Re: [PATCH] vmalloc: Don't use flush flag when no exec perm

[Meelis Roos]

> > The addition of VM_FLUSH_RESET_PERMS for BPF JIT allocations was
> > bisected to prevent boot on an UltraSparc III machine. It was found
> > that
> > sometime shortly after the TLB flush this flag does on vfree of the
> > BPF
> > program, the machine hung. Further investigation showed that before
> > any of
> > the changes for this flag were introduced, with
> > CONFIG_DEBUG_PAGEALLOC
> > configured (which does a similar TLB flush of the vmalloc range on
> > every vfree), this machine also hung shortly after the first vmalloc
> > unmap/free.
> >
> > So the evidence points to there being some existing issue with the
> > vmalloc TLB flushes, but it's still unknown exactly why these hangs
> > are
> > happening on sparc. It is also unknown when someone with this
> > hardware
> > could resolve this, and in the meantime using this flag on it turns a
> > lurking behavior into something that prevents boot.
>
> The sparc TLB flush issue has been bisected and is being worked on now,
> so hopefully we won't need this patch:
> https://marc.info/?l=linux-sparc&m=155915694304118&w=2

And the sparc64 patch that fixes CONFIG_DEBUG_PAGEALLOC also fixes booting
of the latest git kernel on Sun V445 where my problem initially happened.

--
Meelis Roos <mroos@xxxxxxxx>