Hello,
On Sun, 2025-08-24 at 23:09 +0200, John Paul Adrian Glaubitz wrote:
> First, let's start with the bugs. For a while it has been known that recent
> kernel
> versions can be very unstable on certain SPARC machines, this has been
> observed in
> particular with UltraSPARC III CPUs but also on certain newer CPUs such as
> SPARC T1.
>
> After I started bisecting the issue, I ran into multiple false positives
> until I
> identified d53d2f78cead as the culprit which makes use of a new vmalloc flag
> called
> VM_FLUSH_RESET_PERMS.
>
> However, this particular change is actually not broken but rather just
> uncovered the
> original bug. The introduction of VM_FLUSH_RESET_PERMS allowed the kernel to
> flush
> TLBs earlier after booting and more often. And since the original problem was
> suspected
> with the TLB flush management on SPARC, it was just natural that the change
> in d53d2f78cead
> turned out in the bisect.
>
> Further investigation showed that the actual culprit are the CPU-specific
> implementations
> of copy_{from,to}_user which can be found in arch/sparc/lib. These are broken
> on different
> CPU types to a different degree which explains perfectly fine why recent
> kernels are more
> unstable on certain CPU types than on others.
>
> Luckily, Michael Karcher has already made good progress in investigating and
> fixing these
> bugs so that, for example, a trial patch for the UltraSPARC III showed that a
> simple
> one-line change would fix all the stability issues currently seen on these
> CPU types.
>
> It is expected that a series of patches will follow shortly that will address
> the bugs in
> the copy_{from,to}_user on all affected CPU types. In the mean time, it
> should be possible
> to switch the kernel to the generic code for copy_{from,to}_user that can be
> found in the
> same source directory to get a stable system on any CPU type.
A patch series to address these bugs was just posted:
https://lore.kernel.org/all/[email protected]/
Please test and report back!
Adrian
--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer
`. `' Physicist
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
