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AJvYcCXdXt3bwiNmTh6vJRKVmhk3q37UXpBrLbxF0YAvfk86uzubEznLbZLjhjJrhBK+FNVycmB5DRQn1A==@kvack.org X-Gm-Message-State: AOJu0Yz7vqEMLSZww2Bd/PVnwd1qvF3bviCewA+n2OmR06duqVW9Zt8S m3TgMHY6EV6utDYNNeSzy4jT8b9kOPU64DPILJ18o3ntT6eODjFG7BOMQMfuP0qG5arNSftEASK mDum4m+VRUEYInCjW5Jc/XofaU9eFb/Ui1HnY X-Gm-Gg: ASbGnctIBD2YR5QPxG8XVFAAj5N2RtqROVpfQgVCoBvozIVbINabL6TCjcP9EtwMO6V P6vK2FgFXhIEueMlwIbukMFJ2MrlUPXJPzReBiaFJTFV8hW94vh5BF5OmgRTqp7/Wvwws3eN4cK aMbK/zK7W82k471sP+C43cq6P0mxFbrIxX3w/JYOj3fUx19vwEtfRT0xVNkFRbAnEK2lLw6KSnG A== X-Google-Smtp-Source: AGHT+IEYxfy+iIaUBNgU9T6jCSjA/oXKOMtzoXjq1V2q9P4pPr/RlKitvANriEH2zjTwxWX+k/0FVFwiTWXwlL2OCdE= X-Received: by 2002:a05:690c:2020:b0:70a:4540:c8dd with SMTP id 00721157ae682-70a4540cc82mr141639737b3.32.1747078208889; Mon, 12 May 2025 12:30:08 -0700 (PDT) MIME-Version: 1.0 References: <20250430165655.605595-1-tabba@google.com> <20250430165655.605595-9-tabba@google.com> <702d9951-ac26-4ee4-8a78-d5104141c2e4@redhat.com> In-Reply-To: From: James Houghton Date: Mon, 12 May 2025 12:29:33 -0700 X-Gm-Features: AX0GCFtYFUIZ8MQMW02UoIlsS1ifURM47rF6GhrxE2cY-QHs4awlqCbXiPDlOAk Message-ID: Subject: Re: [PATCH v8 08/13] KVM: guest_memfd: Allow host to map guest_memfd() pages To: Fuad Tabba Cc: David Hildenbrand , 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, 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, peterx@redhat.com, pankaj.gupta@amd.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: ez4m7dkh4wph1zfr7c5fr1ao43ehck9b X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 1A4EC20014 X-HE-Tag: 1747078210-857804 X-HE-Meta: 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 AiaOMfvf OPxtDK0T8RyXBWo8v1kDLddVUGufP/o+nIQ0T/fjBzBwDXqBUQpVLezQwnE9UPuUUYk5hEOPS5+6kGOQMtzwSwoJTvApTCVcxzBlJtZvgardW7PWNky6HxJpkAuKcOkuXZaRXdZlIeK7YBIi/b3dTWDyyS7J5LPWlyfN8h0PvN0o2we94YGiDbJH9rdexJ+5m7S83i3+X4M1qjmqDfLvWLhkkXg33EA5EULdGgaESHJ3YMO/rjxFC3eGaDIG3BrwX2eW7/saFbPsgWCrGPjCpxqhBP0TAkMlTqxXL/tKLsRJJrpaewW6qQfKMucn3nv68pBD864SuRVGuO+6QFZDnXmMnFdQlqaj2BjIj3XQ4eYQKwyr6yoRqTpDHJ0+X7zP+qv3lfvs0Dv15k6N8IzmR06c2xw== 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 Mon, May 12, 2025 at 12:09=E2=80=AFAM Fuad Tabba wrot= e: > > Hi James. > > On Sun, 11 May 2025 at 09:03, David Hildenbrand wrote: > > > > On 09.05.25 22:54, James Houghton wrote: > > > On Wed, Apr 30, 2025 at 9:57=E2=80=AFAM Fuad Tabba = wrote: > > >> +static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *= vma) > > >> +{ > > >> + struct kvm_gmem *gmem =3D file->private_data; > > >> + > > >> + if (!kvm_arch_gmem_supports_shared_mem(gmem->kvm)) > > >> + return -ENODEV; > > >> + > > >> + if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) !=3D > > >> + (VM_SHARED | VM_MAYSHARE)) { > > >> + return -EINVAL; > > >> + } > > >> + > > >> + vm_flags_set(vma, VM_DONTDUMP); > > > > > > Hi Fuad, > > > > > > Sorry if I missed this, but why exactly do we set VM_DONTDUMP here? > > > Could you leave a small comment? (I see that it seems to have > > > originally come from Patrick? [1]) I get that guest memory VMAs > > > generally should have VM_DONTDUMP; is there a bigger reason? > > > > (David replying) > > > > I assume because we might have inaccessible parts in there that SIGBUS > > on access. > > That was my thinking. > > > get_dump_page() does ignore any errors, though (returning NULL), so > > likely we don't need VM_DONTDUMP. > > In which case I'll remove this from the next respin. SGTM, thanks! Userspace could remove VM_DONTDUMP by doing MADV_DODUMP, which is why I was curious about this. And thanks for the extra context[1], Patrick. :) [1]: https://lore.kernel.org/kvm/20250512074615.27394-1-roypat@amazon.co.uk= /