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    SubjectRe: [PATCH Part2 v6 12/49] crypto: ccp: Add support to initialize the AMD-SP for SEV-SNP
    On Fri, Oct 14, 2022 at 04:09:11PM -0500, Kalra, Ashish wrote:
    > Yes, we need to do:
    >
    > wbinvd_on_all_cpus();
    > SNP_DF_FLUSH
    >
    > Need to ensure all the caches are clear before launching the first guest and
    > this has to be a combination of WBINVD and SNP_DF_FLUSH command.

    Ok.

    > > Why isn't this retval checked?
    >
    > From the SNP FW ABI specs, for the SNP_SHUTDOWN command:
    >
    > Firmware checks for every encryption capable ASID that the ASID is not in
    > use by a guest and a DF_FLUSH is not required. If a DF_FLUSH is required,
    > the firmware returns DFFLUSH_REQUIRED.
    >
    > Considering that SNP_SHUTDOWN command will check if DF_FLUSH was
    > required and if so, and not invoked before that command, returns
    > an error indicating that DFFLUSH is required.
    >
    > This way, we can cleverly avoid taking the error code path for
    > DF_FLUSH command here and instead let the SNP_SHUTDOWN command
    > failure below indicate if DF_FLUSH command failed.
    >
    > This also ensures that we always invoke SNP_SHUTDOWN command,
    > irrespective of SNP_DF_FLUSH command failure as SNP_DF_FLUSH may
    > actually not be required by the SHUTDOWN command.

    This all sounds just silly. The proper way to do this is:

    retry:
    ret = __sev_do_cmd_locked(SEV_CMD_SNP_SHUTDOWN, NULL, error);
    if (ret == DFFLUSH_REQUIRED) {
    ret = __sev_do_cmd_locked(SEV_CMD_SNP_DF_FLUSH, NULL, NULL);
    if (ret)
    "... DF_FLUSH failed...";

    goto retry;
    }

    I'm assuming here the firmware is smart enough to not keep returning
    DFFLUSH_REQUIRED constantly and cause an endless loop.

    Thx.

    --
    Regards/Gruss,
    Boris.

    https://people.kernel.org/tglx/notes-about-netiquette

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