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Date: Mon, 07 Feb 2011 20:56:26 -0800
From: Jeremy Fitzhardinge <jeremy@...p.org>
To: Yinghai Lu <yinghai@...nel.org>
CC: Stefano Stabellini <stefano.stabellini@...citrix.com>,
"H. Peter Anvin" <hpa@...or.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"x86@...nel.org" <x86@...nel.org>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Jan Beulich <JBeulich@...ell.com>
Subject: Re: [PATCH] x86/mm/init: respect memblock reserved regions when destroying
mappings
On 02/07/2011 07:12 PM, Yinghai Lu wrote:
> On 02/07/2011 01:56 PM, Jeremy Fitzhardinge wrote:
>> On 02/07/2011 11:00 AM, Yinghai Lu wrote:
>>> On 02/07/2011 10:58 AM, Stefano Stabellini wrote:
>>>> On Mon, 7 Feb 2011, Yinghai Lu wrote:
>>>>> On 02/07/2011 08:50 AM, 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()?
>>>>>> Otherwise could we avoid calling cleanup_highmap() at all on xen?
>>>>> why DO xen need over-mapped kernel initial mapping?
>>>>>
>>>>> what is in that range after _end to 512M?
>>>> The mfn list that is the list of machine frame numbers assigned to this
>>>> domain; it is used across the kernel to convert pfns into mfns.
>>>> It passed to us at that address by the domain builder.
>>> is it possible for you to pass physical address, and then map it in kernel?
>> That is possible in principle, but very difficult in practice.
>>
>> What's wrong with honouring reserved memory ranges under all circumstances?
> why punishing native path with those checking?
Why is it punishing anyone to expect memory reservations to be observed?
> please check if
>
> + * max_pfn_mapped is set to KERNEL_IMAGE_SIZE >> PAGE_SHIFT in
> + * head64.c::x86_start_kernel(), aka native path
> + */
> + if (max_pfn_mapped != (KERNEL_IMAGE_SIZE >> PAGE_SHIFT))
> + return;
>
> could be used to skip clear highmap for xen path?
Seems pretty ad-hoc.
J
> Thanks
>
> Yinghai
>
>
>
> [PATCH -v2] x86: Cleanup highmap after brk is concluded
>
> Now cleanup_high actually is two steps. one is early in head64.c.
> and it only clear above _end. later will try to clean from _brk_end to _end.
> it will need to double check if those boundary are PMD_SIZE aligned...
>
> Also init_memory_mapping() are called several times for numa or memory hotplug.
> and it deals real memory mapping instead of initial kernel mapping.
> We really should not handle initial kernel mapping there.
>
> We can move cleanup_highmap() calling down after _brk_end is settled and pass
> _brk_end with it.
>
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>
> ---
> arch/x86/include/asm/pgtable_64.h | 2 +-
> arch/x86/kernel/head64.c | 3 ---
> arch/x86/kernel/setup.c | 6 ++++++
> arch/x86/mm/init.c | 19 -------------------
> arch/x86/mm/init_64.c | 20 +++++++++++++++-----
> 5 files changed, 22 insertions(+), 28 deletions(-)
>
> Index: linux-2.6/arch/x86/include/asm/pgtable_64.h
> ===================================================================
> --- linux-2.6.orig/arch/x86/include/asm/pgtable_64.h
> +++ linux-2.6/arch/x86/include/asm/pgtable_64.h
> @@ -165,7 +165,7 @@ static inline int pgd_large(pgd_t pgd) {
> #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
> Index: linux-2.6/arch/x86/kernel/head64.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/head64.c
> +++ linux-2.6/arch/x86/kernel/head64.c
> @@ -77,9 +77,6 @@ void __init x86_64_start_kernel(char * r
> /* 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++) {
> Index: linux-2.6/arch/x86/kernel/setup.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/setup.c
> +++ linux-2.6/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();
>
> Index: linux-2.6/arch/x86/mm/init.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/mm/init.c
> +++ linux-2.6/arch/x86/mm/init.c
> @@ -279,25 +279,6 @@ unsigned long __init_refok init_memory_m
> 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)
> Index: linux-2.6/arch/x86/mm/init_64.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/mm/init_64.c
> +++ linux-2.6/arch/x86/mm/init_64.c
> @@ -297,12 +297,22 @@ void __init init_extra_mapping_uc(unsign
> * 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;
> + unsigned long vaddr;
> + pmd_t *pmd, *last_pmd;
> +
> + /*
> + * max_pfn_mapped is set to KERNEL_IMAGE_SIZE >> PAGE_SHIFT in
> + * head64.c::x86_start_kernel(), aka native path
> + */
> + if (max_pfn_mapped != (KERNEL_IMAGE_SIZE >> PAGE_SHIFT))
> + return;
> +
> + vaddr = __START_KERNEL_map;
> + pmd = level2_kernel_pgt;
> + last_pmd = pmd + PTRS_PER_PMD;
> + end = roundup(end, PMD_SIZE) - 1;
>
> for (; pmd < last_pmd; pmd++, vaddr += PMD_SIZE) {
> if (pmd_none(*pmd))
>
--
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