Re: [RFC PATCH] ARM: Support allocating crashkernel above 4G for LPAE

[Baoquan He <bhe@redhat.com>]

On 08/05/24 at 09:23am, Jinjie Ruan wrote:
> 
> 
> On 2024/8/2 19:01, Russell King (Oracle) wrote:
> > On Fri, Aug 02, 2024 at 05:25:10PM +0800, Jinjie Ruan wrote:
> >> As ARM LPAE feature support accessing memory beyond the 4G limit, define
> >> HAVE_ARCH_CRASHKERNEL_RESERVATION_HIGH macro to support reserving crash
> >> memory above 4G for ARM32 LPAE.
> >>
> >> No test because there is no LPAE ARM32 hardware.
> > 
> > Why are you submitting patches for features you can't test?
> > 
> > I'm not going to apply this without it being properly tested, because I
> > don't believe that this will work in the generic case.
> > 
> > If the crash kernel is located in memory outside of the lower 4GiB of
> > address space, and there is no alias within physical address space
> > for that memory, then there is *no* *way* for such a kernel to boot.
> 
> I'm sorry that I released this patch without testing it. I actually
> intended to bring up this issue for discussion. If anyone has the
> environment to test it, that would be great. In the meantime, we could
> have a discussion on the significance and relevance of this approach.

I don't know arm32 and its LPAE. I know a little about x86_32 where
crashkernel can only be reserved below 896M because of the virtual
memory layout, and all memory above that is high memory which can't be
used as kernel memory directly. So from this patch, arm32 is different
than x86_32.

> 
> > 
> > So, right now I believe this patch to be *fundamentally* wrong.
> > 
>