linux-kernel - Re: [PATCH 1/2] x86/tdx: Extract GET_INFO call from get_cc

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Date:   Mon, 31 Oct 2022 07:12:52 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        luto@...nel.org, peterz@...radead.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, ak@...ux.intel.com,
        dan.j.williams@...el.com, david@...hat.com, hpa@...or.com,
        seanjc@...gle.com, thomas.lendacky@....com,
        elena.reshetova@...el.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86/tdx: Extract GET_INFO call from get_cc_mask()

On Sat, Oct 29, 2022 at 02:59:51AM +0300, Kirill A. Shutemov wrote:
> > Can you please take a look through this and make sure I didn't botch
> > anything:
> > 
> > > https://git.kernel.org/pub/scm/linux/kernel/git/daveh/devel.git/log/?h=tdxbadve
> > 
> > The end result is about 50 lines less than what was there before.  Most
> > of it is comment removal but the code is simpler too.
> > 
> > Acks and Tested-by's would be appreciated.

One thing that I must bring up is that it seems that there's no way to get
the panic message to user. I tried to convinced myself that it is qemu
misconfiguration on my part or some race, but no: it is just too early for
earlyprintk.

We only get earlyprintk working after parse_early_options() which happens
well after tdx_early_init().

Moving panic() after earlyprintk working is not good idea as it exposes
kernel more: by the time we already have full #VE handler.

We can move it earlier into decompresser which has different earlyprintk
implementation. Not sure if it worth this. What do you think?

"tdx: Guest detected" printed from the same tdx_early_init() is visible if
boot goes far enough to initialize console (early or not) as printk adds
the message to the buffer, but no so luck for panic().

-- 
  Kiryl Shutsemau / Kirill A. Shutemov