Re: [PATCH v3] x86: let 'reservetop' functioning right

[Liang Li]

On Thu, Apr 08, 2010 at 08:12:18PM -0700, Jeremy Fitzhardinge wrote:
> On 04/08/2010 05:43 PM, Liang Li wrote:
> > When specify 'reservetop=0xbadc0de' kernel parameter, the kernel will
> > stop booting due to a early_ioremap bug that relate to commit 8827247ff.
> >
> > The root cause of boot failure problem is the value of 'slot_virt[i]'
> > was initialized in setup_arch->early_ioremap_init. But later in
> > setup_arch, the function 'parse_early_param' will modify 'FIXADDR_TOP'
> > when 'reservetop=0xbadc0de' being specified.
> >
> > The simplest fix might be use __fix_to_virt(idx0) to get updated value
> > of 'FIXADDR_TOP' in '__early_ioremap' instead of reference old value
> > from slot_virt[slot] directly.
> >   
> 
> While I guess this patch works OK, I have to say that I'm worried by the
> need for it at all; it seems to be papering over a more serious
> problem.  reserve_top_address() is supposed to be called very early,
> before anything has used or referenced FIXADDR_TOP.  If we're seeing
> problems with FIXADDR_TOP changing after it has been used, then it means
> that reserve_top_address() is being called too late.  Fixing that would
> be the real fix.

The ideal thing is FIXADDR_TOP should not be touched after
early_ioremap_init. The late call to reserve_top_address is from
parse_reservetop, aka when reservetop=0xabcd0000 being passed as kernel
commandline parameter. In setup_arch, the call sequence is:

setup_arch
  -> early_ioremap_init
  -> parse_early_param
    -> parse_reservetop
	  ->reserve_top_address

See, how could we solve the confliction better?

Best regards,
	 -Liang Li

> 
>     J
> 
> > Changelog since v0:
> >
> > -v1: When reservetop being handled then FIXADDR_TOP get adjusted, Hence
> > check prev_map then re-initialize slot_virt and PMD based on new
> > FIXADDR_TOP.
> >
> > -v2: place fixup_early_ioremap hence call early_ioremap_init in
> > reserve_top_address  to re-initialize slot_virt and corresponding PMD
> > when parse_reservetop
> >
> > -v3: move fixup_early_ioremap out of reserve_top_address to make sure
> > other clients of reserve_top_address like xen/lguest won't broken
> >
> > Signed-off-by: Liang Li <liang.li@xxxxxxxxxxxxx>
> > Cc: Wang Chen <wangchen@xxxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
> > Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > ---
> >  arch/x86/include/asm/io.h |    1 +
> >  arch/x86/mm/ioremap.c     |   15 +++++++++++++++
> >  arch/x86/mm/pgtable_32.c  |    1 +
> >  3 files changed, 17 insertions(+), 0 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
> > index a1dcfa3..30a3e97 100644
> > --- a/arch/x86/include/asm/io.h
> > +++ b/arch/x86/include/asm/io.h
> > @@ -347,6 +347,7 @@ extern void __iomem *early_ioremap(resource_size_t phys_addr,
> >  extern void __iomem *early_memremap(resource_size_t phys_addr,
> >  				    unsigned long size);
> >  extern void early_iounmap(void __iomem *addr, unsigned long size);
> > +extern void fixup_early_ioremap(void);
> >  
> >  #define IO_SPACE_LIMIT 0xffff
> >  
> > diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> > index 5eb1ba7..e4ab706 100644
> > --- a/arch/x86/mm/ioremap.c
> > +++ b/arch/x86/mm/ioremap.c
> > @@ -448,6 +448,21 @@ static inline void __init early_clear_fixmap(enum fixed_addresses idx)
> >  static void __iomem *prev_map[FIX_BTMAPS_SLOTS] __initdata;
> >  static unsigned long prev_size[FIX_BTMAPS_SLOTS] __initdata;
> >  
> > +void __init fixup_early_ioremap(void)
> > +{
> > +	int i;
> > +	for (i = 0; i < FIX_BTMAPS_SLOTS; i++) {
> > +		if (prev_map[i])
> > +			break;
> > +	}
> > +
> > +	if (i < FIX_BTMAPS_SLOTS)
> > +		BUG_ON(1);
> > +
> > +	early_ioremap_init();
> > +	return;
> > +}
> > +
> >  static int __init check_early_ioremap_leak(void)
> >  {
> >  	int count = 0;
> > diff --git a/arch/x86/mm/pgtable_32.c b/arch/x86/mm/pgtable_32.c
> > index 1a8faf0..26eadaa 100644
> > --- a/arch/x86/mm/pgtable_32.c
> > +++ b/arch/x86/mm/pgtable_32.c
> > @@ -128,6 +128,7 @@ static int __init parse_reservetop(char *arg)
> >  
> >  	address = memparse(arg, &arg);
> >  	reserve_top_address(address);
> > +	fixup_early_ioremap();
> >  	return 0;
> >  }
> >  early_param("reservetop", parse_reservetop);
> >   
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