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    SubjectRe: [RFC PATCH v3 20/20] x86: Add support to make use of Secure Memory Encryption
    On Tue, Nov 29, 2016 at 12:48:17PM -0600, Tom Lendacky wrote:
    > > One more thing: just like we're adding an =on switch, we'd need an =off
    > > switch in case something's wrong with the SME code. IOW, if a user
    > > supplies "mem_encrypt=off", we do not encrypt.
    >
    > Well, we can document "off", but if the exact string "mem_encrypt=on"
    > isn't specified on the command line then the encryption won't occur.

    So you have this:

    + /*
    + * Fixups have not been to applied phys_base yet, so we must obtain
    + * the address to the SME command line option in the following way.
    + */
    + asm ("lea sme_cmdline_arg(%%rip), %0"
    + : "=r" (cmdline_arg)
    + : "p" (sme_cmdline_arg));
    + cmdline_ptr = bp->hdr.cmd_line_ptr | ((u64)bp->ext_cmd_line_ptr << 32);
    + if (cmdline_find_option_bool((char *)cmdline_ptr, cmdline_arg))
    + sme_me_mask = 1UL << (ebx & 0x3f);

    If I parse this right, we will enable SME *only* if mem_encrypt=on is
    explicitly supplied on the command line.

    Which means, users will have to *know* about that cmdline switch first.
    Which then means, we have to go and tell them. Do you see where I'm
    going with this?

    I know we talked about this already but I still think we should enable
    it by default and people who don't want it will use the =off switch. We
    can also do something like CONFIG_AMD_SME_ENABLED_BY_DEFAULT which we
    can be selected during build for the different setups.

    Hmmm.

    --
    Regards/Gruss,
    Boris.

    Good mailing practices for 400: avoid top-posting and trim the reply.

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