linux-kernel - Re: [PATCH v5 3/3] xen: add helpers to allocate unpopulated memory

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Date:   Tue, 1 Sep 2020 16:45:39 +0200
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     <linux-kernel@...r.kernel.org>
CC:     Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        "Stefano Stabellini" <sstabellini@...nel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>, Wei Liu <wl@....org>,
        Yan Yankovskyi <yyankovskyi@...il.com>,
        <dri-devel@...ts.freedesktop.org>,
        <xen-devel@...ts.xenproject.org>, <linux-mm@...ck.org>,
        David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v5 3/3] xen: add helpers to allocate unpopulated memory

On Tue, Sep 01, 2020 at 10:33:26AM +0200, Roger Pau Monne wrote:
> +static int fill_list(unsigned int nr_pages)
> +{
> +	struct dev_pagemap *pgmap;
> +	void *vaddr;
> +	unsigned int i, alloc_pages = round_up(nr_pages, PAGES_PER_SECTION);
> +	int nid, ret;
> +
> +	pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL);
> +	if (!pgmap)
> +		return -ENOMEM;
> +
> +	pgmap->type = MEMORY_DEVICE_GENERIC;
> +	pgmap->res.name = "Xen scratch";
> +	pgmap->res.flags = IORESOURCE_MEM | IORESOURCE_BUSY;
> +
> +	ret = allocate_resource(&iomem_resource, &pgmap->res,
> +				alloc_pages * PAGE_SIZE, 0, -1,
> +				PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
> +	if (ret < 0) {
> +		pr_err("Cannot allocate new IOMEM resource\n");
> +		kfree(pgmap);
> +		return ret;
> +	}
> +
> +	nid = memory_add_physaddr_to_nid(pgmap->res.start);

I think this is not needed ...

> +
> +#ifdef CONFIG_XEN_HAVE_PVMMU
> +        /*
> +         * memremap will build page tables for the new memory so
> +         * the p2m must contain invalid entries so the correct
> +         * non-present PTEs will be written.
> +         *
> +         * If a failure occurs, the original (identity) p2m entries
> +         * are not restored since this region is now known not to
> +         * conflict with any devices.
> +         */
> +	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> +		xen_pfn_t pfn = PFN_DOWN(pgmap->res.start);
> +
> +		for (i = 0; i < alloc_pages; i++) {
> +			if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
> +				pr_warn("set_phys_to_machine() failed, no memory added\n");
> +				release_resource(&pgmap->res);
> +				kfree(pgmap);
> +				return -ENOMEM;
> +			}
> +                }
> +	}
> +#endif
> +
> +	vaddr = memremap_pages(pgmap, nid);

... and NUMA_NO_NODE should be used here instead, as this memory is just
fictitious space to map foreign memory, and shouldn't be related to
any NUMA node.

The following chunk should be folded in, or I can resend.

Thanks, Roger.
---8<---
diff --git a/drivers/xen/unpopulated-alloc.c b/drivers/xen/unpopulated-alloc.c
index 1b5d157c6977..3b98dc921426 100644
--- a/drivers/xen/unpopulated-alloc.c
+++ b/drivers/xen/unpopulated-alloc.c
@@ -20,7 +20,7 @@ static int fill_list(unsigned int nr_pages)
 	struct dev_pagemap *pgmap;
 	void *vaddr;
 	unsigned int i, alloc_pages = round_up(nr_pages, PAGES_PER_SECTION);
-	int nid, ret;
+	int ret;
 
 	pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL);
 	if (!pgmap)
@@ -39,8 +39,6 @@ static int fill_list(unsigned int nr_pages)
 		return ret;
 	}
 
-	nid = memory_add_physaddr_to_nid(pgmap->res.start);
-
 #ifdef CONFIG_XEN_HAVE_PVMMU
         /*
          * memremap will build page tables for the new memory so
@@ -65,7 +63,7 @@ static int fill_list(unsigned int nr_pages)
 	}
 #endif
 
-	vaddr = memremap_pages(pgmap, nid);
+	vaddr = memremap_pages(pgmap, NUMA_NO_NODE);
 	if (IS_ERR(vaddr)) {
 		pr_err("Cannot remap memory range\n");
 		release_resource(&pgmap->res);