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[2003:cb:c706:2000:e44c:bc46:d8d3:be5]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43986320899sm109955095e9.38.2025.02.20.03.58.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Feb 2025 03:58:24 -0800 (PST) Message-ID: <2cdc5414-a280-4c47-86d5-4261a12deab6@redhat.com> Date: Thu, 20 Feb 2025 12:58:20 +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: [PATCH v4 03/10] 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, 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: <20250218172500.807733-1-tabba@google.com> <20250218172500.807733-4-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 18.02.25 18:24, 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. To that end, this patch adds the ability to > check whether the VM type supports in-place conversion, and only > allows mapping its memory if that's the case. > > This behavior is also gated by the configuration option > KVM_GMEM_SHARED_MEM. > > Signed-off-by: Fuad Tabba > --- > include/linux/kvm_host.h | 11 +++++ > virt/kvm/guest_memfd.c | 103 +++++++++++++++++++++++++++++++++++++++ > 2 files changed, 114 insertions(+) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 3ad0719bfc4f..f9e8b10a4b09 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -728,6 +728,17 @@ 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/guest_memfd.c b/virt/kvm/guest_memfd.c > index c6f6792bec2a..30b47ff0e6d2 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -317,9 +317,112 @@ void kvm_gmem_handle_folio_put(struct folio *folio) > { > WARN_ONCE(1, "A placeholder that shouldn't trigger. Work in progress."); > } > + > +static bool kvm_gmem_offset_is_shared(struct file *file, pgoff_t index) > +{ > + struct kvm_gmem *gmem = file->private_data; > + > + /* For now, VMs that support shared memory share all their memory. */ > + return kvm_arch_gmem_supports_shared_mem(gmem->kvm); > +} > + > +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)) { > + switch (PTR_ERR(folio)) { > + case -EAGAIN: > + ret = VM_FAULT_RETRY; > + break; > + case -ENOMEM: > + ret = VM_FAULT_OOM; > + break; > + default: > + ret = VM_FAULT_SIGBUS; > + break; > + } > + goto out_filemap; > + } > + > + if (folio_test_hwpoison(folio)) { > + ret = VM_FAULT_HWPOISON; > + goto out_folio; > + } > + > + /* Must be called with folio lock held, i.e., after kvm_gmem_get_folio() */ > + if (!kvm_gmem_offset_is_shared(vmf->vma->vm_file, vmf->pgoff)) { > + ret = VM_FAULT_SIGBUS; > + goto out_folio; > + } > + > + /* > + * 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_test_large(folio))) { > + ret = VM_FAULT_SIGBUS; > + goto out_folio; > + } > + > + if (!folio_test_uptodate(folio)) { > + clear_highpage(folio_page(folio, 0)); > + kvm_gmem_mark_prepared(folio); > + } kvm_gmem_get_pfn()->__kvm_gmem_get_pfn() seems to call kvm_gmem_prepare_folio() instead. Could we do the same here? -- Cheers, David / dhildenb