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Date:   Sat, 27 Oct 2018 16:51:51 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     lijiang <lijiang@redhat.com>
Cc:     Baoquan He <bhe@redhat.com>, Petr Tesarik <ptesarik@suse.cz>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        kexec@lists.infradead.org, mingo@redhat.com, tglx@linutronix.de,
        dyoung@redhat.com
Subject: Re: [PATCH] kdump, vmcoreinfo: Export sme_me_mask value to vmcoreinfo
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On Sat, Oct 27, 2018 at 10:41:56PM +0800, lijiang wrote:
> Actually, the value of 'sme_me_mask' is 0x800000000000 when SME is
> enabled, otherwise it is 0. That is to say, if the bit 47 is set, the
> bit number is also 0x800000000000 (1 << 47UL);

Yes, and you can simply copy the mask into your variable and export
that. Thinking about it more, though, it might be better if you instead
export a smaller value - not an u64 - and construct the mask in
userspace. I.e., a u8 which should be enough for your current purposes.

I say current because if it turns out we need to export more SME-related
info to userspace, exporting an u64 and then OR-ing in more information
in it would allow that. u8 not so much. So doing something like:

[ misc	   ][ enc bit  ][ other misc SME info 				      ]
0000_0000_0000_0000_1000_0000_0000_0000_0000_0000_0000_0000_0000_0000_0000_0000
63   59   55   51   47   43   39   35   31   27   23   19   15   11   7    3

would allow for exporting that additional info.

Especially if we want to use VMCOREINFO for more than kexec things.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--