linux-kernel - Re: [PATCH 0/3] Resolve problems with kexec identity mapping

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Message-ID: <Zo1SRIZEhveMwSPX@swahl-home.5wahls.com>
Date: Tue, 9 Jul 2024 10:07:48 -0500
From: Steve Wahl <steve.wahl@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: Ard Biesheuvel <ardb@...nel.org>, Steve Wahl <steve.wahl@....com>,
        Ashish Kalra <ashish.kalra@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org, Pavin Joseph <me@...injoseph.com>,
        Eric Hagberg <ehagberg@...il.com>, Simon Horman <horms@...ge.net.au>,
        Eric Biederman <ebiederm@...ssion.com>, Dave Young <dyoung@...hat.com>,
        Sarah Brofeldt <srhb@....dk>, Russ Anderson <rja@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Hou Wenlong <houwenlong.hwl@...group.com>,
        Andrew Morton <akpm@...ux-foundation.org>, Baoquan He <bhe@...hat.com>,
        Yuntao Wang <ytcoode@...il.com>, Bjorn Helgaas <bhelgaas@...gle.com>,
        Joerg Roedel <jroedel@...e.de>, Michael Roth <michael.roth@....com>
Subject: Re: [PATCH 0/3] Resolve problems with kexec identity mapping

On Tue, Jul 09, 2024 at 12:37:42PM +0200, Borislav Petkov wrote:
> On Tue, Jul 09, 2024 at 08:49:43AM +0200, Ard Biesheuvel wrote:
> > > Patch #2 adds the CC blob to the identity map as well, if present,
> > > since if present it is also dereferenced before the page fault handler
> > > can be put into place.  Given what's been discussed, this patch might
> > > not be necessary; I don't know enough to say whether kexec-ing a new
> > > kernel within a SEV guest makes sense.  I'm pretty certain it can
> > > cause no harm, though.
> 
> No, keep it in the bag until it is really needed. No proactive "fixing".
> 
> > I'd prefer it if that is addressed within the context of the SEV guest
> > work. The memory setup is quite intricate, and dealing with individual
> > types of EFI config tables is something we should avoid in general. I
> > still maintain that the best approach would be to map all of DRAM 1:1
> > instead of mapping patches left and right (as this is what EFI does),
> > but if we need to do so, let's keep it as generic as we possibly can.
> 
> Sure. There's the kink that coco guests need to accept memory first and
> mapping it all is the least performant one. But we can deal with that later.
> 
> > I wasn't cc'ed on any of the patches so I don't know exactly what was
> > discussed.
> > 
> > Please cc me and linux-efi@ on your next revision.
> 
> And please update your commit messages with what was discussed on this thread.
> 
> Thx.

Thanks, Boris.  I'll give it my best shot.

Next version will leave out the current patch #2, and update the
comments to include this conversation somehow summarized.

I think perhaps the cover letter was also too verbose on the history
and unintentionally hid the information necesary to understand the
situation.  I will try to make it more concise.

--> Steve


-- 
Steve Wahl, Hewlett Packard Enterprise