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

From: Dionna Glaze
Date: Mon Feb 13 2023 - 12:25:46 EST


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