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amd64: Add comments to pmap_pinit_type()

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... explaining why we don't pass the pmap pointer to
pmap_alloc_pt_page().

Reported by:	alc
Reviewed by:	alc, kib
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D32528
This commit is contained in:
Mark Johnston 2021-10-19 20:29:18 -04:00
parent ff93447d8e
commit 34fac29e98
1 changed files with 7 additions and 1 deletions
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8
sys/amd64/amd64/pmap.c
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@ -4345,7 +4345,9 @@ pmap_pinit_type(pmap_t pmap, enum pmap_type pm_type, int flags)
int i;
/*
* allocate the page directory page
* Allocate the page directory page. Pass NULL instead of a pointer to
* the pmap here to avoid recording this page in the resident count, as
* optimizations in pmap_remove() depend on this.
*/
pmltop_pg = pmap_alloc_pt_page(NULL, 0, VM_ALLOC_WIRED | VM_ALLOC_ZERO |
VM_ALLOC_WAITOK);
@ -4377,6 +4379,10 @@ pmap_pinit_type(pmap_t pmap, enum pmap_type pm_type, int flags)
else
pmap_pinit_pml4(pmltop_pg);
if ((curproc->p_md.md_flags & P_MD_KPTI) != 0) {
/*
* As with pmltop_pg, pass NULL instead of a pointer to
* the pmap to ensure that the PTI page isn't counted.
*/
pmltop_pgu = pmap_alloc_pt_page(NULL, 0,
VM_ALLOC_WIRED | VM_ALLOC_WAITOK);
pmap->pm_pmltopu = (pml4_entry_t *)PHYS_TO_DMAP(