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Thu, 20 Feb 2025 03:38:48 -0800 (PST) MIME-Version: 1.0 References: <20250211121128.703390-1-tabba@google.com> <20250211121128.703390-3-tabba@google.com> <8ddab670-8416-47f2-a5a6-94fb3444f328@redhat.com> In-Reply-To: <8ddab670-8416-47f2-a5a6-94fb3444f328@redhat.com> From: Fuad Tabba Date: Thu, 20 Feb 2025 11:38:11 +0000 X-Gm-Features: AWEUYZlLBl7dDLqJoCpruqAIeCElYd6ktqwd6C4yBJhwMu65f7HQaGbNsfNEeIU Message-ID: Subject: Re: [PATCH v3 02/11] KVM: guest_memfd: Handle final folio_put() of guest_memfd pages To: David Hildenbrand 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, 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 Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Queue-Id: 8260F40014 X-Stat-Signature: roe8gwscn46xqfjfc1cr5o73kiobwq3u X-Rspamd-Server: rspam03 X-HE-Tag: 1740051529-78631 X-HE-Meta: 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 KflP8q7Y Na9ukrYNPAcaQ/qqIICR8qkestS8PeXjMQKD/gpHD10mWA6CYa+5soXWmcWnLdZcm5rDwlBfGbFAI46dgqkpxAv65ynwnBH8tohrTFE/NXKcqqn6IADfv/gO9voqJIZJcopwAX8z1T6PzDEEkIuVi35ukJpjTUH9VBv3El+l2OGGZRZh+F7e9J/fNPVIvBwNVCG90qoLn7ddCO89x9jeE+57MikPMFESZdLhmho85EDnq4gH/h1aD8zKnuFQ2p5bvRBWcx2m7UMEyWGKk8sg+4QQxlHgHo905Z3R0f+QDYIBKDZg8h61ggpNf35cuTvNeStIx6s3ajL8ZeSqESaf9znZgHj99nHRQOF6qDsWwxgLWDH0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000110, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi David, On Thu, 20 Feb 2025 at 11:25, David Hildenbrand wrote: > > On 11.02.25 13:11, Fuad Tabba wrote: > > Before transitioning a guest_memfd folio to unshared, thereby > > disallowing access by the host and allowing the hypervisor to > > transition its view of the guest page as private, we need to be > > sure that the host doesn't have any references to the folio. > > > > This patch introduces a new type for guest_memfd folios, which > > isn't activated in this series but is here as a placeholder and > > to facilitate the code in the next patch. This will be used in > > the future to register a callback that informs the guest_memfd > > subsystem when the last reference is dropped, therefore knowing > > that the host doesn't have any remaining references. > > > > Signed-off-by: Fuad Tabba > > --- > > [...] > > > static const char *page_type_name(unsigned int page_type) > > diff --git a/mm/swap.c b/mm/swap.c > > index 47bc1bb919cc..241880a46358 100644 > > --- a/mm/swap.c > > +++ b/mm/swap.c > > @@ -38,6 +38,10 @@ > > #include > > #include > > > > +#ifdef CONFIG_KVM_GMEM_SHARED_MEM > > +#include > > +#endif > > + > > #include "internal.h" > > > > #define CREATE_TRACE_POINTS > > @@ -101,6 +105,11 @@ static void free_typed_folio(struct folio *folio) > > case PGTY_hugetlb: > > free_huge_folio(folio); > > return; > > +#endif > > +#ifdef CONFIG_KVM_GMEM_SHARED_MEM > > + case PGTY_guestmem: > > + kvm_gmem_handle_folio_put(folio); > > + return; > > Hm, if KVM is built as a module, will that work? Or would we need the > core-mm guest_memfd shim that would always be compiled into the core and > decouple KVM from guest_memfd ("library")? I'd assumed that it would work, since the module would have been loaded before this could trigger, but I guess I was wrong. Can you point me to an example of a similar shim in the core code, for me to add on the respin? Thanks, /fuad > -- > Cheers, > > David / dhildenb >