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[2003:cb:c70b:db00:724d:8b0c:110e:3713]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-438b1718741sm24332155e9.0.2025.01.22.14.07.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 22 Jan 2025 14:07:03 -0800 (PST) Message-ID: <647bbdac-df82-4cdb-a3e9-287d439b4ef7@redhat.com> Date: Wed, 22 Jan 2025 23:06:59 +0100 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 1/9] KVM: guest_memfd: Allow host to mmap 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: <20250122152738.1173160-1-tabba@google.com> <20250122152738.1173160-2-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 22.01.25 16:27, Fuad Tabba wrote: > Add support for mmap() and fault() for guest_memfd 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 architecture has that support, and only allows mmap() > if that's the case. > > Additionally, this is gated with a new configuration option, > CONFIG_KVM_GMEM_MAPPABLE. > > Signed-off-by: Fuad Tabba > --- > arch/x86/include/asm/kvm_host.h | 2 + > include/linux/kvm_host.h | 11 +++++ > virt/kvm/Kconfig | 4 ++ > virt/kvm/guest_memfd.c | 71 +++++++++++++++++++++++++++++++++ > 4 files changed, 88 insertions(+) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index e159e44a6a1b..c0e149bc1d79 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -2206,6 +2206,8 @@ void kvm_configure_mmu(bool enable_tdp, int tdp_forced_root_level, > #define kvm_arch_has_private_mem(kvm) false > #endif > > +#define kvm_arch_private_mem_inplace(kvm) false > + > #define kvm_arch_has_readonly_mem(kvm) (!(kvm)->arch.has_protected_state) > > static inline u16 kvm_read_ldt(void) > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 401439bb21e3..ebca0ab4c5e2 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_private_mem_inplace if support for private > + * memory is enabled it supports in-place conversion between shared and private. > + */ > +#if !defined(kvm_arch_private_mem_inplace) && !IS_ENABLED(CONFIG_KVM_PRIVATE_MEM) > +static inline bool kvm_arch_private_mem_inplace(struct kvm *kvm) I assume right now this would rather indicate "support for shared (mappable) memory in guest_memfd". Maybe there is a better way to express that :) kvm_arch_gmem_supports_shared_mem ? The in-place conversion is (at least to me) implied with support for shared memory. > + > #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..59400fd8f539 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_MAPPABLE > + select KVM_PRIVATE_MEM Easier to grasp might be: KVM_GMEM_MAPPABLE -> KVM_GMEM_SHARED_MEM Support for "shared" memory kind of imply mmap support (otherwise, how to make use of it :) ), (KVM_PRIVATE_MEM -> KVM_GMEM might also make sense, but it's a different discussion) > + bool > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 47a9f68f7b24..9ee162bf6bde 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -307,7 +307,78 @@ 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_MAPPABLE > +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); Would the idea be later that kvm_gmem_get_folio() would fail on private memory, or do you envision other checks in this code here in the future? -- Cheers, David / dhildenb