Messages in this thread Patch in this message | | | Date | Sun, 16 Nov 2014 20:00:16 -0800 | Subject | Re: [PATCH v2] x86, mm: set NX across entire PMD at boot | From | Yinghai Lu <> |
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On Sun, Nov 16, 2014 at 3:44 PM, Thomas Gleixner <tglx@linutronix.de> wrote: > > _brk_end is adjusted at boot time via extend_brk() up to __brk_limit, > which is the same as _end. We usually do not use all of that space. So > it's expected that _brk_end < _end. > >> Is this correct? It sounded like tglx wanted the pmd split, like this: > > Yes, I wanted to get rid of the high mapping for anything between > _brk_end and _end, and I brought you on the wrong track with my > suggestion to call free_init_pages(). Sorry about that.
:)
> > That happened because I missed the completely non obvious fact, that > only the effective brk section is reserved for the kernel via > reserve_brk(). So the area between _brk_end and _end is already > reusable. Though that reuse works only by chance and not by design and > is completely undocumented as everything else in that area.
where is info for everything else?
> > So the initial patch to get rid of the X mapping is of course to just > extend the area to the PMD. A little bit different to your initial > patch, but essentially the same. > > - unsigned long all_end = PFN_ALIGN(&_end); > + unsigned long all_end = roundup((unsigned long) &_end, PMD_SIZE); > > I'm going to apply your V1 patch with the above roundup() > simplification. If a page of that area gets used later on then we are > going to split up the PMD anyway.
should use _brk_end instead of &_end for the roundup?
> > But still we want to get rid of that highmap between _brk_end and > _end, but there is absolutely no reason to come up with extra silly > functions for that. > > So the obvious solution is to let setup_arch() reserve the memory up > to _end instead of _bss_stop, get rid of the extra reservation in > reserve_brk() and then let free_initmem() release the area between > _brk_end and _end. No extra hackery, no side effects, just works.
So where get the highmap to be removed? free_init_pages via free_initmem()?
with the code change like you suggested,
--- arch/x86/kernel/setup.c | 6 +----- arch/x86/mm/init.c | 6 ++++++ arch/x86/mm/init_64.c | 2 +- 3 files changed, 8 insertions(+), 6 deletions(-)
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 @@ -286,10 +286,6 @@ static void __init cleanup_highmap(void)
static void __init reserve_brk(void) { - if (_brk_end > _brk_start) - memblock_reserve(__pa_symbol(_brk_start), - _brk_end - _brk_start); - /* Mark brk area as locked down and no longer taking any new allocations */ _brk_start = 0; @@ -857,7 +853,7 @@ dump_kernel_offset(struct notifier_block void __init setup_arch(char **cmdline_p) { memblock_reserve(__pa_symbol(_text), - (unsigned long)__bss_stop - (unsigned long)_text); + (unsigned long)_end - (unsigned long)_text);
early_reserve_initrd();
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 @@ -1122,7 +1122,7 @@ void mark_rodata_ro(void) unsigned long end = (unsigned long) &__end_rodata_hpage_align; unsigned long text_end = PFN_ALIGN(&__stop___ex_table); unsigned long rodata_end = PFN_ALIGN(&__end_rodata); - unsigned long all_end = PFN_ALIGN(&_end); + unsigned long all_end = roundup((unsigned long)&_end, PMD_SIZE);
printk(KERN_INFO "Write protecting the kernel read-only data: %luk\n", (end - start) >> 10); 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 @@ -637,9 +637,15 @@ void free_init_pages(char *what, unsigne
void free_initmem(void) { + unsigned long all_end = roundup((unsigned long)&_end, PMD_SIZE); + free_init_pages("unused kernel", (unsigned long)(&__init_begin), (unsigned long)(&__init_end)); + +#ifdef CONFIG_X86_64 + free_init_pages("unused brk", PFN_ALIGN(_brk_end), all_end); +#endif }
#ifdef CONFIG_BLK_DEV_INITRD
got [ 7.942636] Freeing unused brk memory: 500K (ffffffff84383000 - ffffffff84400000) ---[ High Kernel Mapping ]--- 0xffffffff80000000-0xffffffff81000000 16M pmd 0xffffffff81000000-0xffffffff82200000 18M ro PSE GLB x pmd 0xffffffff82200000-0xffffffff82c00000 10M ro PSE GLB NX pmd 0xffffffff82c00000-0xffffffff82e00000 2M RW PSE GLB NX pmd 0xffffffff82e00000-0xffffffff83000000 2M RW GLB NX pte 0xffffffff83000000-0xffffffff83200000 2M RW PSE GLB NX pmd 0xffffffff83200000-0xffffffff83400000 2M RW GLB NX pte 0xffffffff83400000-0xffffffff84200000 14M RW PSE GLB NX pmd 0xffffffff84200000-0xffffffff84400000 2M RW GLB NX pte 0xffffffff84400000-0xffffffffa0000000 444M pmd the _brk_end to &_end highmap is still there
Also if you want to remove highmap between _brk_end and _end, Do you want highmap for [text_end, rodata_start) [rodata_end, _sdata), as mark_rodata_ro is calling
free_init_pages("unused kernel", (unsigned long) __va(__pa_symbol(text_end)), (unsigned long) __va(__pa_symbol(rodata_start))); free_init_pages("unused kernel", (unsigned long) __va(__pa_symbol(rodata_end)), (unsigned long) __va(__pa_symbol(_sdata)));
Thanks
Yinghai
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