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From:   Roland Dreier <roland@purestorage.com>
Date:   Fri, 24 Aug 2018 13:04:09 -0700
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Subject: Re: [PATCH 4.4 103/105] Revert "x86/mm/pat: Ensure cpa->pfn only
 contains page frame numbers"
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux@roeck-us.net, Ben Hutchings <ben.hutchings@codethink.co.uk>,
        LKML <linux-kernel@vger.kernel.org>, stable@vger.kernel.org,
        matt@codeblueprint.co.uk, bp@suse.de,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>, luto@kernel.org,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>, bp@alien8.de,
        brgerst@gmail.com, davej@codemonkey.org.uk, dvlasenk@redhat.com,
        "H. Peter Anvin" <hpa@zytor.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        sai.praneeth.prakhya@intel.com, sds@tycho.nsa.gov,
        Thomas Gleixner <tglx@linutronix.de>, toshi.kani@hp.com,
        linux-efi@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Yazen.Ghannam@amd.com
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> Ok, so what patch should be reverted?  I'm seeing other reports of
> problems all around this same area, but I can't figure out exactly what
> to do.

Are any of those reports public?  If so can you point me at them, I'm
curious if the symptoms match up.

I don't think we want to revert anything.  I think you should pull in
edc3b9129cec and at least the first three patches that Ben listed:

21cdb6b56843 x86/mm: Page align the '_end' symbol to avoid pfn conversion bugs
b61a76f8850d x86/efi: Map RAM into the identity page table for mixed mode
753b11ef8e92 x86/efi: Setup separate EFI page tables in kexec paths

the first patch takes a bit of massaging (mostly because some of it is
already touched by 02ff2769edbc, which keeps the changes from
edc3b9129cec, and so we can drop a good bit when applying).  The other
three apply cleanly.

I'm currently testing that and can send you the state of my tree in a bit.

 - R.