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Fri, 07 Mar 2025 00:57:38 -0800 (PST) MIME-Version: 1.0 References: <20250303171013.3548775-4-tabba@google.com> In-Reply-To: From: Fuad Tabba Date: Fri, 7 Mar 2025 08:57:00 +0000 X-Gm-Features: AQ5f1JpvWVX4p-I-6NV1AGFD4gCusH1RF5PO6B8I5VhGtEmyhDA3YIF8HF36ulc Message-ID: Subject: Re: [PATCH v5 3/9] KVM: guest_memfd: Allow host to map guest_memfd() pages To: Ackerley Tng 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, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@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, 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, peterx@redhat.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 38FB840006 X-Rspam-User: X-Stat-Signature: 9ffn855r1j7tr86fs1m5yudnkip95j4n X-HE-Tag: 1741337859-556455 X-HE-Meta: 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 eL+c21/j xeENgnYPk7uKAWwcmyIpuplBjcnxIDhH+FE3rjQ8gyuvCo1AvIcjvm2UghthvbEDNZkUP+O1ugR+O7CiQA+n099H2xD7hcJJmQskWcHpt7I9GAUqfPdlNOIzfpDdRaClFRF3nKD2CFFzP9/8A0z5W3kOYL5T28BnV1s/nyagzOziVIrklpz+i42T7Y5vMWjYtY8pe+iVCQg2fBoY8AQbYtBQv2rkei7ki78ivzyHTKLuFG8H8kpU0gYGn9kzKJd0szWl+irKAKDI64VDHhxrhB48QTJK572hhoHUKVx/8H80srfsqb7OF81S+i5EDjnHTnLvMukgwAIUvpCXnotMdlJDLIA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000046, 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 Ackerley, On Thu, 6 Mar 2025 at 22:46, Ackerley Tng wrote: > > Fuad Tabba writes: > > > 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. > > > > Also add the KVM capability KVM_CAP_GMEM_SHARED_MEM, which > > indicates that the VM supports shared memory in guest_memfd, or > > that the host can create VMs that support shared memory. > > Supporting shared memory implies that memory can be mapped when > > shared with the host. > > > > This is controlled by the KVM_GMEM_SHARED_MEM configuration > > option. > > > > Signed-off-by: Fuad Tabba > > --- > > include/linux/kvm_host.h | 11 ++++ > > include/uapi/linux/kvm.h | 1 + > > virt/kvm/guest_memfd.c | 105 +++++++++++++++++++++++++++++++++++++++ > > virt/kvm/kvm_main.c | 4 ++ > > 4 files changed, 121 insertions(+) > > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > index 7788e3625f6d..2d025b8ee20e 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) > > Is this a copypasta error? I'm wondering if this should be > !IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM). Yes. Kirill had pointed that out as well. I will fix it. > Also, would you consider defining a __weak function to be overridden by > different architectures, or would weak symbols not be inline-able? I have no strong opinion, but I think that it should follow the same pattern as kvm_arch_has_private_mem(). Cheers, /fuad > > +static inline bool kvm_arch_gmem_supports_shared_mem(struct kvm *kvm) > > +{ > > + return false; > > +} > > +#endif > > + > > > >