Re: [kvm-unit-tests PATCH v1 3/4] s390x: mmu: add support for large pages

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Thu, 11 Feb 2021 11:06:06 +0100
Thomas Huth <thuth@redhat.com> wrote:

> On 09/02/2021 15.38, Claudio Imbrenda wrote:
> > Add support for 1M and 2G pages.
> > 
> > Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> > ---
> >   lib/s390x/mmu.h |  73 +++++++++++++-
> >   lib/s390x/mmu.c | 246
> > +++++++++++++++++++++++++++++++++++++++++++----- 2 files changed,
> > 294 insertions(+), 25 deletions(-)  
> [...]
> > +/*
> > + * Get the pte (page) DAT table entry for the given address and
> > pmd,
> > + * allocating it if necessary.
> > + * The pmd must not be large.
> > + */
> > +static inline pte_t *get_pte(pmd_t *pmd, uintptr_t vaddr)
> > +{
> >   	pte_t *pte = pte_alloc(pmd, vaddr);
> >   
> > -	return &pte_val(*pte);
> > +	assert(!pmd_large(*pmd));
> > +	pte = pte_alloc(pmd, vaddr);  
> 
> Why is this function doing "pte = pte_alloc(pmd, vaddr)" twice now?

ooops! the first pte_alloc is not supposed to be there!
good catch - will fix

> > +	return pte;
> > +}  
> [...]
> > +	if ((level == 1) && !pgd_none(*(pgd_t *)ptr))
> > +		idte_pgdp(va, ptr);
> > +	else if ((level == 2) && !p4d_none(*(p4d_t *)ptr))
> > +		idte_p4dp(va, ptr);
> > +	else if ((level == 3) && !pud_none(*(pud_t *)ptr))
> > +		idte_pudp(va, ptr);
> > +	else if ((level == 4) && !pmd_none(*(pmd_t *)ptr))
> > +		idte_pmdp(va, ptr);
> > +	else if (!pte_none(*(pte_t *)ptr))
> > +		ipte(va, ptr);  
> 
> Meta-comment: Being someone who worked quite a bit with the page
> tables on s390x, but never really got in touch with the way it is
> handled in the Linux kernel, I'm always having a hard time to match
> all these TLAs to the PoP: pmd, pud, p4d ...
> Can we please have a proper place in the kvm-unit-tests sources
> somewhere (maybe at the beginning of mmu.c), where the TLAs are
> explained and how they map to the region and segment tables of the Z
> architecture? (I personally would prefer to completely switch to the
> Z arch naming instead, but I guess that's too much of a change right
> now)

makes sense, I can add that

>   Thomas
>