linux-kernel - Re: [PATCH v4 0/4] Add throttling detection to sev-guest

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Date:   Thu, 27 Oct 2022 08:53:54 -0700
From:   Dionna Amalie Glaze <dionnaglaze@...gle.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        Ashish Kalra <Ashish.Kalra@....com>
Subject: Re: [PATCH v4 0/4] Add throttling detection to sev-guest

Pinging y'all in case you haven't seen v4 :)

On Mon, Oct 24, 2022 at 3:47 PM Dionna Glaze <dionnaglaze@...gle.com> wrote:
>
> 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 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@....com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Joerg Roedel <jroedel@...e.de>
> Cc: Peter Gonda <pgonda@...gle.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
>
> Signed-off-by: Dionna Glaze <dionnaglaze@...gle.com>
>
> Dionna Glaze (4):
>   ccp: Name -1 return value as SEV_RET_NO_FW_CALL
>   x86/sev: Change snp_guest_issue_request's fw_err
>   virt/coco/sev-guest: Remove err in handle_guest_request
>   virt/coco/sev-guest: interpret VMM errors from guest request
>
>  arch/x86/include/asm/sev.h              |  4 +-
>  arch/x86/kernel/sev.c                   | 10 ++--
>  drivers/crypto/ccp/sev-dev.c            |  2 +-
>  drivers/virt/coco/sev-guest/sev-guest.c | 61 ++++++++++++++++++++-----
>  include/uapi/linux/psp-sev.h            |  7 +++
>  include/uapi/linux/sev-guest.h          | 18 +++++++-
>  6 files changed, 82 insertions(+), 20 deletions(-)
>
> --
> 2.38.0.135.g90850a2211-goog
>


-- 
-Dionna Glaze, PhD (she/her)