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

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On 09/02/2021 15.38, Claudio Imbrenda wrote:
Add support for 1M and 2G pages.

Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
---
  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?

+	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)

 Thomas




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