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[2003:cb:c713:3b00:16ce:8f1c:dd50:90fb]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-438e244eb0dsm30102555e9.27.2025.01.30.09.20.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Jan 2025 09:20:28 -0800 (PST) Message-ID: <07e7e09a-997e-444e-92bf-8f2359a36cbd@redhat.com> Date: Thu, 30 Jan 2025 18:20:26 +0100 Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2 03/11] KVM: guest_memfd: Allow host to map guest_memfd() pages To: Fuad Tabba , kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org Cc: 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, ackerleytng@google.com, mail@maciej.szmigiero.name, 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 References: <20250129172320.950523-1-tabba@google.com> <20250129172320.950523-4-tabba@google.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 29.01.25 18:23, Fuad Tabba wrote: > Add support for mmap() and fault() for guest_memfd backed memory > in the host for VMs that support in-place conversion between > shared and private (shared memory). To that end, this patch adds > the ability to check whether the VM type has that support, and > only allows mapping its memory if that's the case. > > Additionally, this behavior is gated with a new configuration > option, CONFIG_KVM_GMEM_SHARED_MEM. > > Signed-off-by: Fuad Tabba > > --- > > This patch series will allow shared memory support for software > VMs in x86. It will also introduce a similar VM type for arm64 > and allow shared memory support for that. In the future, pKVM > will also support shared memory. > --- > include/linux/kvm_host.h | 11 ++++++ > virt/kvm/Kconfig | 4 +++ > virt/kvm/guest_memfd.c | 77 ++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 92 insertions(+) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 401439bb21e3..408429f13bf4 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -717,6 +717,17 @@ static inline bool kvm_arch_has_private_mem(struct kvm *kvm) > } > #endif > > +/* > + * Arch code must define kvm_arch_gmem_supports_shared_mem if support for > + * private memory is enabled and it supports in-place shared/private conversion. > + */ > +#if !defined(kvm_arch_gmem_supports_shared_mem) && !IS_ENABLED(CONFIG_KVM_PRIVATE_MEM) > +static inline bool kvm_arch_gmem_supports_shared_mem(struct kvm *kvm) > +{ > + return false; > +} > +#endif > + > #ifndef kvm_arch_has_readonly_mem > static inline bool kvm_arch_has_readonly_mem(struct kvm *kvm) > { > diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig > index 54e959e7d68f..4e759e8020c5 100644 > --- a/virt/kvm/Kconfig > +++ b/virt/kvm/Kconfig > @@ -124,3 +124,7 @@ config HAVE_KVM_ARCH_GMEM_PREPARE > config HAVE_KVM_ARCH_GMEM_INVALIDATE > bool > depends on KVM_PRIVATE_MEM > + > +config KVM_GMEM_SHARED_MEM > + select KVM_PRIVATE_MEM > + bool > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 47a9f68f7b24..86441581c9ae 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -307,7 +307,84 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn) > return gfn - slot->base_gfn + slot->gmem.pgoff; > } > > +#ifdef CONFIG_KVM_GMEM_SHARED_MEM > +static vm_fault_t kvm_gmem_fault(struct vm_fault *vmf) > +{ > + struct inode *inode = file_inode(vmf->vma->vm_file); > + struct folio *folio; > + vm_fault_t ret = VM_FAULT_LOCKED; > + > + filemap_invalidate_lock_shared(inode->i_mapping); > + > + folio = kvm_gmem_get_folio(inode, vmf->pgoff); > + if (IS_ERR(folio)) { > + ret = VM_FAULT_SIGBUS; > + goto out_filemap; > + } > + > + if (folio_test_hwpoison(folio)) { > + ret = VM_FAULT_HWPOISON; > + goto out_folio; > + } > + Worth adding a comment, something like /* * Only private folios are marked as "guestmem" so far, and we never * expect private folios at this point. */ > + if (WARN_ON_ONCE(folio_test_guestmem(folio))) { > + ret = VM_FAULT_SIGBUS; > + goto out_folio; > + } > + > + /* No support for huge pages. */ > + if (WARN_ON_ONCE(folio_nr_pages(folio) > 1)) { > + ret = VM_FAULT_SIGBUS; > + goto out_folio; > + } > + /* We only support mmap of small folios. */ VM_WARN_ON_ONCE(folio_test_large(folio)); > + if (!folio_test_uptodate(folio)) { > + clear_highpage(folio_page(folio, 0)); > + folio_mark_uptodate(folio); > + } > + > + vmf->page = folio_file_page(folio, vmf->pgoff); > + Apart from that LGTM. -- Cheers, David / dhildenb