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AJvYcCUZbV0gNhre3jO9UOcNZltDi38TU6yas0E/P9vQ8Bxo4GpsfgPwCOtjhBOZrwCA2yceYDmulQH17w==@kvack.org X-Gm-Message-State: AOJu0YxW0P2MwIL4DwzZVZjCfU92nfbz/YMvBd0H9PJVhHkyt3JHQ5q4 88Nd8G1K9Hg3HmNyxkr4BuewTRq5TVA/OWXP7Pojo086po7s83fqhJhUrm5e+3zU+VloLgYhYA0 ff4I7mA== X-Google-Smtp-Source: AGHT+IHLtmM9b2ohCo6v8xL5lzq5k6sLkOhmrbwVm3iSaR1J0L8EXLNkJNiYHZYz68JZXhiAQifqzelMv8o= X-Received: from pjk13.prod.google.com ([2002:a17:90b:558d:b0:312:ea08:fa64]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90a:d00c:b0:311:c1ec:7d05 with SMTP id 98e67ed59e1d1-31caf92238dmr25136631a91.35.1753116274516; Mon, 21 Jul 2025 09:44:34 -0700 (PDT) Date: Mon, 21 Jul 2025 09:44:33 -0700 In-Reply-To: <20250717162731.446579-4-tabba@google.com> Mime-Version: 1.0 References: <20250717162731.446579-1-tabba@google.com> <20250717162731.446579-4-tabba@google.com> Message-ID: Subject: Re: [PATCH v15 03/21] KVM: Introduce kvm_arch_supports_gmem() From: Sean Christopherson To: Fuad Tabba Cc: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, kvmarm@lists.linux.dev, pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, 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, ackerleytng@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, ira.weiny@intel.com Content-Type: text/plain; charset="us-ascii" X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: B121E180005 X-Stat-Signature: m9c35u7sy1hhgyeuwspztymdg45aycdh X-Rspam-User: X-HE-Tag: 1753116275-360363 X-HE-Meta: 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 492GP+Nm 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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: On Thu, Jul 17, 2025, Fuad Tabba wrote: > Introduce kvm_arch_supports_gmem() to explicitly indicate whether an > architecture supports guest_memfd. > > Previously, kvm_arch_has_private_mem() was used to check for guest_memfd > support. However, this conflated guest_memfd with "private" memory, > implying that guest_memfd was exclusively for CoCo VMs or other private > memory use cases. > > With the expansion of guest_memfd to support non-private memory, such as > shared host mappings, it is necessary to decouple these concepts. The > new kvm_arch_supports_gmem() function provides a clear way to check for > guest_memfd support. > > Reviewed-by: Ira Weiny > Reviewed-by: Gavin Shan > Reviewed-by: Shivank Garg > Reviewed-by: Vlastimil Babka > Reviewed-by: Xiaoyao Li > Co-developed-by: David Hildenbrand > Signed-off-by: David Hildenbrand > Signed-off-by: Fuad Tabba > --- > arch/x86/include/asm/kvm_host.h | 4 +++- > include/linux/kvm_host.h | 11 +++++++++++ > virt/kvm/kvm_main.c | 4 ++-- > 3 files changed, 16 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index acb25f935d84..bde811b2d303 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -2277,8 +2277,10 @@ void kvm_configure_mmu(bool enable_tdp, int tdp_forced_root_level, > > #ifdef CONFIG_KVM_GMEM > #define kvm_arch_has_private_mem(kvm) ((kvm)->arch.has_private_mem) > +#define kvm_arch_supports_gmem(kvm) kvm_arch_has_private_mem(kvm) Don't support/use macros, just make kvm_arch_supports_gmem() a "normal" arch hook. kvm_arch_has_private_mem() is a macro so that kvm_arch_nr_memslot_as_ids() can resolve to a compile-time constant when CONFIG_KVM_GMEM is false, and so that it's a trivial check when true. kvm_arch_supports_gmem() is only ever used in slow paths, check_memory_region_flags() and kvm_vm_ioctl_check_extension_generic(). Of course, after my suggestions from patch 2, it goes away completely. > #else > #define kvm_arch_has_private_mem(kvm) false > +#define kvm_arch_supports_gmem(kvm) false This is silly. It adds code to x86 *and* makes the generic code more complex. Again, a moot point in the end, but for future reference this isn't a pattern we should encourage.