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Commit 2bad07ce authored by David Vrabel's avatar David Vrabel Committed by Stefano Stabellini
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xen/balloon: ensure preemption is disabled when using a scratch page 



In decrease_reservation(), if the kernel is preempted between updating
the mapping and updating the p2m then they may end up using different
scratch pages.

Use get_balloon_scratch_page() and put_balloon_scratch_page() which use
get_cpu_var() and put_cpu_var() to correctly disable preemption.

Signed-off-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
Signed-off-by: default avatarStefano Stabellini <stefano.stabellini@eu.citrix.com>
Tested-by: default avatarSander Eikelenboom <linux@eikelenboom.it>
parent c3b7cb1f

drivers/xen/balloon.c

+7 −4
Original line number Diff line number Diff line
@@ -380,6 +380,7 @@ 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;

	struct page   *scratch_page;

	int ret;

	struct xen_memory_reservation reservation = {

		.address_bits = 0,
@@ -399,6 +400,8 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) 
	if (nr_pages > ARRAY_SIZE(frame_list))

		nr_pages = ARRAY_SIZE(frame_list);



	scratch_page = get_balloon_scratch_page();



	for (i = 0; i < nr_pages; i++) {

		page = alloc_page(gfp);

		if (page == NULL) {
@@ -416,7 +419,7 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) 
		if (xen_pv_domain() && !PageHighMem(page)) {

			ret = HYPERVISOR_update_va_mapping(

				(unsigned long)__va(pfn << PAGE_SHIFT),

				pfn_pte(page_to_pfn(__get_cpu_var(balloon_scratch_page)),

				pfn_pte(page_to_pfn(scratch_page),

					PAGE_KERNEL_RO), 0);

			BUG_ON(ret);

		}
@@ -432,14 +435,14 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) 
		pfn = mfn_to_pfn(frame_list[i]);

		if (!xen_feature(XENFEAT_auto_translated_physmap)) {

			unsigned long p;

			struct page *pg;

			pg = __get_cpu_var(balloon_scratch_page);

			p = page_to_pfn(pg);

			p = page_to_pfn(scratch_page);

			__set_phys_to_machine(pfn, pfn_to_mfn(p));

		}

		balloon_append(pfn_to_page(pfn));

	}



	put_balloon_scratch_page();



	set_xen_guest_handle(reservation.extent_start, frame_list);

	reservation.nr_extents   = nr_pages;

	ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);