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

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Message-ID: <1524858493.2693.535.camel@hpe.com>
Date:   Fri, 27 Apr 2018 19:49:04 +0000
From:   "Kani, Toshi" <toshi.kani@....com>
To:     "mingo@...nel.org" <mingo@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bp@...e.de" <bp@...e.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "willy@...radead.org" <willy@...radead.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "joro@...tes.org" <joro@...tes.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "Hocko, Michal" <MHocko@...e.com>,
        "jroedel@...e.de" <jroedel@...e.de>
Subject: Re: [PATCH] Revert "x86/mm: implement free pmd/pte page interfaces"

On Fri, 2018-04-27 at 08:28 +0200, Ingo Molnar wrote:
> * 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.

I am working on a fix on top of this patch.

Thanks,
-Toshi