Re: [PATCH] sparc64: fix hugetlb for sun4u

[John Paul Adrian Glaubitz]

Hi Anthony,

On Wed, 2025-07-16 at 08:18 +0200, John Paul Adrian Glaubitz wrote:
> On Tue, 2025-07-15 at 18:24 -0700, Anthony Yznaga wrote:
> > An attempt to exercise sparc hugetlb code in a sun4u-based guest
> > running under qemu results in the guest hanging due to being stuck
> > in a trap loop. This is due to invalid hugetlb TTEs being installed
> > that do not have the expected _PAGE_PMD_HUGE and page size bits set.
> > Although the breakage has gone apparently unnoticed for several years,
> > fix it now so there is the option to exercise sparc hugetlb code under
> > qemu. This can be useful because sun4v support in qemu does not support
> > linux guests currently and sun4v-based hardware resources may not be
> > readily available.
> 
> It has actually been observed for a long time that newer kernels are
> unstable on sun4u while there are no stability issues on sun4v.

Just as a heads-up: I'm currently building a Debian kernel with this patch
and see if this fixes the stability issues we're seeing on UltraSPARC machines.

> I'm not sure though whether the Debian kernel enables hugetlb by default.

We do.

I'll report back.

Adrian

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