balloon.c

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/******************************************************************************
 * Xen balloon driver - enables returning/claiming memory to/from Xen.
 *
 * Copyright (c) 2003, B Dragovic
 * Copyright (c) 2003-2004, M Williamson, K Fraser
 * Copyright (c) 2005 Dan M. Smith, IBM Corporation
 * Copyright (c) 2010 Daniel Kiper
 *
 * Memory hotplug support was written by Daniel Kiper. Work on
 * it was sponsored by Google under Google Summer of Code 2010
 * program. Jeremy Fitzhardinge from Citrix was the mentor for
 * this project.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version 2
 * as published by the Free Software Foundation; or, when distributed
 * separately from the Linux kernel or incorporated into other
 * software packages, subject to the following license:
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this source file (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/errno.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/bootmem.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/mutex.h>
#include <linux/list.h>
#include <linux/gfp.h>
#include <linux/notifier.h>
#include <linux/memory.h>
#include <linux/memory_hotplug.h>

#include <asm/page.h>
#include <asm/pgalloc.h>
#include <asm/pgtable.h>
#include <asm/tlb.h>

#include <asm/xen/hypervisor.h>
#include <asm/xen/hypercall.h>

#include <xen/xen.h>
#include <xen/interface/xen.h>
#include <xen/interface/memory.h>
#include <xen/balloon.h>
#include <xen/features.h>
#include <xen/page.h>

/*
 * balloon_process() state:
 *
 * BP_DONE: done or nothing to do,
 * BP_EAGAIN: error, go to sleep,
 * BP_ECANCELED: error, balloon operation canceled.
 */

enum bp_state {
    BP_DONE,
    BP_EAGAIN,
    BP_ECANCELED
};


static DEFINE_MUTEX(balloon_mutex);

struct balloon_stats balloon_stats;
EXPORT_SYMBOL_GPL(balloon_stats);

/* We increase/decrease in batches which fit in a page */
static xen_pfn_t frame_list[PAGE_SIZE / sizeof(unsigned long)];

#ifdef CONFIG_HIGHMEM
#define inc_totalhigh_pages() (totalhigh_pages++)
#define dec_totalhigh_pages() (totalhigh_pages--)
#else
#define inc_totalhigh_pages() do {} while (0)
#define dec_totalhigh_pages() do {} while (0)
#endif

/* List of ballooned pages, threaded through the mem_map array. */
static LIST_HEAD(ballooned_pages);

/* Main work function, always executed in process context. */
static void balloon_process(struct work_struct *work);
static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);

/* When ballooning out (allocating memory to return to Xen) we don't really
   want the kernel to try too hard since that can trigger the oom killer. */
#define GFP_BALLOON \
    (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)

static void scrub_page(struct page *page)
{
#ifdef CONFIG_XEN_SCRUB_PAGES
    clear_highpage(page);
#endif
}

/* balloon_append: add the given page to the balloon. */
static void __balloon_append(struct page *page)
{
    /* Lowmem is re-populated first, so highmem pages go at list tail. */
    if (PageHighMem(page)) {
        list_add_tail(&page->lru, &ballooned_pages);
        balloon_stats.balloon_high++;
    } else {
        list_add(&page->lru, &ballooned_pages);
        balloon_stats.balloon_low++;
    }
}

static void balloon_append(struct page *page)
{
    __balloon_append(page);
    if (PageHighMem(page))
        dec_totalhigh_pages();
    totalram_pages--;
}

/* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
static struct page *balloon_retrieve(bool prefer_highmem)
{
    struct page *page;

    if (list_empty(&ballooned_pages))
        return NULL;

    if (prefer_highmem)
        page = list_entry(ballooned_pages.prev, struct page, lru);
    else
        page = list_entry(ballooned_pages.next, struct page, lru);
    list_del(&page->lru);

    if (PageHighMem(page)) {
        balloon_stats.balloon_high--;
        inc_totalhigh_pages();
    } else
        balloon_stats.balloon_low--;

    totalram_pages++;

    return page;
}

static struct page *balloon_first_page(void)
{
    if (list_empty(&ballooned_pages))
        return NULL;
    return list_entry(ballooned_pages.next, struct page, lru);
}

static struct page *balloon_next_page(struct page *page)
{
    struct list_head *next = page->lru.next;
    if (next == &ballooned_pages)
        return NULL;
    return list_entry(next, struct page, lru);
}

static enum bp_state update_schedule(enum bp_state state)
{
    if (state == BP_DONE) {
        balloon_stats.schedule_delay = 1;
        balloon_stats.retry_count = 1;
        return BP_DONE;
    }

    ++balloon_stats.retry_count;

    if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&
            balloon_stats.retry_count > balloon_stats.max_retry_count) {
        balloon_stats.schedule_delay = 1;
        balloon_stats.retry_count = 1;
        return BP_ECANCELED;
    }

    balloon_stats.schedule_delay <<= 1;

    if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)
        balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;

    return BP_EAGAIN;
}

#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
static long current_credit(void)
{
    return balloon_stats.target_pages - balloon_stats.current_pages -
        balloon_stats.hotplug_pages;
}

static bool balloon_is_inflated(void)
{
    if (balloon_stats.balloon_low || balloon_stats.balloon_high ||
            balloon_stats.balloon_hotplug)
        return true;
    else
        return false;
}

/*
 * reserve_additional_memory() adds memory region of size >= credit above
 * max_pfn. New region is section aligned and size is modified to be multiple
 * of section size. Those features allow optimal use of address space and
 * establish proper alignment when this function is called first time after
 * boot (last section not fully populated at boot time contains unused memory
 * pages with PG_reserved bit not set; online_pages_range() does not allow page
 * onlining in whole range if first onlined page does not have PG_reserved
 * bit set). Real size of added memory is established at page onlining stage.
 */

static enum bp_state reserve_additional_memory(long credit)
{
    int nid, rc;
    u64 hotplug_start_paddr;
    unsigned long balloon_hotplug = credit;

    hotplug_start_paddr = PFN_PHYS(SECTION_ALIGN_UP(max_pfn));
    balloon_hotplug = round_up(balloon_hotplug, PAGES_PER_SECTION);
    nid = memory_add_physaddr_to_nid(hotplug_start_paddr);

    rc = add_memory(nid, hotplug_start_paddr, balloon_hotplug << PAGE_SHIFT);

    if (rc) {
        pr_info("xen_balloon: %s: add_memory() failed: %i\n", __func__, rc);
        return BP_EAGAIN;
    }

    balloon_hotplug -= credit;

    balloon_stats.hotplug_pages += credit;
    balloon_stats.balloon_hotplug = balloon_hotplug;

    return BP_DONE;
}

static void xen_online_page(struct page *page)
{
    __online_page_set_limits(page);

    mutex_lock(&balloon_mutex);

    __balloon_append(page);

    if (balloon_stats.hotplug_pages)
        --balloon_stats.hotplug_pages;
    else
        --balloon_stats.balloon_hotplug;

    mutex_unlock(&balloon_mutex);
}

static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
{
    if (val == MEM_ONLINE)
        schedule_delayed_work(&balloon_worker, 0);

    return NOTIFY_OK;
}

static struct notifier_block xen_memory_nb = {
    .notifier_call = xen_memory_notifier,
    .priority = 0
};
#else
static long current_credit(void)
{
    unsigned long target = balloon_stats.target_pages;

    target = min(target,
             balloon_stats.current_pages +
             balloon_stats.balloon_low +
             balloon_stats.balloon_high);

    return target - balloon_stats.current_pages;
}

static bool balloon_is_inflated(void)
{
    if (balloon_stats.balloon_low || balloon_stats.balloon_high)
        return true;
    else
        return false;
}

static enum bp_state reserve_additional_memory(long credit)
{
    balloon_stats.target_pages = balloon_stats.current_pages;
    return BP_DONE;
}
#endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */

static enum bp_state increase_reservation(unsigned long nr_pages)
{
    int rc;
    unsigned long  pfn, i;
    struct page   *page;
    struct xen_memory_reservation reservation = {
        .address_bits = 0,
        .extent_order = 0,
        .domid        = DOMID_SELF
    };

#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
    if (!balloon_stats.balloon_low && !balloon_stats.balloon_high) {
        nr_pages = min(nr_pages, balloon_stats.balloon_hotplug);
        balloon_stats.hotplug_pages += nr_pages;
        balloon_stats.balloon_hotplug -= nr_pages;
        return BP_DONE;
    }
#endif

    if (nr_pages > ARRAY_SIZE(frame_list))
        nr_pages = ARRAY_SIZE(frame_list);

    page = balloon_first_page();
    for (i = 0; i < nr_pages; i++) {
        if (!page) {
            nr_pages = i;
            break;
        }
        frame_list[i] = page_to_pfn(page);
        page = balloon_next_page(page);
    }

    set_xen_guest_handle(reservation.extent_start, frame_list);
    reservation.nr_extents = nr_pages;
    rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
    if (rc <= 0)
        return BP_EAGAIN;

    for (i = 0; i < rc; i++) {
        page = balloon_retrieve(false);
        BUG_ON(page == NULL);

        pfn = page_to_pfn(page);
        BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
               phys_to_machine_mapping_valid(pfn));

        set_phys_to_machine(pfn, frame_list[i]);

        /* Link back into the page tables if not highmem. */
        if (xen_pv_domain() && !PageHighMem(page)) {
            int ret;
            ret = HYPERVISOR_update_va_mapping(
                (unsigned long)__va(pfn << PAGE_SHIFT),
                mfn_pte(frame_list[i], PAGE_KERNEL),
                0);
            BUG_ON(ret);
        }

        /* Relinquish the page back to the allocator. */
        ClearPageReserved(page);
        init_page_count(page);
        __free_page(page);
    }

    balloon_stats.current_pages += rc;

    return BP_DONE;
}

static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
{
    enum bp_state state = BP_DONE;
    unsigned long  pfn, i;
    struct page   *page;
    int ret;
    struct xen_memory_reservation reservation = {
        .address_bits = 0,
        .extent_order = 0,
        .domid        = DOMID_SELF
    };

#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
    if (balloon_stats.hotplug_pages) {
        nr_pages = min(nr_pages, balloon_stats.hotplug_pages);
        balloon_stats.hotplug_pages -= nr_pages;
        balloon_stats.balloon_hotplug += nr_pages;
        return BP_DONE;
    }
#endif

    if (nr_pages > ARRAY_SIZE(frame_list))
        nr_pages = ARRAY_SIZE(frame_list);

    for (i = 0; i < nr_pages; i++) {
        if ((page = alloc_page(gfp)) == NULL) {
            nr_pages = i;
            state = BP_EAGAIN;
            break;
        }

        pfn = page_to_pfn(page);
        frame_list[i] = pfn_to_mfn(pfn);

        scrub_page(page);

        if (xen_pv_domain() && !PageHighMem(page)) {
            ret = HYPERVISOR_update_va_mapping(
                (unsigned long)__va(pfn << PAGE_SHIFT),
                __pte_ma(0), 0);
            BUG_ON(ret);
        }

    }

    /* Ensure that ballooned highmem pages don't have kmaps. */
    kmap_flush_unused();
    flush_tlb_all();

    /* No more mappings: invalidate P2M and add to balloon. */
    for (i = 0; i < nr_pages; i++) {
        pfn = mfn_to_pfn(frame_list[i]);
        __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
        balloon_append(pfn_to_page(pfn));
    }

    set_xen_guest_handle(reservation.extent_start, frame_list);
    reservation.nr_extents   = nr_pages;
    ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
    BUG_ON(ret != nr_pages);

    balloon_stats.current_pages -= nr_pages;

    return state;
}

/*
 * We avoid multiple worker processes conflicting via the balloon mutex.
 * We may of course race updates of the target counts (which are protected
 * by the balloon lock), or with changes to the Xen hard limit, but we will
 * recover from these in time.
 */
static void balloon_process(struct work_struct *work)
{
    enum bp_state state = BP_DONE;
    long credit;

    mutex_lock(&balloon_mutex);

    do {
        credit = current_credit();

        if (credit > 0) {
            if (balloon_is_inflated())
                state = increase_reservation(credit);
            else
                state = reserve_additional_memory(credit);
        }

        if (credit < 0)
            state = decrease_reservation(-credit, GFP_BALLOON);

        state = update_schedule(state);

#ifndef CONFIG_PREEMPT
        if (need_resched())
            schedule();
#endif
    } while (credit && state == BP_DONE);

    /* Schedule more work if there is some still to be done. */
    if (state == BP_EAGAIN)
        schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);

    mutex_unlock(&balloon_mutex);
}

/* Resets the Xen limit, sets new target, and kicks off processing. */
void balloon_set_new_target(unsigned long target)
{
    /* No need for lock. Not read-modify-write updates. */
    balloon_stats.target_pages = target;
    schedule_delayed_work(&balloon_worker, 0);
}
EXPORT_SYMBOL_GPL(balloon_set_new_target);

int alloc_xenballooned_pages(int nr_pages, struct page **pages, bool highmem)
{
    int pgno = 0;
    struct page *page;
    mutex_lock(&balloon_mutex);
    while (pgno < nr_pages) {
        page = balloon_retrieve(highmem);
        if (page && (highmem || !PageHighMem(page))) {
            pages[pgno++] = page;
        } else {
            enum bp_state st;
            if (page)
                balloon_append(page);
            st = decrease_reservation(nr_pages - pgno,
                    highmem ? GFP_HIGHUSER : GFP_USER);
            if (st != BP_DONE)
                goto out_undo;
        }
    }
    mutex_unlock(&balloon_mutex);
    return 0;
 out_undo:
    while (pgno)
        balloon_append(pages[--pgno]);
    /* Free the memory back to the kernel soon */
    schedule_delayed_work(&balloon_worker, 0);
    mutex_unlock(&balloon_mutex);
    return -ENOMEM;
}
EXPORT_SYMBOL(alloc_xenballooned_pages);

void free_xenballooned_pages(int nr_pages, struct page **pages)
{
    int i;

    mutex_lock(&balloon_mutex);

    for (i = 0; i < nr_pages; i++) {
        if (pages[i])
            balloon_append(pages[i]);
    }

    /* The balloon may be too large now. Shrink it if needed. */
    if (current_credit())
        schedule_delayed_work(&balloon_worker, 0);

    mutex_unlock(&balloon_mutex);
}
EXPORT_SYMBOL(free_xenballooned_pages);

static void __init balloon_add_region(unsigned long start_pfn,
                      unsigned long pages)
{
    unsigned long pfn, extra_pfn_end;
    struct page *page;

    /*
     * If the amount of usable memory has been limited (e.g., with
     * the 'mem' command line parameter), don't add pages beyond
     * this limit.
     */
    extra_pfn_end = min(max_pfn, start_pfn + pages);

    for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) {
        page = pfn_to_page(pfn);
        /* totalram_pages and totalhigh_pages do not
           include the boot-time balloon extension, so
           don't subtract from it. */
        __balloon_append(page);
    }
}

static int __init balloon_init(void)
{
    int i;

    if (!xen_domain())
        return -ENODEV;

    pr_info("xen/balloon: Initialising balloon driver.\n");

    balloon_stats.current_pages = xen_pv_domain()
        ? min(xen_start_info->nr_pages - xen_released_pages, max_pfn)
        : max_pfn;
    balloon_stats.target_pages  = balloon_stats.current_pages;
    balloon_stats.balloon_low   = 0;
    balloon_stats.balloon_high  = 0;

    balloon_stats.schedule_delay = 1;
    balloon_stats.max_schedule_delay = 32;
    balloon_stats.retry_count = 1;
    balloon_stats.max_retry_count = RETRY_UNLIMITED;

#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
    balloon_stats.hotplug_pages = 0;
    balloon_stats.balloon_hotplug = 0;

    set_online_page_callback(&xen_online_page);
    register_memory_notifier(&xen_memory_nb);
#endif

    /*
     * Initialize the balloon with pages from the extra memory
     * regions (see arch/x86/xen/setup.c).
     */
    for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++)
        if (xen_extra_mem[i].size)
            balloon_add_region(PFN_UP(xen_extra_mem[i].start),
                       PFN_DOWN(xen_extra_mem[i].size));

    return 0;
}

subsys_initcall(balloon_init);

MODULE_LICENSE("GPL");