Re: [PATCH makedumpfile] Align PMD_SECTION_MASK with PHYS_MASK

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On Wed, Mar 18, 2020 at 2:35 AM Michal Suchánek <msuchanek@xxxxxxx> wrote:
>
> On Wed, Mar 18, 2020 at 01:49:05AM +0530, Bhupesh Sharma wrote:
> > On Wed, Mar 18, 2020 at 1:05 AM Michal Suchánek <msuchanek@xxxxxxx> wrote:
> > >
> > > On Tue, Mar 17, 2020 at 02:14:22PM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote:
> > > > Hi Michal,
> > > >
> > > > Thank you for the patch.
> > > >
> > > > > -----Original Message-----
> > > > > Reportedly on some arm64 systems makedumpfile loops forever exhausting
> > > > > all memory when filtering kernel core. It turns out the reason is it
> > > > > cannot resolve some addresses because the PMD mask is wrong. When
> > > > > physical address mask allows up to 48bits pmd mask should allow the
> > > > > same.
> > > > > I suppose you would need a system that needs physical addresses over 1TB
> > > > > to be able to reproduce this. This may be either because you have a lot
> > > > > of memory or because the firmware mapped some memory above 1TB for some
> > > > > reason.
> > > > >
> > > > > Signed-off-by: Michal Suchanek <msuchanek@xxxxxxx>
> > > > > ---
> > > > >  arch/arm64.c | 2 +-
> > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/arch/arm64.c b/arch/arm64.c
> > > > > index 43164ccc32d4..54d60b440850 100644
> > > > > --- a/arch/arm64.c
> > > > > +++ b/arch/arm64.c
> > > > > @@ -81,7 +81,7 @@ static unsigned long kimage_voffset;
> > > > >   * Remove the highest order bits that are not a part of the
> > > > >   * physical address in a section
> > > > >   */
> > > > > -#define PMD_SECTION_MASK   ((1UL << 40) - 1)
> > > > > +#define PMD_SECTION_MASK   ((1UL << PHYS_MASK_SHIFT) - 1)
> > > > >
> > > > >  #define PMD_TYPE_MASK              3
> > > > >  #define PMD_TYPE_SECT              1
> > > > > --
> > > > > 2.23.0
> > > > >
> > > >
> > > > Then I'd prefer to remove PMD_SECTION_MASK and use PHYS_MASK instead.
> > > > Is it OK?  Keeping PMD_SECTION_MASK looks a little confusing to me.
> > >
> > > This code will need to be changed for 52bit support. It remains to be
> > > seen if the mask will be still the same after that. I would go with just
> > > the minimal fix for now to not complicate things.
> >
> > Exactly. I am planning to send out the latest refresh of the kernel
> > and makedumpfile changes for 52-bit makedumpfile/crash support this
> > week.
> >
> > If we can wait for the same, I think it would be better as the code
> > changes/names would be more streamlined and similar to Linux
> > conventions.
> >
> > Please let me know if that makes sense.
>
> I think both is useful. This is a minimal patch that can be applied to
> historical versions of makedumpfile in distributions. This seems to have
> been broken for quite a while already.
>
> And while 52bit support is nice I don't have the hardware to test it so
> it is obviously not that useful for me and many other makedumpfile
> users.

Well the 52-bit changes will still support older CPUs which don't
support the 52-bit ARMv8.2 extensions.
Also as we discussed in the review of the last version, they will
support older kernel + makedumpfile combinations as we need to support
them as well.

In-fact that would be one of the major changes in the latest respin.

However if Kazu is Ok with taking this fix, I have no issues with the
same as well.

Thanks,
Bhupesh


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