On 2/24/21 9:44 PM, Steve Rutherford wrote:
On Wed, Feb 24, 2021 at 1:00 AM Nathan Tempelman <natet@xxxxxxxxxx> wrote:@@ -1186,6 +1195,10 @@ int svm_register_enc_region(struct kvm *kvm, if (!sev_guest(kvm)) return -ENOTTY; + /* If kvm is mirroring encryption context it isn't responsible for it */ + if (is_mirroring_enc_context(kvm)) + return -ENOTTY; +Is this necessary? Same for unregister. When we looked at sev_pin_memory, I believe we concluded that double pinning was safe.if (range->addr > ULONG_MAX || range->size > ULONG_MAX) return -EINVAL; @@ -1252,6 +1265,10 @@ int svm_unregister_enc_region(struct kvm *kvm, struct enc_region *region; int ret; + /* If kvm is mirroring encryption context it isn't responsible for it */ + if (is_mirroring_enc_context(kvm)) + return -ENOTTY; + mutex_lock(&kvm->lock); if (!sev_guest(kvm)) { @@ -1282,6 +1299,65 @@ int svm_unregister_enc_region(struct kvm *kvm, return ret; } +int svm_vm_copy_asid_to(struct kvm *kvm, unsigned int mirror_kvm_fd) +{ + struct file *mirror_kvm_file; + struct kvm *mirror_kvm; + struct kvm_sev_info *mirror_kvm_sev; + unsigned int asid; + int ret; + + if (!sev_guest(kvm)) + return -ENOTTY;You definitely don't want this: this is the function that turns the vm into an SEV guest (marks SEV as active).
The sev_guest() function does not set sev->active, it only checks it. The sev_guest_init() function is where sev->active is set.
(Not an issue with this patch, but a broader issue) I believe sev_guest lacks the necessary acquire/release barriers on sev->active,
The svm_mem_enc_op() takes the kvm lock and that is the only way into the sev_guest_init() function where sev->active is set.
Thanks, Tom
since it's called without the kvm lock. I mean, it's x86, so the only one that's going to hose you is the compiler for this type of access. There should be an smp_rmb() after the access in sev_guest and an smp_wmb() before the access in SEV_GUEST_INIT and here.+ + mutex_lock(&kvm->lock); + + /* Mirrors of mirrors should work, but let's not get silly */ + if (is_mirroring_enc_context(kvm)) { + ret = -ENOTTY; + goto failed; + } + + mirror_kvm_file = fget(mirror_kvm_fd); + if (!kvm_is_kvm(mirror_kvm_file)) { + ret = -EBADF; + goto failed; + } + + mirror_kvm = mirror_kvm_file->private_data; + + if (mirror_kvm == kvm || is_mirroring_enc_context(mirror_kvm)) {Just check if the source is an sev_guest and that the destination is not an sev_guest. I reviewed earlier incarnations of this, and think the high-level idea is sound. I'd like to see kvm-selftests for this patch, and plan on collaborating with AMD to help make those happen.
