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

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Date:   Thu, 6 May 2021 11:24:18 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Linux MM <linux-mm@...ck.org>, x86@...nel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-hardening@...r.kernel.org,
        kernel-hardening@...ts.openwall.com,
        Ira Weiny <ira.weiny@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 5/9] x86, mm: Use cache of page tables

On Tue, May 4, 2021 at 5:36 PM Rick Edgecombe
<rick.p.edgecombe@...el.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.