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5932ca411e
KVM_PRE_FAULT_MEMORY for an SNP guest can race with sev_gmem_post_populate() in bad ways. The following sequence for instance can potentially trigger an RMP fault: thread A, sev_gmem_post_populate: called thread B, sev_gmem_prepare: places below 'pfn' in a private state in RMP thread A, sev_gmem_post_populate: *vaddr = kmap_local_pfn(pfn + i); thread A, sev_gmem_post_populate: copy_from_user(vaddr, src + i * PAGE_SIZE, PAGE_SIZE); RMP #PF Fix this by only allowing KVM_PRE_FAULT_MEMORY to run after a guest's initial private memory contents have been finalized via KVM_SEV_SNP_LAUNCH_FINISH. Beyond fixing this issue, it just sort of makes sense to enforce this, since the KVM_PRE_FAULT_MEMORY documentation states: "KVM maps memory as if the vCPU generated a stage-2 read page fault" which sort of implies we should be acting on the same guest state that a vCPU would see post-launch after the initial guest memory is all set up. Co-developed-by: Michael Roth <michael.roth@amd.com> Signed-off-by: Michael Roth <michael.roth@amd.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>