linux-kernel - Re: [PATCH] x86/purgatory: provide config to disable purgatory

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Message-ID: <YaTd4ZID7O+bVRXT@redhat.com>
Date:   Mon, 29 Nov 2021 09:04:17 -0500
From:   Vivek Goyal <vgoyal@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Usama Arif <usama.arif@...edance.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        fam.zheng@...edance.com,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Baoquan He <bhe@...hat.com>, Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH] x86/purgatory: provide config to disable purgatory

On Tue, Nov 23, 2021 at 04:24:01PM +0100, Borislav Petkov wrote:
> On Tue, Nov 23, 2021 at 03:05:08PM +0000, Usama Arif wrote:
> > This can help in reducing boot time if purgatory is not needed
> > as the sha256 digest of kexec segments is no longer calculated
> > or verified if the config is disabled.
> 
> I'd prefer a commit message to say:
> 
> "Disable purgatory because of real-life use case X. With it disabled,
> booting a second kernel is sped up by Y."
> 
> "Just because" and adding yet another config option is not worth the
> effort, otherwise.

Agreed. What's the use case.

Also this cheksum is used to make sure purgatory is not corrupted. So
this is sort of saftey mechanism to make sure things are still the
same as we expected before we start executing this piece of code. Hence
this does not sound like an optional feature to me (even if it speeds
up things a bit).

BTW, how much speed up do you see.

Thanks
Vivek