linux-kernel - Re: [PATCH] Revert "x86/mm: implement free pmd/pte page interfaces"

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Date:   Fri, 27 Apr 2018 08:28:27 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     "Kani, Toshi" <toshi.kani@....com>
Cc:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "joro@...tes.org" <joro@...tes.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bp@...e.de" <bp@...e.de>,
        "willy@...radead.org" <willy@...radead.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "hpa@...or.com" <hpa@...or.com>, "Hocko, Michal" <MHocko@...e.com>,
        "jroedel@...e.de" <jroedel@...e.de>
Subject: Re: [PATCH] Revert "x86/mm: implement free pmd/pte page interfaces"


* Kani, Toshi <toshi.kani@....com> wrote:

> On Thu, 2018-04-26 at 17:14 +0200, Joerg Roedel wrote:
> > From: Joerg Roedel <jroedel@...e.de>
> > 
> > This reverts commit 28ee90fe6048fa7b7ceaeb8831c0e4e454a4cf89.
> > 
> > This commit is broken for x86, as it unmaps the PTE and PMD
> > pages and immediatly frees them without doing a TLB flush.
> > 
> > Further this lacks synchronization with other page-tables in
> > the system when the PMD pages are not shared between
> > mm_structs.
> > 
> > On x86-32 with PAE and PTI patches on-top this patch
> > triggers the BUG_ON in vmalloc_sync_one() because the kernel
> > and the process page-table were not synchronized.
> > 
> > Signed-off-by: Joerg Roedel <jroedel@...e.de>
> 
> I do not agree with the comments and this revert.  Let's discuss further
> on the original thread.

The original patch is totally broken (it's based on a misunderstanding), so unless 
you have a fix the revert is justified.

Thanks,

	Ingo