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References: <20210505003032.489164-1-rick.p.edgecombe@intel.com> <20210505003032.489164-6-rick.p.edgecombe@intel.com>
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From:   Shakeel Butt <shakeelb@google.com>
Date:   Thu, 6 May 2021 11:24:18 -0700
Message-ID: <CALvZod7ieLEObX0y-7X+_zMwaVN5o0P-ZwZVLqCAK5ytQrNs9w@mail.gmail.com>
Subject: Re: [PATCH RFC 5/9] x86, mm: Use cache of page tables
To:     Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc:     Dave Hansen <dave.hansen@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Linux MM <linux-mm@kvack.org>, x86@kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-hardening@vger.kernel.org,
        kernel-hardening@lists.openwall.com,
        Ira Weiny <ira.weiny@intel.com>,
        Mike Rapoport <rppt@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        LKML <linux-kernel@vger.kernel.org>
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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.