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riscv: handle kernel PTE edge-case in pmap_enter_l2()

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Page table pages are never freed from the kernel pmap, instead they are
zeroed when a range is unmapped. This allows future mappings to be
constructed more quickly. Detect this scenario in pmap_enter_l2(), so we
don't fail to create a superpage mapping when the 2MB range is actually
available.

Reviewed by:	markj
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D36885
This commit is contained in:
Mitchell Horne 2022-10-05 13:14:36 -03:00
parent 99fe523778
commit 1f9cc5ffc5
1 changed files with 20 additions and 1 deletions
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21
sys/riscv/riscv/pmap.c
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@ -3146,6 +3146,24 @@ pmap_enter_2mpage(pmap_t pmap, vm_offset_t va, vm_page_t m, vm_prot_t prot,
PMAP_ENTER_NOREPLACE | PMAP_ENTER_NORECLAIM, NULL, lockp));
}
/*
* Returns true if every page table entry in the specified page table is
* zero.
*/
static bool
pmap_every_pte_zero(vm_paddr_t pa)
{
pt_entry_t *pt_end, *pte;
KASSERT((pa & PAGE_MASK) == 0, ("pa is misaligned"));
pte = (pt_entry_t *)PHYS_TO_DMAP(pa);
for (pt_end = pte + Ln_ENTRIES; pte < pt_end; pte++) {
if (*pte != 0)
return (false);
}
return (true);
}
/*
* Tries to create the specified 2MB page mapping. Returns KERN_SUCCESS if
* the mapping was created, and one of KERN_FAILURE, KERN_NO_SPACE, or
@ -3190,7 +3208,8 @@ pmap_enter_l2(pmap_t pmap, vm_offset_t va, pd_entry_t new_l2, u_int flags,
"pmap_enter_l2: no space for va %#lx"
" in pmap %p", va, pmap);
return (KERN_NO_SPACE);
} else {
} else if (va < VM_MAXUSER_ADDRESS ||
!pmap_every_pte_zero(L2PTE_TO_PHYS(oldl2))) {
l2pg->ref_count--;
CTR2(KTR_PMAP, "pmap_enter_l2:"
" failed to replace existing mapping"