[PATCH v14 0/3] Add throttling detection to sev-guest

[Dionna Glaze]

The guest request synchronous API from SEV-SNP VMs to the host's security
processor consumes a global resource. For this reason, AMD's docs
recommend that the host implements a throttling mechanism. In order for
the guest to know it's been throttled and should try its request again,
we need some good-faith communication from the host that the request
has been throttled.

These patches work with the existing /dev/sev-guest ABI to detect a
throttling code.

Changes from v13:
  * Added double-buffering fix to the "Fixes" patch to address a secondary
    concern of zero trust with respect to host access to intermediate
    cryptographic computations in shared memory.
  * Removed module parameters and rate limiting in favor of just
    cond_resched.
  * Removed possible infinite loop of retries by giving up with an erased
    VMPCK and -ETIMEDOUT error after 60 seconds of retries.
Changes from v12:
  * Reordered fix patch to the beginning and kept it minimal.
  * Changed documentation in same patch as the respective change to the
    header.
  * Changed exitinfo2 in dev_alert to print in hex.
Changes from v11:
  * Squashed all type changing patches into 1 that modifies both sev-guest
    and x86/kernel/sev.c.
  * Removed fw_err field from sev-guest command struct (renamed exitinfo2).
Changes from v10:
  * Added sev_guestreq_err_t typedef early in chain to change a signature
    acress x86/sev and virt/coco/sev-guest in a single change. This makes
    all patches build. I have 3 cleanup patches to change the type and
    subsequently remove the typedef.
  * Changed exitinfo2 initial undefined value back to 0xff since Thomas
    indicated that a firmware error is only 16 bits.
Changes from v9:
  * Rebased on v6.2-rc3
Changes from v8:
  * Added documentation changes.
  * Changed commit messages to use passive voice.
  * Simplified control flow for __sev_platform_init_locked.
Changes from v7:
  * Replaced handle_guest_request arguments msg_ver and fw_err with a
    pointer to the snp_guest_request_ioctl argument struct.
Changes from v6:
  * Rebased on the IV reuse fix patch
  * renamed rate_hz to rate_s and fixed its MODULE_PARM_DESC to use the
    correct variable name.
  * Changed sleep_timeout_interrutible (not defined) to
    schedule_timeout_interruptible.
Changes from v5:
  * Fixed commit prefix text
  * Added all get_maintainers.pl folks to commits' Cc tags
  * Changed SET_RET_NO_FW_CALL commit's metadata to show pgonda signs
    off and is the author.
Changes from v4:
  * Clarified comment on SEV_RET_NO_FW_CALL
  * Changed ratelimit loop to use sleep_timeout_interruptible
Changes from v3:
  * sev-guest ratelimits itself to one request twice a second.
  * Fixed a type signature to use u64 instead of unsigned int
  * Set *exitinfo2 unconditionally after the ghcb_hv_call.
Changes from v2:
  * Codified the non-firmware-call firmware error code as (u32)-1.
  * Changed sev_issue_guest_request unsigned long *fw_err argument to
    u64 *exitinfo2 to more accurately and type-safely describe the
    value that it outputs.
  * Changed sev_issue_guest_request to always set its exitinfo2
    argument to either the non-firmware-call error code, the
    EXIT_INFO_2 returned from the VMM if the request failed, or 0 on
    success. This fixes a bug that returned uninitialized kernel stack
    memory to the user when there is no error.
  * Changed the throttle behavior to retry in the driver instead of
    returning -EAGAIN, due to possible message sequence number reuse
    on different message contents.

Changes from v1:
  * Changed throttle error code to 2

Dionna Glaze (2):
  virt/coco/sev-guest: Add throttling awareness
  x86/sev: Change snp_guest_issue_request's fw_err

Peter Gonda (1):
  crypto: ccp - Name -1 return value as SEV_RET_NO_FW_CALL

 Documentation/virt/coco/sev-guest.rst   | 21 ++++--
 arch/x86/include/asm/sev-common.h       |  3 -
 arch/x86/include/asm/sev.h              |  4 +-
 arch/x86/kernel/sev.c                   | 13 ++--
 drivers/crypto/ccp/sev-dev.c            | 22 +++---
 drivers/virt/coco/sev-guest/sev-guest.c | 95 +++++++++++++++++--------
 include/uapi/linux/psp-sev.h            |  7 ++
 include/uapi/linux/sev-guest.h          | 18 ++++-
 8 files changed, 127 insertions(+), 56 deletions(-)

-- 
2.39.1.581.gbfd45094c4-goog