[PATCH v9 0/4] Add throttling detection to sev-guest

Dionna Glaze
2022-12-07T01:02:26Z

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 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

Cc: Tom Lendacky <Thomas.Lendacky@amd.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Peter Gonda <pgonda@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>

Signed-off-by: Dionna Glaze <dionnaglaze@google.com>

Dionna Glaze (3):
x86/sev: Change snp_guest_issue_request's fw_err
virt: sev-guest: Remove err in handle_guest_request
virt: sev-guest: interpret VMM errors from guest request

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.h | 4 +-
arch/x86/kernel/sev.c | 10 ++--
drivers/crypto/ccp/sev-dev.c | 22 ++++---
drivers/virt/coco/sev-guest/sev-guest.c | 76 +++++++++++++++++--------
include/uapi/linux/psp-sev.h | 7 +++
include/uapi/linux/sev-guest.h | 18 +++++-
7 files changed, 112 insertions(+), 46 deletions(-)