linux-kernel - Re: [RFC PATCH 4/5] EXPERIMENTAL: x86: use __GFP_UNMAPPED for modele

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Date:   Thu, 9 Mar 2023 01:54:30 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "rppt@...nel.org" <rppt@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "song@...nel.org" <song@...nel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "x86@...nel.org" <x86@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 4/5] EXPERIMENTAL: x86: use __GFP_UNMAPPED for
 modele_alloc()

On Wed, 2023-03-08 at 11:41 +0200, Mike Rapoport wrote:
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index ef910bf349e1..84220ec45ec2 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2892,7 +2892,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>          * to fails, fallback to a single page allocator that is
>          * more permissive.
>          */
> -       if (!order) {
> +       if (!order && !(gfp & __GFP_UNMAPPED)) {
>                 gfp_t bulk_gfp = gfp & ~__GFP_NOFAIL;
>  
>                 while (nr_allocated < nr_pages) {

This is obviously a quick POC patch, but I guess we should skip the
whole vm_remove_mappings() thing since it would reset the direct map to
RW for these unmapped pages. Or rather modules shouldn't set
VM_FLUSH_RESET_PERMS if it uses this.