Re: [PATCH] arm64/vmcore: Add pgtable_l5_enabled information in vmcoreinfo

[Kuan-Ying Lee <kuan-ying.lee@canonical.com>]

On Wed, Aug 28, 2024 at 05:37:07PM +0800, lijiang wrote:
> On Wed, Aug 28, 2024 at 6:48 AM Baoquan He <bhe@redhat.com> wrote:
> 
> > On 08/27/24 at 01:24pm, Will Deacon wrote:
> > > On Mon, Aug 26, 2024 at 02:52:02PM +0800, Kuan-Ying Lee wrote:
> > > > Since arm64 supports 5-level page tables, we need to add this
> > > > information to vmcoreinfo to make debug tools know if 5-level
> > > > page table is enabled or not.
> > > >
> > > > Missing this information will break the debug tool like crash [1].

Sorry, the above line was mistakenly expressed.

Currently, the crash tool doesn't support 4K page with 5-level
page tables (LPA2), so I initially planned to add this
information to implement support for 4K page with 5-level page
table in the crash tool.

> > > >
> > > > [1] https://github.com/crash-utility/crash
> > > >
> > > > Signed-off-by: Kuan-Ying Lee <kuan-ying.lee@canonical.com>
> > > > ---
> > > >  Documentation/admin-guide/kdump/vmcoreinfo.rst | 6 ++++++
> > > >  arch/arm64/kernel/vmcore_info.c                | 3 +++
> > > >  2 files changed, 9 insertions(+)
> > >
> > > In which case, wouldn't you also want to know about pgtable_l4_enabled()?
> >
> > That is a good question. I guess it's deduced in code, mostly needed for
> > different PAGE_OFFSET, how to transfer virtual addr to physical addr,
> > etc.
> >
> >
> Thanks for the information, Baoquan.
> 
> If I understand correctly, for arm64, currently, the crash tool determines
> the levels of the page table based on page size and va_bits, and then
> decides how to translate the address, such as calculating it in conjunction
> with other values, e.g: kernel pgd, offset, etc.

Thanks for the information. I will then try to use VA_BITS to determine
if it is a 5-level page table.
Let me investigate further.

Thanks,
Kuan-Ying Lee

> 
> For more details, please refer to this one:
> https://github.com/crash-utility/crash/blob/master/arm64.c
> 
> 
> Thanks
> Lianbo
> 
> 
> > Add Crash utility experts here.
> >
> >