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

[Jeremy Fitzhardinge <jeremy@goop.org>]

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.

    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@windriver.com>
> Cc: Wang Chen <wangchen@cn.fujitsu.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Yinghai Lu <yinghai@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
> Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> ---
>  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);
>