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Date:   Fri, 19 Jul 2019 16:01:22 +0200
From:   Joerg Roedel <jroedel@suse.de>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Joerg Roedel <joro@8bytes.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 2/3] x86/mm: Sync also unmappings in vmalloc_sync_one()
Message-ID: <20190719140122.GF19068@suse.de>
References: <20190717071439.14261-1-joro@8bytes.org>
 <20190717071439.14261-3-joro@8bytes.org>
 <alpine.DEB.2.21.1907172337590.1778@nanos.tec.linutronix.de>
 <20190718084654.GF13091@suse.de>
 <alpine.DEB.2.21.1907181103120.1984@nanos.tec.linutronix.de>
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On Thu, Jul 18, 2019 at 11:04:57AM +0200, Thomas Gleixner wrote:
> Joerg,
> 
> On Thu, 18 Jul 2019, Joerg Roedel wrote:
> > On Wed, Jul 17, 2019 at 11:43:43PM +0200, Thomas Gleixner wrote:
> > > On Wed, 17 Jul 2019, Joerg Roedel wrote:
> > > > +
> > > > +	if (!pmd_present(*pmd_k))
> > > > +		return NULL;
> > > >  	else
> > > >  		BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));
> > > 
> > > So in case of unmap, this updates only the first entry in the pgd_list
> > > because vmalloc_sync_all() will break out of the iteration over pgd_list
> > > when NULL is returned from vmalloc_sync_one().
> > > 
> > > I'm surely missing something, but how is that supposed to sync _all_ page
> > > tables on unmap as the changelog claims?
> > 
> > No, you are right, I missed that. It is a bug in this patch, the code
> > that breaks out of the loop in vmalloc_sync_all() needs to be removed as
> > well. Will do that in the next version.
> 
> I assume that p4d/pud do not need the pmd treatment, but a comment
> explaining why would be appreciated.

Actually there is already a comment in this function explaining why p4d
and pud don't need any treatment:

        /*
         * set_pgd(pgd, *pgd_k); here would be useless on PAE
         * and redundant with the set_pmd() on non-PAE. As would
         * set_p4d/set_pud.
         */ 

I couldn't say it with less words :)


Regards,

	Joerg