linux-kernel - Re: [patch]x86: arch_add

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Date:	Tue, 14 Oct 2008 10:09:53 -0700
From:	"Yinghai Lu" <yinghai@...nel.org>
To:	"Shaohua Li" <shaohua.li@...el.com>
Cc:	"Yasunori Goto" <y-goto@...fujitsu.com>,
	lkml <linux-kernel@...r.kernel.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Ingo Molnar" <mingo@...hat.com>
Subject: Re: [patch]x86: arch_add_memory round up address

On Tue, Oct 14, 2008 at 12:30 AM, Shaohua Li <shaohua.li@...el.com> wrote:
> On Tue, Oct 14, 2008 at 01:16:46PM +0800, Yasunori Goto wrote:
>> > On Thu, Oct 09, 2008 at 02:40:34PM +0800, Yinghai Lu wrote:
>> > > On Wed, Oct 8, 2008 at 11:28 PM, Shaohua Li <shaohua.li@...el.com> wrote:
>> > > > On Thu, Oct 09, 2008 at 02:22:50PM +0800, Yinghai Lu wrote:
>> > > >> On Wed, Oct 8, 2008 at 11:08 PM, Shaohua Li <shaohua.li@...el.com> wrote:
>> > > >> > On Thu, 2008-10-09 at 14:04 +0800, Yinghai Lu wrote:
>> > > >> >> On Wed, Oct 8, 2008 at 10:31 PM, Shaohua Li <shaohua.li@...el.com> wrote:
>> > > >> >> > Round up address to a page, otherwise the last page isn't mapped.
>> > > >> >> >
>> > > >> >> > Signed-off-by: Shaohua Li <shaohua.li@...el.com>
>> > > >> >> > ---
>> > > >> >> >  arch/x86/mm/init_64.c |    3 ++-
>> > > >> >> >  1 file changed, 2 insertions(+), 1 deletion(-)
>> > > >> >> >
>> > > >> >> > Index: linux/arch/x86/mm/init_64.c
>> > > >> >> > ===================================================================
>> > > >> >> > --- linux.orig/arch/x86/mm/init_64.c    2008-10-09 11:42:33.000000000 +0800
>> > > >> >> > +++ linux/arch/x86/mm/init_64.c 2008-10-09 11:43:22.000000000 +0800
>> > > >> >> > @@ -721,7 +721,8 @@ int arch_add_memory(int nid, u64 start,
>> > > >> >> >        unsigned long nr_pages = size >> PAGE_SHIFT;
>> > > >> >> >        int ret;
>> > > >> >> >
>> > > >> >> > -       last_mapped_pfn = init_memory_mapping(start, start + size-1);
>> > > >> >> > +       last_mapped_pfn = init_memory_mapping(start,
>> > > >> >> > +               round_up(start + size-1, PAGE_SIZE));
>> > > >> >> >        if (last_mapped_pfn > max_pfn_mapped)
>> > > >> >> >                max_pfn_mapped = last_mapped_pfn;
>> > > >> >>
>> > > >> >> should use
>> > > >> >>
>> > > >> >> last_mapped_pfn = init_memory_mapping(start, start + size);
>> > > >> > No, this still can't guarantee page aligned, though this works in my
>> > > >> > test
>> > > >>
>> > > >> who will call arch_add_memory? that should be start and size already
>> > > >> be page aligned.
>> > > > It's memory hotplug. Doing a round up is always ok and safe even it might be already aligned.
>> > > >
>> > >
>> > > it seems rounding up in that case is wrong...
>> > >
>> > > if the caller call that funtion with extra half page, you don't need
>> > > map that half page, because you can not use it.
>> > shouldn't we mark such page as reserved and so it will not be used? This is the way we handle hole.
>>
>> Just curious,
>> have you ever seen a real machine which needs this patch?
> No, I just did some experiments on a desktop for memory hotplug and this bug
> triggered a crash in my test.
> Yinghai's suggestion also fixed the bug. I just want to have safer method. Anyway, either approach is ok to me.

good, please resubmit updated one with

 last_mapped_pfn = init_memory_mapping(start, start + size);

Thanks

YH
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