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    SubjectRe: [PATCH] x86/mm/init: respect memblock reserved regions when destroying mappings
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    On Mon, Feb 7, 2011 at 11:00 AM, Stefano Stabellini
    <stefano.stabellini@eu.citrix.com> wrote:
    > On Mon, 7 Feb 2011, Stefano Stabellini wrote:
    >> On Sun, 6 Feb 2011, Yinghai Lu wrote:
    >> > On 02/05/2011 11:30 PM, H. Peter Anvin wrote:
    >> > > On 02/05/2011 11:02 PM, Yinghai Lu wrote:
    >> > >> why not just move calling cleanup_highmap down?
    >> > >>
    >> > >> something like attached patch.
    >> > >
    >> > > This patch looks very clean and looks on the surface of it like it is
    >> > > removing some ugly ad hoc code, but (as always) it needs a description
    >> > > about the problem it solves and why it is correct.
    >> >
    >> > Sure.
    >> >
    >> >
    >> > Jeremy and xen guys, can you please check if it works well with xen ?
    >> >
    >>
    >> Actually this patch makes things worse on xen, because before
    >> cleanup_highmap() wasn't called at all on xen (on purpose) and now it
    >> is, fully destroying all the mappings we have at _end.
    >>
    >> Can we add a check on memblock reserved regions in cleanup_highmap()?
    >
    > In case you are wondering how Yinghai Lu's patch would look like with
    > the added check, here it is:
    >
    >
    > diff --git a/arch/x86/include/asm/memblock.h b/arch/x86/include/asm/memblock.h
    > index 19ae14b..184f778 100644
    > --- a/arch/x86/include/asm/memblock.h
    > +++ b/arch/x86/include/asm/memblock.h
    > @@ -3,6 +3,7 @@
    >
    >  #define ARCH_DISCARD_MEMBLOCK
    >
    > +bool memblock_check_reserved_size(u64 *addrp, u64 *sizep, u64 align);
    >  u64 memblock_x86_find_in_range_size(u64 start, u64 *sizep, u64 align);
    >  void memblock_x86_to_bootmem(u64 start, u64 end);
    >
    > diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
    > index 975f709..28686b6 100644
    > --- a/arch/x86/include/asm/pgtable_64.h
    > +++ b/arch/x86/include/asm/pgtable_64.h
    > @@ -165,7 +165,7 @@ static inline int pgd_large(pgd_t pgd) { return 0; }
    >  #define __swp_entry_to_pte(x)          ((pte_t) { .pte = (x).val })
    >
    >  extern int kern_addr_valid(unsigned long addr);
    > -extern void cleanup_highmap(void);
    > +extern void cleanup_highmap(unsigned long end);
    >
    >  #define HAVE_ARCH_UNMAPPED_AREA
    >  #define HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
    > diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
    > index 2d2673c..5655c22 100644
    > --- a/arch/x86/kernel/head64.c
    > +++ b/arch/x86/kernel/head64.c
    > @@ -77,9 +77,6 @@ void __init x86_64_start_kernel(char * real_mode_data)
    >        /* Make NULL pointers segfault */
    >        zap_identity_mappings();
    >
    > -       /* Cleanup the over mapped high alias */
    > -       cleanup_highmap();
    > -
    >        max_pfn_mapped = KERNEL_IMAGE_SIZE >> PAGE_SHIFT;
    >
    >        for (i = 0; i < NUM_EXCEPTION_VECTORS; i++) {
    > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
    > index d3cfe26..91afde6 100644
    > --- a/arch/x86/kernel/setup.c
    > +++ b/arch/x86/kernel/setup.c
    > @@ -297,6 +297,9 @@ static void __init init_gbpages(void)
    >  static inline void init_gbpages(void)
    >  {
    >  }
    > +static void __init cleanup_highmap(unsigned long end)
    > +{
    > +}
    >  #endif
    >
    >  static void __init reserve_brk(void)
    > @@ -922,6 +925,9 @@ void __init setup_arch(char **cmdline_p)
    >         */
    >        reserve_brk();
    >
    > +       /* Cleanup the over mapped high alias after _brk_end*/
    > +       cleanup_highmap(_brk_end);
    > +
    >        memblock.current_limit = get_max_mapped();
    >        memblock_x86_fill();
    >
    > diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
    > index 947f42a..f13ff3a 100644
    > --- a/arch/x86/mm/init.c
    > +++ b/arch/x86/mm/init.c
    > @@ -279,25 +279,6 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
    >        load_cr3(swapper_pg_dir);
    >  #endif
    >
    > -#ifdef CONFIG_X86_64
    > -       if (!after_bootmem && !start) {
    > -               pud_t *pud;
    > -               pmd_t *pmd;
    > -
    > -               mmu_cr4_features = read_cr4();
    > -
    > -               /*
    > -                * _brk_end cannot change anymore, but it and _end may be
    > -                * located on different 2M pages. cleanup_highmap(), however,
    > -                * can only consider _end when it runs, so destroy any
    > -                * mappings beyond _brk_end here.
    > -                */
    > -               pud = pud_offset(pgd_offset_k(_brk_end), _brk_end);
    > -               pmd = pmd_offset(pud, _brk_end - 1);
    > -               while (++pmd <= pmd_offset(pud, (unsigned long)_end - 1))
    > -                       pmd_clear(pmd);
    > -       }
    > -#endif
    >        __flush_tlb_all();
    >
    >        if (!after_bootmem && e820_table_end > e820_table_start)
    > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
    > index 71a5929..028c49e 100644
    > --- a/arch/x86/mm/init_64.c
    > +++ b/arch/x86/mm/init_64.c
    > @@ -297,18 +297,26 @@ void __init init_extra_mapping_uc(unsigned long phys, unsigned long size)
    >  * rounded up to the 2MB boundary. This catches the invalid pmds as
    >  * well, as they are located before _text:
    >  */
    > -void __init cleanup_highmap(void)
    > +void __init cleanup_highmap(unsigned long end)
    >  {
    >        unsigned long vaddr = __START_KERNEL_map;
    > -       unsigned long end = roundup((unsigned long)_end, PMD_SIZE) - 1;
    >        pmd_t *pmd = level2_kernel_pgt;
    >        pmd_t *last_pmd = pmd + PTRS_PER_PMD;
    > +       u64 size, addrp;
    > +       bool changed;
    > +
    > +       end = roundup(end, PMD_SIZE) - 1;
    >
    >        for (; pmd < last_pmd; pmd++, vaddr += PMD_SIZE) {
    >                if (pmd_none(*pmd))
    >                        continue;
    > -               if (vaddr < (unsigned long) _text || vaddr > end)
    > -                       set_pmd(pmd, __pmd(0));
    > +               if (vaddr < (unsigned long) _text || vaddr > end) {
    > +                       addrp = __pa(vaddr);
    > +                       size = PMD_SIZE;
    > +                       changed = memblock_check_reserved_size(&addrp, &size, PMD_SIZE);
    > +                       if (!changed && size)
    > +                               set_pmd(pmd, __pmd(0));
    > +               }

    for native path, memblock_check_reserved_size() are called 256 times
    without obvious reasons.

    Yinghai
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