Re: MMIO ioremap() error with PCI passthrough

[Andy Burns <lists.xensource.com@adslpipe.co.uk>]

On 01/07/2008 10:45, Keir Fraser wrote:

> If you're
> happy changing kernel code, you might try adding printk() instrumentation to
> __ioremap() 

printk(KERN_DEBUG "REMAP: phys=0x%lx, len=%lu\n",
        phys_addr, size);

and __direct_remap_pfn_range() in arch/i386/mm/ioremap-xen.c.

printk(KERN_DEBUG "REMAPPFN: addr=0x%lx, mfn=0x%lx, size=%lu\n",
        address, mfn, size);

> The functions look like they should map the correct range of pages (in this
> case only the page covering FEBFF000-FEBFFFFF)

Built and installed kernel/modules/initrd, rebooted, when it loads the 
saa7134 driver I see this

REMAP: phys=0xfebffc00, len=4096
REMAPPFN: addr=0xffffc20000038000, mfn=0xfebff, size=8192

So the 1K mapping has been rounded up to 4K (x86_64 page size?) before 
passing to __ioremap() and then rounded up again to 8K by the time it 
gets passed to __direct_remap_pfn_range() is that right?

I can manage to build a kernel, but I'm out of my depth in terms of 
knowing what would be good or bad with physical addresses and page 
mappings ...