// SPDX-License-Identifier: GPL-2.0
#include <linux/errno.h>
#include <linux/gfp.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/memremap.h>
#include <linux/slab.h>

#include <asm/page.h>

#include <xen/balloon.h>
#include <xen/page.h>
#include <xen/xen.h>

static DEFINE_MUTEX(list_lock);
static struct page *page_list;
static unsigned int list_count;

static struct resource *target_resource;

/* Pages to subtract from the memory count when setting balloon target. */
unsigned long xen_unpopulated_pages __initdata;

/*
 * If arch is not happy with system "iomem_resource" being used for
 * the region allocation it can provide it's own view by creating specific
 * Xen resource with unused regions of guest physical address space provided
 * by the hypervisor.
 */
int __weak __init arch_xen_unpopulated_init(struct resource **res)
{
        *res = &iomem_resource;

        return 0;
}

static int fill_list(unsigned int nr_pages)
{
        struct dev_pagemap *pgmap;
        struct resource *res, *tmp_res = NULL;
        void *vaddr;
        unsigned int i, alloc_pages = round_up(nr_pages, PAGES_PER_SECTION);
        struct range mhp_range;
        int ret;

        res = kzalloc_obj(*res);
        if (!res)
                return -ENOMEM;

        res->name = "Xen scratch";
        res->flags = IORESOURCE_MEM | IORESOURCE_BUSY;

        mhp_range = mhp_get_pluggable_range(true);

        ret = allocate_resource(target_resource, res,
                                alloc_pages * PAGE_SIZE, mhp_range.start, mhp_range.end,
                                PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
        if (ret < 0) {
                pr_err("Cannot allocate new IOMEM resource\n");
                goto err_resource;
        }

        /*
         * Reserve the region previously allocated from Xen resource to avoid
         * re-using it by someone else.
         */
        if (target_resource != &iomem_resource) {
                tmp_res = kzalloc_obj(*tmp_res);
                if (!tmp_res) {
                        ret = -ENOMEM;
                        goto err_insert;
                }

                tmp_res->name = res->name;
                tmp_res->start = res->start;
                tmp_res->end = res->end;
                tmp_res->flags = res->flags;

                ret = request_resource(&iomem_resource, tmp_res);
                if (ret < 0) {
                        pr_err("Cannot request resource %pR (%d)\n", tmp_res, ret);
                        kfree(tmp_res);
                        goto err_insert;
                }
        }

        pgmap = kzalloc_obj(*pgmap);
        if (!pgmap) {
                ret = -ENOMEM;
                goto err_pgmap;
        }

        pgmap->type = MEMORY_DEVICE_GENERIC;
        pgmap->range = (struct range) {
                .start = res->start,
                .end = res->end,
        };
        pgmap->nr_range = 1;
        pgmap->owner = res;

#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_pv_domain()) {
                xen_pfn_t pfn = PFN_DOWN(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");
                                ret = -ENOMEM;
                                goto err_memremap;
                        }
                }
        }
#endif

        vaddr = memremap_pages(pgmap, NUMA_NO_NODE);
        if (IS_ERR(vaddr)) {
                pr_err("Cannot remap memory range\n");
                ret = PTR_ERR(vaddr);
                goto err_memremap;
        }

        for (i = 0; i < alloc_pages; i++) {
                struct page *pg = virt_to_page(vaddr + PAGE_SIZE * i);

                pg->zone_device_data = page_list;
                page_list = pg;
                list_count++;
        }

        return 0;

err_memremap:
        kfree(pgmap);
err_pgmap:
        if (tmp_res) {
                release_resource(tmp_res);
                kfree(tmp_res);
        }
err_insert:
        release_resource(res);
err_resource:
        kfree(res);
        return ret;
}

/**
 * xen_alloc_unpopulated_pages - alloc unpopulated pages
 * @nr_pages: Number of pages
 * @pages: pages returned
 * @return 0 on success, error otherwise
 */
int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages)
{
        unsigned int i;
        int ret = 0;

        /*
         * Fallback to default behavior if we do not have any suitable resource
         * to allocate required region from and as the result we won't be able to
         * construct pages.
         */
        if (!target_resource)
                return xen_alloc_ballooned_pages(nr_pages, pages);

        mutex_lock(&list_lock);
        if (list_count < nr_pages) {
                ret = fill_list(nr_pages - list_count);
                if (ret)
                        goto out;
        }

        for (i = 0; i < nr_pages; i++) {
                struct page *pg = page_list;

                BUG_ON(!pg);
                page_list = pg->zone_device_data;
                list_count--;
                pages[i] = pg;

#ifdef CONFIG_XEN_HAVE_PVMMU
                if (xen_pv_domain()) {
                        ret = xen_alloc_p2m_entry(page_to_pfn(pg));
                        if (ret < 0) {
                                unsigned int j;

                                for (j = 0; j <= i; j++) {
                                        pages[j]->zone_device_data = page_list;
                                        page_list = pages[j];
                                        list_count++;
                                }
                                goto out;
                        }
                }
#endif
        }

out:
        mutex_unlock(&list_lock);
        return ret;
}
EXPORT_SYMBOL(xen_alloc_unpopulated_pages);

/**
 * xen_free_unpopulated_pages - return unpopulated pages
 * @nr_pages: Number of pages
 * @pages: pages to return
 */
void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages)
{
        unsigned int i;

        if (!target_resource) {
                xen_free_ballooned_pages(nr_pages, pages);
                return;
        }

        mutex_lock(&list_lock);
        for (i = 0; i < nr_pages; i++) {
                pages[i]->zone_device_data = page_list;
                page_list = pages[i];
                list_count++;
        }
        mutex_unlock(&list_lock);
}
EXPORT_SYMBOL(xen_free_unpopulated_pages);

static int __init unpopulated_init(void)
{
        int ret;

        if (!xen_domain())
                return -ENODEV;

        ret = arch_xen_unpopulated_init(&target_resource);
        if (ret) {
                pr_err("xen:unpopulated: Cannot initialize target resource\n");
                target_resource = NULL;
        }

        return ret;
}
early_initcall(unpopulated_init);