linux-kernel - Re: [PATCH 1/2] x86 boot: add E820_RESVD

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Message-Id: <1214812303.3187.10.camel@caritas-dev.intel.com>
Date:	Mon, 30 Jun 2008 15:51:43 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, andi@...stfloor.org,
	mingo@...hat.com, tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86 boot: add E820_RESVD_KERN

On Mon, 2008-06-30 at 00:34 -0700, Yinghai Lu wrote:
> On Mon, Jun 30, 2008 at 12:03 AM, Huang, Ying <ying.huang@...el.com> wrote:
> > On Fri, 2008-06-27 at 15:05 -0700, Yinghai Lu wrote:
> >> On Thu, Jun 26, 2008 at 7:48 PM, Huang, Ying <ying.huang@...el.com> wrote:
> >> > On Thu, 2008-06-26 at 19:22 -0700, Yinghai Lu wrote:
> >> >> On Thu, Jun 26, 2008 at 2:47 AM, Yinghai Lu <yhlu.kernel@...il.com> wrote:
> >> >> > On Thu, Jun 26, 2008 at 12:48 AM, Huang, Ying <ying.huang@...el.com> wrote:
> >> >> >> On Thu, 2008-06-26 at 00:25 -0700, Yinghai Lu wrote:
> >> >> >> [...]
> >> >> >>> >                if (pfn >= limit_pfn)
> >> >> >>> > @@ -977,7 +978,7 @@ u64 __init early_reserve_e820(u64 startt
> >> >> >>> >                return 0;
> >> >> >>> >
> >> >> >>> >        addr = round_down(start + size - sizet, align);
> >> >> >>> > -       e820_update_range(addr, sizet, E820_RAM, E820_RESERVED);
> >> >> >>> > +       e820_update_range(addr, sizet, E820_RAM, E820_RESVD_KERN);
> >> >> >>>
> >> >> >>> this line is not needed.
> >> >> >>
> >> >> >> Why? Memory reserved by early_rserved_e820 should not be saved during
> >> >> >> hibernation? shoudl not be saved by kdump?
> >> >> >>
> >> >
> >> > Can you tell me why this line is not needed?
> >> >
> >> > [...]
> >> >> some like the attach patch...
> >> >>
> >> >> you still can merge parse_setup_data parse_e820_ext
> >> >> also entries in parse_e820_ext is not initialized..., __copy_e820_map
> >> >> will do nothing.
> >> >
> >> > OK. Because some E820 entries are available after parse_setup_data(),
> >> > it is better to call reserve_setup_data() after calling
> >> > parse_setup_data() if update_e820_range() is used instead of
> >> > reserve_early().
> >>
> >> please modify it and test on your platforms then submit to Ingo..
> >
> > It seems that there is an issue:
> >
> > - If parse_setup_data() is called before reserve_setup_data(), and there
> > is a conflict between memory area used by setup_data and other memory
> > area, it is possible that the contents of setup_data is changed. So that
> > system may panic before reporting memory area conflict. And it seems
> > that memory area conflict is not checked by e820_update_range().
> 
> what is "other memory area"? returned from find_e820_area? no one use that yet.

I mean memory area reserved with reserved_early() or e820_update_range()
before reserve_setup_data() is called.

And because there is no conflict check in e820_update_range(), what to
deal with potential conflict between setup_data and other memory area
regardless which one is reserved earlier?


Another issue related:

Because some memmap entries are available via extended E820 memmap
(SETUP_E820_EXT), it is not strictly safe to use e820_update_range()
between setup_memory_map() and parse_setup_data(). It may be better to
parse extended E820 memmap right after setup_memory_map().

Best Regards,
Huang Ying
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