Messages in this thread | | | Subject | Re: [Fastboot] Re: Kexec on 2.5.59 problems ? | From | (Eric W. Biederman) | Date | 18 Feb 2003 08:06:42 -0700 |
| |
Suparna Bhattacharya <suparna@in.ibm.com> writes:
> Here's the explanation from Anton about why using init_mm is > a problem on ppc64.
Thanks.
> Hi Suparna, > > On ppc64 we have many 2^41B (2 TB) regions: > > USER > KERNEL > VMALLOC > IO > > Why 2TB? Well our three level linux pagetables can map 2TB. The kernel has > no pagetables, so we only need three sets of pagetables. As usual each > user task has its own set of pagetables. So that leaves vmalloc and IO. > > For IO we create our own pgd, ioremap_pgd and for vmalloc we use init_mm. > Why not? Its not being used anywhere else... except for kexec. > > So init_mm covers the region of: > > 0xD000000000000000 to 0xD000000000000000+2^41 > > And what kexec wants is a page under 4GB :)
In this case it definitely wants something identity mapped, which would mean in the first 2TB region. On x86 the limit is 4GB because I only have 32bit pointers. On a 64bit arch that limit should go away.
> Thats why we created another mm.
That makes sense. I guess it boils down to the fact that init_mm is special cased in a number of places and using it I am likely to get me into trouble...
You would not happen to have code that creates a separate mm so I can be lazy would you?
Eric - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |