Re: [PATCH RFC 5/9] x86, mm: Use cache of page tables

From: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
To: "shakeelb@google.com" <shakeelb@google.com>
Cc: "kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
	"luto@kernel.org" <luto@kernel.org>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"rppt@kernel.org" <rppt@kernel.org>,
	"linux-hardening@vger.kernel.org"
	<linux-hardening@vger.kernel.org>,
	"Weiny, Ira" <ira.weiny@intel.com>,
	"Williams, Dan J" <dan.j.williams@intel.com>
Subject: Re: [PATCH RFC 5/9] x86, mm: Use cache of page tables
Date: Fri, 7 May 2021 16:27:27 +0000	[thread overview]
Message-ID: <588d4b82a6cb47383e73e5d375b2b1766b4d3511.camel@intel.com> (raw)
In-Reply-To: <CALvZod7ieLEObX0y-7X+_zMwaVN5o0P-ZwZVLqCAK5ytQrNs9w@mail.gmail.com>

On Thu, 2021-05-06 at 11:24 -0700, Shakeel Butt wrote:
> On Tue, May 4, 2021 at 5:36 PM Rick Edgecombe
> <rick.p.edgecombe@intel.com> wrote:
> > 
> [...]
> > +#ifdef CONFIG_PKS_PG_TABLES
> > +struct page *alloc_table(gfp_t gfp)
> > +{
> > +       struct page *table;
> > +
> > +       if (!pks_page_en)
> > +               return alloc_page(gfp);
> > +
> > +       table = get_grouped_page(numa_node_id(), &gpc_pks);
> > +       if (!table)
> > +               return NULL;
> > +
> > +       if (gfp & __GFP_ZERO)
> > +               memset(page_address(table), 0, PAGE_SIZE);
> > +
> > +       if (memcg_kmem_enabled() &&
> > +           gfp & __GFP_ACCOUNT &&
> > +           !__memcg_kmem_charge_page(table, gfp, 0)) {
> > +               free_table(table);
> > +               table = NULL;
> > +       }
> > +
> > +       VM_BUG_ON_PAGE(*(unsigned long *)&table->ptl, table);
> 
> table can be NULL due to charge failure.

Argh, yes. Thank you. I'll remove the VM_BUG_ON, it was left
accidentally.