KVM: SEV: Acquire vcpu mutex when updating VMSA

KVM: SEV: Acquire vcpu mutex when updating VMSA

The update-VMSA ioctl touches data stored in struct kvm_vcpu, and
therefore should not be performed concurrently with any VCPU ioctl
that might cause KVM or the processor to use the same data.

Adds vcpu mutex guard to the VMSA updating code. Refactors out
__sev_launch_update_vmsa() function to deal with per vCPU parts
of sev_launch_update_vmsa().

Fixes: ad73109ae7ec ("KVM: SVM: Provide support to launch and run an SEV-ES guest")
Signed-off-by: Peter Gonda <[email protected]>
Cc: Marc Orr <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Sean Christopherson <[email protected]>
Cc: Brijesh Singh <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Message-Id: <20210915171755.3773766[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>