Question about Address Range Validation in Crash Kernel Allocation

[Baoquan He]

On 03/19/24 at 07:24am, chenhaixiang (A) wrote:
> Thank you for your reply!
> The kernel version on my machine is kernel-5.10, and the kexec-tools version is kexec-tools-2.0.27. 
> However, my issue seems to be a bit different. On my machine, I can see the crashkernel memory segment in /proc/iomem. However, for some reason, within the address range allocated for crashkernel, there is also a segment marked as 'Reserved' (I'm not sure who marked it). In this scenario, kexec-tools calculates the CRASH MEMORY RANGES incorrectly.
> ```

crashkernel region can't be reserved again once it's allocated and
reserved in memblock. There must be something wrong with the code. You
can try upstream kernel and kexec-tools to see if it exists too. Since
you are using an old kernel and could be on a distros, we may not be
able to cover it. Sorry about that.

If you want to debug to find out the reason, I can help give suggestions.

> cat /proc/iomem
> 2d4fd058-58ffffff : System RAM
>   49000000-58ffffff : Crash kernel
>     53cbd000-53ccffff : Reserved
> ```
> I'm not sure if the crashkernel memory segment should not include other markings, and if not supported, whether kexec-tools should raise an error.
> Thanks
> Chen Haixiang
> ----------
> On 03/19/24 at 9:38qm, Baoquan He wrote:
> > Hi,
> > 
> > On 03/18/24 at 12:00pm, chenhaixiang (A) wrote:
> > > Dear kexec Community Members,
> > >
> > > I encountered an issue while using kexec-tools on my x86_64 machine.
> > > When there is a segment marked as 'reserved' within the memory range
> > allocated for the crash kernel in /proc/iomem,the output appears as follows:
> > > 2d4fd058-60efefff : System RAM
> > >   2d4fd058-58ffffff : System RAM
> > >     49000000-58ffffff : Crash kernel
> > >       53cbd000-53ccffff : Reserved
> > 
> > What kernel are you using? the version of kernel, and kexec-tools?
> > 
> > If you are testing on the latest mainline kernel, you could meet the issue Dave
> > have met and fixed in below patch:
> > 
> > [PATCH] x86/kexec: do not update E820 kexec table for setup_data
> > https://lore.kernel.org/all/ZeZ2Kos-OOZNSrmO@darkstar.users.ipa.redhat.com/
> > T/#u
> > 
> > Thanks
> > Baoquan
> > 
> > >
> > > The crash_memory_range array will encounter incorrect address ranges:
> > > CRASH MEMORY RANGES
> > > 000000002d4fd058-0000000048ffffff (0)
> > > 0000000053cbd000-0000000048ffffff (1)
> > > 0000000059000000-0000000053ccffff (0)
> > >
> > > Read the code, I noticed that the get_crash_memory_ranges() function
> > invokes exclude_region() to handle the splitting of memory regions, but it seems
> > unable to properly handle the scenario described above.
> > > The code logic is as follows:
> > > ...
> > > 	if (start < mend && end > mstart) {
> > > 		if (start != mstart && end != mend) {
> > > 			/* Split memory region */
> > > 			crash_memory_range[i].end = start - 1;
> > > 			temp_region.start = end + 1;
> > > 			temp_region.end = mend;
> > > 			temp_region.type = RANGE_RAM;
> > > 			tidx = i+1;
> > > 		} else if (start != mstart)
> > > 			crash_memory_range[i].end = start - 1;
> > > 		else
> > > 			crash_memory_range[i].start = end + 1;
> > > 	}
> > > ...
> > > If start < mstart < mend < end, resulting in crash_memory_range[i].end
> > becoming less than crash_memory_range[i].start, leading to incorrect address
> > ranges.
> > > I would like to know if this behavior is reasonable and whether it is necessary to
> > validate the address ranges for compliance at the end.
> > >
> > > Thank you for your time and assistance.
> > >
> > > Chen Haixiang
> > >
> > > _______________________________________________
> > > kexec mailing list
> > > kexec at lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/kexec
> > >
>