The GHCB specification recommends that SNP guest requests should be
rate limited. Add a command to permit the VMM to set the rate limit
on a per-VM scale.

The AMD-SP is a global resource that must be shared across VMs, so
its time should be multiplexed across VMs fairly. It is the
responsibility of the VMM to ensure all SEV-SNP VMs have a rate limit
set such that the collective set of VMs on the machine have a rate of
access that does not exceed the device's capacity.

The sev-guest device already respects the SNP_GUEST_VMM_ERR_BUSY
result code, so utilize that result to cause the guest to retry after
waiting momentarily.

Changes since v4:
  * Fixed build failure caused by rebase.
  * Added ratelimit.h include.
  * Added rate bounds checking to stay within ratelimit types.
Changes since v3:
  * Rebased on master, changed module parameter to mem_enc_ioctl
    command. Changed commit descriptions. Much time has passed.
Changes since v2:
  * Rebased on v7, changed "we" wording to passive voice.
Changes since v1:
  * Added missing Ccs to patches.

Dionna Glaze (2):
  kvm: sev: Add SEV-SNP guest request throttling
  kvm: sev: If ccp is busy, report busy to guest

 .../virt/kvm/x86/amd-memory-encryption.rst    | 23 +++++++++++
 arch/x86/include/uapi/asm/kvm.h               |  7 ++++
 arch/x86/kvm/svm/sev.c                        | 38 +++++++++++++++++++
 arch/x86/kvm/svm/svm.h                        |  3 ++
 4 files changed, 71 insertions(+)

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2.49.0.1101.gccaa498523-goog