linux-kernel - Re: [PATCH 4.4 103/105] Revert "x86/mm/pat: Ensure cpa->pfn only contains page frame numbers"

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Date:   Fri, 24 Aug 2018 15:54:31 +0100
From:   Matt Fleming <matt@...eblueprint.co.uk>
To:     Roland Dreier <roland@...estorage.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        ben.hutchings@...ethink.co.uk, LKML <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org, bp@...e.de,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>, luto@...nel.org,
        ard.biesheuvel@...aro.org, bp@...en8.de, brgerst@...il.com,
        davej@...emonkey.org.uk, dvlasenk@...hat.com,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        sai.praneeth.prakhya@...el.com, sds@...ho.nsa.gov,
        Thomas Gleixner <tglx@...utronix.de>, toshi.kani@...com,
        linux-efi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Yazen.Ghannam@....com
Subject: Re: [PATCH 4.4 103/105] Revert "x86/mm/pat: Ensure cpa->pfn only
 contains page frame numbers"

On Thu, 23 Aug, at 09:37:28AM, Roland Dreier wrote:
> > > This is bad enough that 4.4.148 and all newer 4.4.y crash early in
> > > boot on some EFI systems that I have.
> >
> > Ugh, not good.
> >
> > > For now I am re-applying the "ensure cpa->pfn only contains page frame
> > > numbers" patch, ported on top of 4.4.151.
> >
> > I can try to add it back and see what blows up, want me to attempt that?
> 
> Not sure what to say... the current state is obviously broken.  If you
> look at what 02ff2769edbc is doing, it's clear that we're now shifting
> cpa->pfn by PAGE_SHIFT where we weren't before, so we're putting bogus
> values in the page table.  And this is enough that my server system
> booting with EFI crashes early in boot efi_enter_virtual_mode() with
> the symptom that NX is improperly set on some pages (booting with
> "noexec=off" fixes things, although obviously I don't want to run that
> way).  FWIW I can confirm that reverting the single patch 02ff2769edbc
> fixes things, as does the cpa->pfn fix I mentioned above.
> 
> It's hard for me to make a call on applying "ensure cpa->pfn only
> contains page frame numbers" without knowing the problems it caused
> before.  The patch looks fine to me and I definitely need it, but
> maybe it exposes some other bug elsewhere?  Maybe Ben or Matt remember
> more above why this was reverted in 4.4.106?  Otherwise I'd say yeah,
> we should re-apply it, since I don't think we want to revert
> 02ff2769edbc.

For the record, I wasn't even aware it had been reverted.