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Commit 488f046d authored by Konrad Rzeszutek Wilk's avatar Konrad Rzeszutek Wilk
Browse files

xen/mmu: Recycle the Xen provided L4, L3, and L2 pages 



As we are not using them. We end up only using the L1 pagetables
and grafting those to our page-tables.

[v1: Per Stefano's suggestion squashed two commits]
[v2: Per Stefano's suggestion simplified loop]
[v3: Fix smatch warnings]
[v4: Add more comments]
Acked-by: default avatarStefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent caaf9ecf

arch/x86/xen/mmu.c

+35 −7
Original line number Diff line number Diff line
@@ -1708,7 +1708,20 @@ static void convert_pfn_mfn(void *v) 
	for (i = 0; i < PTRS_PER_PTE; i++)

		pte[i] = xen_make_pte(pte[i].pte);

}



static void __init check_pt_base(unsigned long *pt_base, unsigned long *pt_end,

				 unsigned long addr)

{

	if (*pt_base == PFN_DOWN(__pa(addr))) {

		set_page_prot((void *)addr, PAGE_KERNEL);

		clear_page((void *)addr);

		(*pt_base)++;

	}

	if (*pt_end == PFN_DOWN(__pa(addr))) {

		set_page_prot((void *)addr, PAGE_KERNEL);

		clear_page((void *)addr);

		(*pt_end)--;

	}

}

/*

 * Set up the initial kernel pagetable.

 *
@@ -1724,6 +1737,9 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn) 
{

	pud_t *l3;

	pmd_t *l2;

	unsigned long addr[3];

	unsigned long pt_base, pt_end;

	unsigned i;



	/* max_pfn_mapped is the last pfn mapped in the initial memory

	 * mappings. Considering that on Xen after the kernel mappings we
@@ -1731,6 +1747,9 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn) 
	 * set max_pfn_mapped to the last real pfn mapped. */

	max_pfn_mapped = PFN_DOWN(__pa(xen_start_info->mfn_list));



	pt_base = PFN_DOWN(__pa(xen_start_info->pt_base));

	pt_end = pt_base + xen_start_info->nr_pt_frames;



	/* Zap identity mapping */

	init_level4_pgt[0] = __pgd(0);
@@ -1749,6 +1768,9 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn) 
	l3 = m2v(pgd[pgd_index(__START_KERNEL_map)].pgd);

	l2 = m2v(l3[pud_index(__START_KERNEL_map)].pud);



	addr[0] = (unsigned long)pgd;

	addr[1] = (unsigned long)l3;

	addr[2] = (unsigned long)l2;

	/* Graft it onto L4[272][0]. Note that we creating an aliasing problem:

	 * Both L4[272][0] and L4[511][511] have entries that point to the same

	 * L2 (PMD) tables. Meaning that if you modify it in __va space
@@ -1782,20 +1804,26 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn) 
	/* Unpin Xen-provided one */

	pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd)));



	/* Switch over */

	pgd = init_level4_pgt;



	/*

	 * At this stage there can be no user pgd, and no page

	 * structure to attach it to, so make sure we just set kernel

	 * pgd.

	 */

	xen_mc_batch();

	__xen_write_cr3(true, __pa(pgd));

	__xen_write_cr3(true, __pa(init_level4_pgt));

	xen_mc_issue(PARAVIRT_LAZY_CPU);



	memblock_reserve(__pa(xen_start_info->pt_base),

			 xen_start_info->nr_pt_frames * PAGE_SIZE);

	/* We can't that easily rip out L3 and L2, as the Xen pagetables are

	 * set out this way: [L4], [L1], [L2], [L3], [L1], [L1] ...  for

	 * the initial domain. For guests using the toolstack, they are in:

	 * [L4], [L3], [L2], [L1], [L1], order .. So for dom0 we can only

	 * rip out the [L4] (pgd), but for guests we shave off three pages.

	 */

	for (i = 0; i < ARRAY_SIZE(addr); i++)

		check_pt_base(&pt_base, &pt_end, addr[i]);



	/* Our (by three pages) smaller Xen pagetable that we are using */

	memblock_reserve(PFN_PHYS(pt_base), (pt_end - pt_base) * PAGE_SIZE);

}

#else	/* !CONFIG_X86_64 */

static RESERVE_BRK_ARRAY(pmd_t, initial_kernel_pmd, PTRS_PER_PMD);