On Tue, May 12, 2026, Fuad Tabba wrote: > On Mon, 11 May 2026 at 21:25, Sean Christopherson <[email protected]> wrote: > > > I used kvm_vm_release() because it's the only public API that closes > > > vm->fd to trigger kernel-side destruction. But the existing callers > > > follow it with vm_recreate_with_one_vcpu(), so the "release + later > > > kvm_vm_free()" path isn't exercised today. > > > > > > I see three ways to make this clean: > > > a) This patch: kvm_vm_release() becomes idempotent for its three > > > FDs, matching the kvm_stats_release() idiom it already invokes. > > > b) Leave kvm_vm_release() as-is and add a dedicated helper, e.g. > > > kvm_vm_destroy_kernel(), that closes vm->fd to trigger kernel > > > destruction while leaving the kvm_vm struct intact for > > > post-destruction inspection. kvm_vm_free() learns to handle the > > > half-released state. > > > c) Something else entirely, e.g., the test should manage vm->fd > > > directly and not rely on library helpers for this pattern. > > > > d) Fully kill the VM; validate the semantics with an explict mmap(). > > > > The entire point of the test you are writing is to verfiy that a > > guest_memfd VMA > > doesn't somehow cause KVM to leak state. So, make that obvious instead of > > abusing > > APIs that kinda sorta do what you want, but not really. > > > > mem = kvm_mmap(region->mmap_size, PROT_READ | PROT_WRITE, > > MAP_SHARED, > > region->guest_memfd); > > > > ... > > > > kvm_vm_free(vm); > > > > TEST_ASSERT(is_zero(mem, ...)); > > The test isn't about guest_memfd. The pKVM support that just landed > via Will's series [1]
Landed where? Is pKVM actually going upstream with anonymous memory? I thought the inability to protect against page faults in the untrusted kernel was a non-starter? > kvm_mmap() + kvm_vm_free() + is_zero() doesn't translate here. The only > host view of the donated pages is the memslot mmap, and kvm_vm_free() > munmaps it on the way out, so inspection has to happen between > kernel-side destruction and userspace free. kvm_vm_release() is the > only library primitive that does that today. > > What do you suggest? Manually allocate the memory and expose it to the guest via vm_set_user_memory_region2() vm_set_user_memory_region().
