Re: [PATCH 2/3] x86/mm: Sync also unmappings in vmalloc_sync_one()

From: Thomas Gleixner <tglx@linutronix.de>
To: Joerg Roedel <jroedel@suse.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()
Date: Thu, 18 Jul 2019 11:04:57 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1907181103120.1984@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20190718084654.GF13091@suse.de>

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.

Thanks,

	tglx