ca1-b75d-174b5daee28a@arm.com> Message-ID: Subject: Re: [RFC PATCH v1 07/37] KVM: Introduce KVM_SET_MEMORY_ATTRIBUTES2 From: Sean Christopherson To: Ackerley Tng Cc: Steven Price , cgroups@vger.kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org, akpm@linux-foundation.org, binbin.wu@linux.intel.com, bp@alien8.de, brauner@kernel.org, chao.p.peng@intel.com, chenhuacai@kernel.org, corbet@lwn.net, dave.hansen@intel.com, dave.hansen@linux.intel.com, david@redhat.com, dmatlack@google.com, erdemaktas@google.com, fan.du@intel.com, fvdl@google.com, haibo1.xu@intel.com, hannes@cmpxchg.org, hch@infradead.org, hpa@zytor.com, hughd@google.com, ira.weiny@intel.com, isaku.yamahata@intel.com, jack@suse.cz, james.morse@arm.com, jarkko@kernel.org, jgg@ziepe.ca, jgowans@amazon.com, jhubbard@nvidia.com, jthoughton@google.com, jun.miao@intel.com, kai.huang@intel.com, keirf@google.com, kent.overstreet@linux.dev, liam.merwick@oracle.com, maciej.wieczor-retman@intel.com, mail@maciej.szmigiero.name, maobibo@loongson.cn, mathieu.desnoyers@efficios.com, maz@kernel.org, mhiramat@kernel.org, mhocko@kernel.org, mic@digikod.net, michael.roth@amd.com, mingo@redhat.com, mlevitsk@redhat.com, mpe@ellerman.id.au, muchun.song@linux.dev, nikunj@amd.com, nsaenz@amazon.es, oliver.upton@linux.dev, palmer@dabbelt.com, pankaj.gupta@amd.com, paul.walmsley@sifive.com, pbonzini@redhat.com, peterx@redhat.com, pgonda@google.com, prsampat@amd.com, pvorel@suse.cz, qperret@google.com, richard.weiyang@gmail.com, rick.p.edgecombe@intel.com, rientjes@google.com, rostedt@goodmis.org, roypat@amazon.co.uk, rppt@kernel.org, shakeel.butt@linux.dev, shuah@kernel.org, suzuki.poulose@arm.com, tabba@google.com, tglx@linutronix.de, thomas.lendacky@amd.com, vannapurve@google.com, vbabka@suse.cz, viro@zeniv.linux.org.uk, vkuznets@redhat.com, will@kernel.org, willy@infradead.org, wyihan@google.com, xiaoyao.li@intel.com, yan.y.zhao@intel.com, yilun.xu@intel.com, yuzenghui@huawei.com Content-Type: text/plain; charset="us-ascii" X-Rspamd-Server: rspam05 X-Stat-Signature: hukirss17hbqw3du6whunts9angysj3q X-Rspam-User: X-Rspamd-Queue-Id: 376F21C000A X-HE-Tag: 1761231937-807148 X-HE-Meta: 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 uqnK4XYi 9mISPYXXA0EGHpVs4lM/ZI0Ur4acP6oro8+dzuQjomufLNu/A6beo+jevNW3X2ISNDwZSzQcEwUy77PdyuQcQAGmuqPqfd2EGCnOErhzpXqs254UPXaRZCpvmdD30FUTDlC2YXZ3baZORMDJIFN6lLoUY9ytiADM3Bj0pH/0r7kjn+sNZEPxSZ4cESqTQtYc8hQH/j/l8WabTztgi7RFQth+5K3O4l/9x2oddRsqPS1FV5WLKvwL+50WzrxIOmdS0BejI3HaUKi50fr06DkHY9gmxr65XJJWAnupgunEiyNCcFdo7n5EFMkYzL/Mii2YnckVasPyW6GzaEBUgKDs4rFQd8OAMUB6DIVd8dsazPL6omyGVBdeHSWeRT9cjZEYY2rbgDO2rLGcvyVtRrRmrWKJ04tMZHgf/W5sjRC5XhMI3hfJXU3cF3vpYlbPY/MfmrqorEVutZfMxLRodgKAcv/sDDY07jTwvYQ9VVpXcF73UiN4wASLKwV7/97whjgZGzcG7Ydkb0crq9ZCy31aDJFy6NfVqD2Mp5o6Sn1hM2L5EqojRi3ZDZdgj4UT44mw7ta5SLaTEnAXMbYiVWZYf2QvoaM8NpqQu3IF4wQyiZYITb42MhvhQb8qVBsbo6bVB1hSAdovhKCjbf4VSii3fb+MUZQ== 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: On Thu, Oct 23, 2025, Ackerley Tng wrote: > Sean Christopherson writes: > > > On Wed, Oct 22, 2025, Ackerley Tng wrote: > >> Ackerley Tng writes: > >> > >> Found another issue with KVM_CAP_MEMORY_ATTRIBUTES2. > >> > >> KVM_CAP_MEMORY_ATTRIBUTES2 was defined to do the same thing as > >> KVM_CAP_MEMORY_ATTRIBUTES, but that's wrong since > >> KVM_CAP_MEMORY_ATTRIBUTES2 should indicate the presence of > >> KVM_SET_MEMORY_ATTRIBUTES2 and struct kvm_memory_attributes2. > > > > No? If no attributes are supported, whether or not KVM_SET_MEMORY_ATTRIBUTES2 > > exists is largely irrelevant. > > That's true. > > > We can even provide the same -ENOTTY errno by > > checking that _any_ attributes are supported, i.e. so that doing > > KVM_SET_MEMORY_ATTRIBUTES2 on KVM without any support whatsoever fails in the > > same way that KVM with code support but no attributes fails. > > IIUC KVM_SET_MEMORY_ATTRIBUTES doesn't fail with -ENOTTY now when there > are no valid attributes. > > Even if there's no valid attributes (as in > kvm_supported_mem_attributes() returns 0), it's possible to call > KVM_SET_MEMORY_ATTRIBUTES with .attributes set to 0, which will be a > no-op, but will return 0. > > I think this is kind of correct behavior since .attributes = 0 is > actually a valid expression for "I want this range to be shared", and > for a VM that doesn't support private memory, it's a valid expression. > > > The other way that there are "no attributes" would be if there are no > /VM/ attributes, in which case KVM_SET_MEMORY_ATTRIBUTES, sent to as a > vm ioctl, will return -ENOTTY. Ya, this is what I was trying to say with "_any_ attributes are supported". I.e. by "any" I meant "any attributes in KVM for VMs vs. gmems", not "any attributes for this specific VM/gmem instance". > > In other words, I don't see why it can't do both. Even if we can't massage the > > right errno, I would much rather KVM_SET_MEMORY_ATTRIBUTES2 enumerate the set of > > Did you mean KVM_CAP_MEMORY_ATTRIBUTES2 in the line above? Doh, yes.