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AJvYcCUKs0Q6/cBbjkOQlg15zNXEU917rbh4jR7pkW8LK0tkdZz0L0sMLUtcI3UOX+u1PYSAjMk=@vger.kernel.org X-Gm-Message-State: AOJu0YxuqTo4mISlGlK07RzsiN/nDc57pR5CzBUXRTOJI3XlB8Jfh+ht EZnu5eyV/gEw80zt7axpvtqxtem9YnHHE5XkRZ2PurJTbCtpbXHgkR1OhGsshK+q9OR6acIAEpd ojL7BZpMkw3vbBfDghA== X-Google-Smtp-Source: AGHT+IEsH4AhFxEPswA6HSpr3bvQoscIWPYhswjH6B0ZmAUwG6NVAuJoyTvkHIFeYc2jG+fxyhqARW7A5Wn5aFvO X-Received: from uabib8.prod.google.com ([2002:a05:6130:1c88:b0:85b:d490:f925]) (user=jthoughton job=prod-delivery.src-stubby-dispatcher) by 2002:a05:620a:2685:b0:7a9:acd5:1b21 with SMTP id af79cd13be357-7b6a61cb6e2mr738681685a.50.1733339656100; Wed, 04 Dec 2024 11:14:16 -0800 (PST) Date: Wed, 4 Dec 2024 19:13:36 +0000 In-Reply-To: <20241204191349.1730936-1-jthoughton@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241204191349.1730936-1-jthoughton@google.com> X-Mailer: git-send-email 2.47.0.338.g60cca15819-goog Message-ID: <20241204191349.1730936-2-jthoughton@google.com> Subject: [PATCH v1 01/13] KVM: Add KVM_MEM_USERFAULT memslot flag and bitmap From: James Houghton To: Paolo Bonzini , Sean Christopherson Cc: Jonathan Corbet , Marc Zyngier , Oliver Upton , Yan Zhao , James Houghton , Nikita Kalyazin , Anish Moorthy , Peter Gonda , Peter Xu , David Matlack , Wang@google.com, Wei W , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev Use one of the 14 reserved u64s in struct kvm_userspace_memory_region2 for the user to provide `userfault_bitmap`. The memslot flag indicates if KVM should be reading from the `userfault_bitmap` field from the memslot. The user is permitted to provide a bogus pointer. If the pointer cannot be read from, we will return -EFAULT (with no other information) back to the user. Signed-off-by: James Houghton --- include/linux/kvm_host.h | 14 ++++++++++++++ include/uapi/linux/kvm.h | 4 +++- virt/kvm/Kconfig | 3 +++ virt/kvm/kvm_main.c | 28 ++++++++++++++++++++++++++++ 4 files changed, 48 insertions(+), 1 deletion(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 401439bb21e3..f7a3dfd5e224 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -590,6 +590,7 @@ struct kvm_memory_slot { unsigned long *dirty_bitmap; struct kvm_arch_memory_slot arch; unsigned long userspace_addr; + unsigned long __user *userfault_bitmap; u32 flags; short id; u16 as_id; @@ -724,6 +725,11 @@ static inline bool kvm_arch_has_readonly_mem(struct kvm *kvm) } #endif +static inline bool kvm_has_userfault(struct kvm *kvm) +{ + return IS_ENABLED(CONFIG_HAVE_KVM_USERFAULT); +} + struct kvm_memslots { u64 generation; atomic_long_t last_used_slot; @@ -2553,4 +2559,12 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, struct kvm_pre_fault_memory *range); #endif +int kvm_gfn_userfault(struct kvm *kvm, struct kvm_memory_slot *memslot, + gfn_t gfn); + +static inline bool kvm_memslot_userfault(struct kvm_memory_slot *memslot) +{ + return memslot->flags & KVM_MEM_USERFAULT; +} + #endif diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 502ea63b5d2e..94be7e8b46a4 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -40,7 +40,8 @@ struct kvm_userspace_memory_region2 { __u64 guest_memfd_offset; __u32 guest_memfd; __u32 pad1; - __u64 pad2[14]; + __u64 userfault_bitmap; + __u64 pad2[13]; }; /* @@ -51,6 +52,7 @@ struct kvm_userspace_memory_region2 { #define KVM_MEM_LOG_DIRTY_PAGES (1UL << 0) #define KVM_MEM_READONLY (1UL << 1) #define KVM_MEM_GUEST_MEMFD (1UL << 2) +#define KVM_MEM_USERFAULT (1UL << 3) /* for KVM_IRQ_LINE */ struct kvm_irq_level { diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig index 54e959e7d68f..9eb1fae238b1 100644 --- a/virt/kvm/Kconfig +++ b/virt/kvm/Kconfig @@ -124,3 +124,6 @@ config HAVE_KVM_ARCH_GMEM_PREPARE config HAVE_KVM_ARCH_GMEM_INVALIDATE bool depends on KVM_PRIVATE_MEM + +config HAVE_KVM_USERFAULT + bool diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index de2c11dae231..23fa3e911c4e 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1541,6 +1541,9 @@ static int check_memory_region_flags(struct kvm *kvm, !(mem->flags & KVM_MEM_GUEST_MEMFD)) valid_flags |= KVM_MEM_READONLY; + if (kvm_has_userfault(kvm)) + valid_flags |= KVM_MEM_USERFAULT; + if (mem->flags & ~valid_flags) return -EINVAL; @@ -2042,6 +2045,8 @@ int __kvm_set_memory_region(struct kvm *kvm, if (r) goto out; } + if (mem->flags & KVM_MEM_USERFAULT) + new->userfault_bitmap = (unsigned long *)mem->userfault_bitmap; r = kvm_set_memslot(kvm, old, new, change); if (r) @@ -6426,3 +6431,26 @@ void kvm_exit(void) kvm_irqfd_exit(); } EXPORT_SYMBOL_GPL(kvm_exit); + +int kvm_gfn_userfault(struct kvm *kvm, struct kvm_memory_slot *memslot, + gfn_t gfn) +{ + unsigned long bitmap_chunk = 0; + off_t offset; + + if (!kvm_memslot_userfault(memslot)) + return 0; + + if (WARN_ON_ONCE(!memslot->userfault_bitmap)) + return 0; + + offset = gfn - memslot->base_gfn; + + if (copy_from_user(&bitmap_chunk, + memslot->userfault_bitmap + offset / BITS_PER_LONG, + sizeof(bitmap_chunk))) + return -EFAULT; + + /* Set in the bitmap means that the gfn is userfault */ + return !!(bitmap_chunk & (1ul << (offset % BITS_PER_LONG))); +}