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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> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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" 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.