Date: Thu, 14 Sep 2006 19:59:10 -0400
From: Vivek Goyal <vgoyal@in.ibm.com>
To: keith mannthey <kmannth@us.ibm.com>
Cc: dave hansen <haveblue@us.ibm.com>, lkml <linux-kernel@vger.kernel.org>,
       ebiederm@xmission.com, andrew <akpm@osdl.org>
Subject: Re: [Bug] 2.6.18-rc6-mm2 i386 trouble finding RSDT in get_memcfg_from_srat
Message-ID: <20060914235910.GG25044@in.ibm.com>
Reply-To: vgoyal@in.ibm.com
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On Thu, Sep 14, 2006 at 04:43:33PM -0700, keith mannthey wrote:
> On Thu, 2006-09-14 at 16:21 -0700, Dave Hansen wrote:
> > On Thu, 2006-09-14 at 19:04 -0400, Vivek Goyal wrote:
> > > I think I know what is going on wrong here. boot_ioremap() is assuming 
> > > that only first 8MB of physical memory is being mapped and while
> > > calculating the index into page table (boot_pte_index) we will truncate
> > > any higher address bits. 
> > 
> > Vivek, are those pte pages still all contiguous?
> > 
> > Yeah, that's probably it.  Keith, I'm trying to think of reasons why we
> > need the mask here:
> > 
> > #define boot_pte_index(address) \
> >              (((address) >> PAGE_SHIFT) & (BOOT_PTE_PTRS - 1))
> > 
> > and I can't think of any other than just masking out the top of the
> > virtual address.  You could do this a bunch of other ways, like __pa().
> > 
> > This might just work:
> > 
> > static unsigned long boot_pte_index(unsigned long vaddr)
> > {
> > 	return __pa(vaddr) >> PAGE_SHIFT;
> > }
> With 
> CONFIG_KEXEC=y
> CONFIG_CRASH_DUMP=y
> CONFIG_PHYSICAL_START=0x1000000
> and the above __pa(vaddr) >> PAGE_SHIFT changed things worked for me but
> I am still confused as to why the pte we set is c1686f6c and we flush
> and return c13db000. 

I think c13db000 is the virtual address of symbol boot_ioremap_space,
and we are remapping this virtual address to physical addres eff9c063,
that's why we flush tlb for this virtual address.

I guess c1686f6c is virtual address of PTE (somewhere between pg0 to pg5).
It is independent of actual virtual address (boot_ioremap_space) being
remapped.  

Thanks
Vivek

> 
> get_memcfg_from_srat: assigning address to rsdp fdfc0
> RSD PTR  v0 [IBM   ]
> rsdp->rsdt_address eff9c2c0
> boot_ioremap phys_addr = eff9c2c0 long = 44
> __boot_ioremap phys_addr = eff9c000 pages = 1 source c13db000
> setting pte  c1686f6c to eff9c063
> just flushed c13db000
> boot_ioremap and I return c13db2c0
> rsdt = c13db2c0 header is RSDT4
> Begin SRAT table scan....
> 
> thanks,
>   Keith 
> 
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