Re: [PATCH v6 4/8] KVM: Extend the memslot to support fd-based private memory
From: Sean Christopherson <seanjc@google.com>
Date: 2022-06-17 20:52:22
Also in:
kvm, linux-doc, linux-fsdevel, linux-mm, lkml, qemu-devel
Subsystem:
kernel virtual machine (kvm), the rest · Maintainers:
Paolo Bonzini, Linus Torvalds
On Thu, May 19, 2022, Chao Peng wrote:
quoted hunk ↗ jump to hunk
@@ -653,12 +662,12 @@ struct kvm_irq_routing_table { }; #endif -#ifndef KVM_PRIVATE_MEM_SLOTS -#define KVM_PRIVATE_MEM_SLOTS 0 +#ifndef KVM_INTERNAL_MEM_SLOTS +#define KVM_INTERNAL_MEM_SLOTS 0 #endif
This rename belongs in a separate patch.
quoted hunk ↗ jump to hunk
#define KVM_MEM_SLOTS_NUM SHRT_MAX -#define KVM_USER_MEM_SLOTS (KVM_MEM_SLOTS_NUM - KVM_PRIVATE_MEM_SLOTS) +#define KVM_USER_MEM_SLOTS (KVM_MEM_SLOTS_NUM - KVM_INTERNAL_MEM_SLOTS) #ifndef __KVM_VCPU_MULTIPLE_ADDRESS_SPACE static inline int kvm_arch_vcpu_memslots_id(struct kvm_vcpu *vcpu)@@ -1087,9 +1096,9 @@ enum kvm_mr_change { }; int kvm_set_memory_region(struct kvm *kvm, - const struct kvm_userspace_memory_region *mem); + const struct kvm_user_mem_region *mem); int __kvm_set_memory_region(struct kvm *kvm, - const struct kvm_userspace_memory_region *mem); + const struct kvm_user_mem_region *mem); void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot); void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen); int kvm_arch_prepare_memory_region(struct kvm *kvm,diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index e10d131edd80..28cacd3656d4 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h@@ -103,6 +103,29 @@ struct kvm_userspace_memory_region { __u64 userspace_addr; /* start of the userspace allocated memory */ }; +struct kvm_userspace_memory_region_ext { + struct kvm_userspace_memory_region region; + __u64 private_offset; + __u32 private_fd; + __u32 pad1; + __u64 pad2[14]; +}; + +#ifdef __KERNEL__ +/* Internal helper, the layout must match above user visible structures */
It's worth explicity calling out which structureso this aliases. And rather than add a comment about the layout needing to match that, enforce it in code. I personally wouldn't bother with an expolicit comment about the layout, IMO that's a fairly obvious implication of aliasing. /* * kvm_user_mem_region is a kernel-only alias of kvm_userspace_memory_region_ext * that "unpacks" kvm_userspace_memory_region so that KVM can directly access * all fields from the top-level "extended" region. */ And I think it's in this patch that you missed a conversion to the alias, in the prototype for check_memory_region_flags() (looks like it gets fixed up later in the series).
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 0f81bf0407be..8765b334477d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c@@ -1466,7 +1466,7 @@ static void kvm_replace_memslot(struct kvm *kvm, } } -static int check_memory_region_flags(const struct kvm_userspace_memory_region *mem) +static int check_memory_region_flags(const struct kvm_user_mem_region *mem) { u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
@@ -4514,6 +4514,33 @@ static int kvm_vm_ioctl_get_stats_fd(struct kvm *kvm) return fd; } +#define SANITY_CHECK_MEM_REGION_FIELD(field) \ +do { \ + BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) != \ + offsetof(struct kvm_userspace_memory_region, field)); \ + BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) != \ + sizeof_field(struct kvm_userspace_memory_region, field)); \ +} while (0) + +#define SANITY_CHECK_MEM_REGION_EXT_FIELD(field) \ +do { \ + BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) != \ + offsetof(struct kvm_userspace_memory_region_ext, field)); \ + BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) != \ + sizeof_field(struct kvm_userspace_memory_region_ext, field)); \ +} while (0) + +static void kvm_sanity_check_user_mem_region_alias(void) +{ + SANITY_CHECK_MEM_REGION_FIELD(slot); + SANITY_CHECK_MEM_REGION_FIELD(flags); + SANITY_CHECK_MEM_REGION_FIELD(guest_phys_addr); + SANITY_CHECK_MEM_REGION_FIELD(memory_size); + SANITY_CHECK_MEM_REGION_FIELD(userspace_addr); + SANITY_CHECK_MEM_REGION_EXT_FIELD(private_offset); + SANITY_CHECK_MEM_REGION_EXT_FIELD(private_fd); +} + static long kvm_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg) {
@@ -4541,6 +4568,8 @@ static long kvm_vm_ioctl(struct file *filp, unsigned long size; u32 flags; + kvm_sanity_check_user_mem_region_alias(); + memset(&mem, 0, sizeof(mem)); r = -EFAULT;
quoted hunk ↗ jump to hunk
+struct kvm_user_mem_region { + __u32 slot; + __u32 flags; + __u64 guest_phys_addr; + __u64 memory_size; + __u64 userspace_addr; + __u64 private_offset; + __u32 private_fd; + __u32 pad1; + __u64 pad2[14]; +}; +#endif + /* * The bit 0 ~ bit 15 of kvm_memory_region::flags are visible for userspace, * other bits are reserved for kvm internal use which are defined in@@ -110,6 +133,7 @@ struct kvm_userspace_memory_region { */ #define KVM_MEM_LOG_DIRTY_PAGES (1UL << 0) #define KVM_MEM_READONLY (1UL << 1) +#define KVM_MEM_PRIVATE (1UL << 2)
Hmm, KVM_MEM_PRIVATE is technically wrong now that a "private" memslot maps private and/or shared memory. Strictly speaking, we don't actually need a new flag. Valid file descriptors must be >=0, so the logic for specifying a memslot that can be converted between private and shared could be that "(int)private_fd < 0" means "not convertible", i.e. derive the flag from private_fd. And looking at the two KVM consumers of the flag, via kvm_slot_is_private(), they're both wrong. Both kvm_faultin_pfn() and kvm_mmu_max_mapping_level() should operate on the _fault_, not the slot. So it would actually be a positive to not have an easy way to query if a slot supports conversion.
/* for KVM_IRQ_LINE */
struct kvm_irq_level {...
+ if (flags & KVM_MEM_PRIVATE) {An added bonus of dropping KVM_MEM_PRIVATE is that these checks go away.
+ r = -EINVAL;
+ goto out;
+ }
+
+ size = sizeof(struct kvm_userspace_memory_region);
+
+ if (copy_from_user(&mem, argp, size))
+ goto out;
+
+ r = -EINVAL;
+ if ((flags ^ mem.flags) & KVM_MEM_PRIVATE)
goto out;
- r = kvm_vm_ioctl_set_memory_region(kvm, &kvm_userspace_mem);
+ r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
break;
}
case KVM_GET_DIRTY_LOG: {
--
2.25.1