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Mon, 10 Feb 2025 00:33:43 -0800 (PST) MIME-Version: 1.0 References: <20250129172320.950523-1-tabba@google.com> <20250129172320.950523-4-tabba@google.com> <0b1cc981-52e8-4f8f-846a-f19507e3a630@amazon.co.uk> In-Reply-To: <0b1cc981-52e8-4f8f-846a-f19507e3a630@amazon.co.uk> From: Fuad Tabba Date: Mon, 10 Feb 2025 08:33:05 +0000 X-Gm-Features: AWEUYZnqRWolgaEQBxdtLu3-bmijaxjyQYTiw-VQAkPGP95c4FrJsH5ujWBm14U Message-ID: Subject: Re: [RFC PATCH v2 03/11] KVM: guest_memfd: Allow host to map guest_memfd() pages To: Patrick Roy Cc: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, 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, 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, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Queue-Id: 1AE94C0006 X-Rspamd-Server: rspam12 X-Stat-Signature: ofcx8uf17nyoi9pm4df7etewgie1ib8k X-HE-Tag: 1739176425-657106 X-HE-Meta: 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 7rrtIXd7 jGyH8Rjckr3BbwBMlAh0Xfaul2ciFabvEmpnVKtM4VCG5H+cBMinOqHYGTLjaB/SrgkikLCNj7GxbYAMybi3tvgYKiVNhnQlj1GdEW+h89YSuWx+3cRNEe2BwwVWsPp9MFJMKCZ9SBzIwrnmHqXxmhozwKkvPmD4XpTcMIaGdUlyXCDPnt/fRKlFWi0WRuWe5dJwaBvmZqKLjhXdBG/62jC5ZtTABnI8NIKne5D72CAGYu31b+kAr1jaZEyM3lhCx99Hp2jEk66qZeC3LZD5RmtEG2V7WO4WoITT9AEDn9iXq9WmNmBqc/SxGeTcvVXU2sMb/inv1nvSnnjqE+dn7ffdnsEPJm3uozOt1xsZoPhyf2nEKeD5Fo8F7ha0oNMTHVCSCLn/ZKKgpG+B0OlNgly/FfQ== 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 Fri, 7 Feb 2025 at 16:45, Patrick Roy wrote: > > Hi Fuad! > > On Wed, 2025-01-29 at 17:23 +0000, 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(+) > > > > -snip- > > > > 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; > > + } > > + > > + 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; > > + } > > + > > + if (!folio_test_uptodate(folio)) { > > + clear_highpage(folio_page(folio, 0)); > > + folio_mark_uptodate(folio); > > kvm_gmem_mark_prepared() instead of direct folio_mark_uptodate() here, I > think (in preparation of things like [1])? Noticed this while rebasing > my direct map removal series on top of this and wondering why mmap'd > folios sometimes didn't get removed (since it hooks mark_prepared()). Thanks for pointing that out. Will fix. /fuad > Best, > Patrick > > [1]: https://lore.kernel.org/kvm/20241108155056.332412-1-pbonzini@redhat.com/