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AJvYcCVWc3TSogiBCQGfcl+wuB+83zIoIWxb8w/A6rD8mhNnoTkr57wwS8CvSVqhutFv8zG2ExWmOGyptg==@kvack.org X-Gm-Message-State: AOJu0Yy1FsTIgIzhWIZkFyOP3oQ1XnAYh5UrutxN4lACKx4OI6eNT8wT yYJFikZwYtpqyvEFaZClqSgi6SsgrLvgW/L0+Jd0ut7pbM6pK2O49nrI4rSt330GrLX60+zEuSS KgY/ONpmpxZoFMrm1gs68nw== X-Google-Smtp-Source: AGHT+IH1gv4RpFaDlQVit34hQ/BYrbtXVH0HRGTDjEqwVYkLbSyXOxx+M0Wdxyv5Mv70FNiqko9tqyIjIcC3tcU0Ug== X-Received: from pfbdu11.prod.google.com ([2002:a05:6a00:2b4b:b0:730:90b2:dab]) (user=ackerleytng job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:324c:b0:73e:23bd:fb9c with SMTP id d2e1a72fcca58-74058b1fd67mr4595140b3a.23.1746223604596; Fri, 02 May 2025 15:06:44 -0700 (PDT) Date: Fri, 02 May 2025 15:06:43 -0700 In-Reply-To: Mime-Version: 1.0 References: <20250430165655.605595-1-tabba@google.com> <20250430165655.605595-9-tabba@google.com> Message-ID: Subject: Re: [PATCH v8 08/13] KVM: guest_memfd: Allow host to map guest_memfd() pages From: Ackerley Tng To: David Hildenbrand , 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, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@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, peterx@redhat.com, pankaj.gupta@amd.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: C0B57180007 X-Stat-Signature: zx75jaqndsya4jcmgs1knjfr19cjuhhz X-Rspam-User: X-HE-Tag: 1746223605-372615 X-HE-Meta: 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 J8Uo26rK 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 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: David Hildenbrand writes: > On 30.04.25 18:56, 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. 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. >> >> This patch introduces the configuration option KVM_GMEM_SHARED_MEM, >> which enables support for in-place shared memory. >> >> It also introduces the KVM capability KVM_CAP_GMEM_SHARED_MEM, which >> indicates that the host can create VMs that support shared memory. >> Supporting shared memory implies that memory can be mapped when shared >> with the host. >> >> Signed-off-by: Fuad Tabba >> --- >> include/linux/kvm_host.h | 15 ++++++- >> include/uapi/linux/kvm.h | 1 + >> virt/kvm/Kconfig | 5 +++ >> virt/kvm/guest_memfd.c | 92 ++++++++++++++++++++++++++++++++++++++++ >> virt/kvm/kvm_main.c | 4 ++ >> 5 files changed, 116 insertions(+), 1 deletion(-) >> >> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h >> index 9419fb99f7c2..f3af6bff3232 100644 >> --- a/include/linux/kvm_host.h >> +++ b/include/linux/kvm_host.h >> @@ -729,6 +729,17 @@ static inline bool kvm_arch_supports_gmem(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_GMEM_SHARED_MEM) >> +static inline bool kvm_arch_gmem_supports_shared_mem(struct kvm *kvm) >> +{ >> + return false; >> +} >> +#endif >> + >> #ifndef kvm_arch_has_readonly_mem >> static inline bool kvm_arch_has_readonly_mem(struct kvm *kvm) >> { >> @@ -2516,7 +2527,9 @@ static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn) >> >> static inline bool kvm_mem_from_gmem(struct kvm *kvm, gfn_t gfn) >> { >> - /* For now, only private memory gets consumed from guest_memfd. */ >> + if (kvm_arch_gmem_supports_shared_mem(kvm)) >> + return true; > > After our discussion yesterday, am I correct that we will not be > querying the KVM capability, but instead the "SHARED_TRACKING" (or > however that flag is called) on the underlying guest_memfd instead? > > I assume the function would then look something like > > if (!kvm_supports_gmem(kvm)) > return false; > if (kvm_arch_gmem_supports_shared_mem(kvm)) > return .. TBD, test the gmem flag for the slot via gfn > return kvm_mem_is_private(kvm, gfn); > Yes, I believe we're aligned here. I added a patch that will do this, but it depends on other parts of the patch series and I think it's better if you review it altogether when Fuad posts it (as opposed to reviewing a snippet I drop here. >> + >> return kvm_mem_is_private(kvm, gfn); >> } >> >> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >> index b6ae8ad8934b..8bc8046c7f3a 100644 >> --- a/include/uapi/linux/kvm.h >> +++ b/include/uapi/linux/kvm.h >> @@ -930,6 +930,7 @@ struct kvm_enable_cap { >> #define KVM_CAP_X86_APIC_BUS_CYCLES_NS 237 >> #define KVM_CAP_X86_GUEST_MODE 238 >> #define KVM_CAP_ARM_WRITABLE_IMP_ID_REGS 239 >> +#define KVM_CAP_GMEM_SHARED_MEM 240 >> >> struct kvm_irq_routing_irqchip { >> __u32 irqchip; >> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig >> index 559c93ad90be..f4e469a62a60 100644 >> --- a/virt/kvm/Kconfig >> +++ b/virt/kvm/Kconfig >> @@ -128,3 +128,8 @@ config HAVE_KVM_ARCH_GMEM_PREPARE >> config HAVE_KVM_ARCH_GMEM_INVALIDATE >> bool >> depends on KVM_GMEM >> + >> +config KVM_GMEM_SHARED_MEM >> + select KVM_GMEM >> + bool >> + prompt "Enables in-place shared memory for guest_memfd" >> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c >> index 6db515833f61..8bc8fc991d58 100644 >> --- a/virt/kvm/guest_memfd.c >> +++ b/virt/kvm/guest_memfd.c >> @@ -312,7 +312,99 @@ 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 >> +/* >> + * Returns true if the folio is shared with the host and the guest. >> + */ >> +static bool kvm_gmem_offset_is_shared(struct file *file, pgoff_t index) >> +{ >> + struct kvm_gmem *gmem = file->private_data; >> + >> + /* For now, VMs that support shared memory share all their memory. */ >> + return kvm_arch_gmem_supports_shared_mem(gmem->kvm); > > Similar here: likely we want to check the guest_memfd flag. > > -- > Cheers, > > David / dhildenb