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

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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: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
This commit is contained in:
Konrad Rzeszutek Wilk 2012-07-26 12:00:56 -04:00
parent caaf9ecf16
commit 488f046df9
1 changed files with 35 additions and 7 deletions
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42
arch/x86/xen/mmu.c
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@ -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);