Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH 6/6] x86/xen: open code alloc_vm_area in
 arch_gnttab_valloc
To:     Christoph Hellwig <hch@lst.de>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Minchan Kim <minchan@kernel.org>,
        Nitin Gupta <ngupta@vflare.org>, x86@kernel.org,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-mm@kvack.org
References: <20200918163724.2511-1-hch@lst.de>
 <20200918163724.2511-7-hch@lst.de>
From:   boris.ostrovsky@oracle.com
Organization: Oracle Corporation
Message-ID: <0833b9a8-5096-d105-a850-1336150eada1@oracle.com>
Date:   Mon, 21 Sep 2020 16:44:10 -0400
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0)
 Gecko/20100101 Thunderbird/78.2.1
MIME-Version: 1.0
In-Reply-To: <20200918163724.2511-7-hch@lst.de>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Precedence: bulk


On 9/18/20 12:37 PM, Christoph Hellwig wrote:
>  
> +static int gnttab_apply(pte_t *pte, unsigned long addr, void *data)
> +{
> +	pte_t ***p = data;
> +
> +	**p = pte;
> +	(*p)++;
> +	return 0;
> +}
> +
>  static int arch_gnttab_valloc(struct gnttab_vm_area *area, unsigned nr_frames)
>  {
>  	area->ptes = kmalloc_array(nr_frames, sizeof(*area->ptes), GFP_KERNEL);
>  	if (area->ptes == NULL)
>  		return -ENOMEM;
> -
> -	area->area = alloc_vm_area(PAGE_SIZE * nr_frames, area->ptes);
> -	if (area->area == NULL) {
> -		kfree(area->ptes);
> -		return -ENOMEM;
> -	}
> -
> +	area->area = get_vm_area(PAGE_SIZE * nr_frames, VM_IOREMAP);
> +	if (!area->area)
> +		goto out_free_ptes;
> +	if (apply_to_page_range(&init_mm, (unsigned long)area->area->addr,
> +			PAGE_SIZE * nr_frames, gnttab_apply, &area->ptes))


This will end up incrementing area->ptes pointer. So perhaps something like


pte_t **ptes = area->ptes;

if (apply_to_page_range(&init_mm, (unsigned long)area->area->addr,
                        PAGE_SIZE * nr_frames, gnttab_apply, &ptes)) {

       ...

}


-boris