On 03/16/2017 05:38 AM, Paolo Bonzini wrote:
On 02/03/2017 16:18, Brijesh Singh wrote:
The SEV memory encryption engine uses a tweak such that two identical
plaintexts at different location will have a different ciphertexts.
So swapping or moving ciphertexts of two pages will not result in
plaintexts being swapped. Relocating (or migrating) a physical backing pages
for SEV guest will require some additional steps. The current SEV key
management spec [1] does not provide commands to swap or migrate (move)
ciphertexts. For now we pin the memory allocated for the SEV guest. In
future when SEV key management spec provides the commands to support the
page migration we can update the KVM code to remove the pinning logical
without making any changes into userspace (qemu).
The patch pins userspace memory when a new slot is created and unpin the
memory when slot is removed.
[1] http://support.amd.com/TechDocs/55766_SEV-KM%20API_Spec.pdf
This is not enough, because memory can be hidden temporarily from the
guest and remapped later. Think of a PCI BAR that is backed by RAM, or
also SMRAM. The pinning must be kept even in that case.
You need to add a pair of KVM_MEMORY_ENCRYPT_OPs (one that doesn't map
to a PSP operation), such as KVM_REGISTER/UNREGISTER_ENCRYPTED_RAM. In
QEMU you can use a RAMBlockNotifier to invoke the ioctls.
I was hoping to avoid adding new ioctl, but I see your point. Will add a pair of ioctl's
and use RAMBlocNotifier to invoke those ioctls.
-Brijesh
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