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SubjectRe: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE
On Fri, Dec 02, 2022, Chao Peng wrote:
> @@ -10357,6 +10364,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>
> if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
> static_call(kvm_x86_update_cpu_dirty_logging)(vcpu);
> +
> + if (kvm_check_request(KVM_REQ_MEMORY_MCE, vcpu)) {
> + vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;

Synthesizing triple fault shutdown is not the right approach. Even with TDX's
MCE "architecture" (heavy sarcasm), it's possible that host userspace and the
guest have a paravirt interface for handling memory errors without killing the
host.

> + r = 0;
> + goto out;
> + }
> }


> @@ -1982,6 +2112,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
> !access_ok((void __user *)(unsigned long)mem->userspace_addr,
> mem->memory_size))
> return -EINVAL;
> + if (mem->flags & KVM_MEM_PRIVATE &&
> + (mem->restricted_offset & (PAGE_SIZE - 1) ||

Align indentation.

> + mem->restricted_offset > U64_MAX - mem->memory_size))

Strongly prefer to use similar logic to existing code that detects wraps:

mem->restricted_offset + mem->memory_size < mem->restricted_offset

This is also where I'd like to add the "gfn is aligned to offset" check, though
my brain is too fried to figure that out right now.

> + return -EINVAL;
> if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
> return -EINVAL;
> if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> @@ -2020,6 +2154,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
> if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
> return -EINVAL;
> } else { /* Modify an existing slot. */
> + /* Private memslots are immutable, they can only be deleted. */

I'm 99% certain I suggested this, but if we're going to make these memslots
immutable, then we should straight up disallow dirty logging, otherwise we'll
end up with a bizarre uAPI.

> + if (mem->flags & KVM_MEM_PRIVATE)
> + return -EINVAL;
> if ((mem->userspace_addr != old->userspace_addr) ||
> (npages != old->npages) ||
> ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
> @@ -2048,10 +2185,28 @@ int __kvm_set_memory_region(struct kvm *kvm,
> new->npages = npages;
> new->flags = mem->flags;
> new->userspace_addr = mem->userspace_addr;
> + if (mem->flags & KVM_MEM_PRIVATE) {
> + new->restricted_file = fget(mem->restricted_fd);
> + if (!new->restricted_file ||
> + !file_is_restrictedmem(new->restricted_file)) {
> + r = -EINVAL;
> + goto out;
> + }
> + new->restricted_offset = mem->restricted_offset;
> + }
> +
> + new->kvm = kvm;

Set this above, just so that the code flows better.

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