lkml.org 
[lkml]   [2012]   [Aug]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Xen-devel] [PATCH 07/11] xen/mmu: Recycle the Xen provided L4, L3, and L2 pages
On Thu, 16 Aug 2012, Konrad Rzeszutek Wilk wrote:
> 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]
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> ---
> arch/x86/xen/mmu.c | 40 +++++++++++++++++++++++++++++++++-------
> 1 files changed, 33 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index a59070b..bd92c82 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -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 = PFN_DOWN(__pa(xen_start_info->pt_base + (xen_start_info->nr_pt_frames * PAGE_SIZE)));

code style

> /* 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 +1804,24 @@ 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 .. */
> + for (i = 0; i < ARRAY_SIZE(addr); i++)
> + check_pt_base(&pt_base, &pt_end, addr[i]);

It is much clearer now, but if the comment is correct, doesn't it mean
that we are going to be able to free pgd, l3 and l2 only in the non-dom0
case?
If so it might be worth saying it explicitly.

Other than that, it is fine by me.


> + /* 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);
> --
> 1.7.7.6
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
>


\
 
 \ /
  Last update: 2012-08-17 20:21    [W:0.255 / U:0.136 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site