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Three enhancements to arm64's pmap_protect():

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Implement protection changes on superpage mappings.  Previously, a superpage
mapping was unconditionally demoted by pmap_protect(), even if the
protection change applied to the entire superpage mapping.

Precompute the bit mask describing the protection changes rather than
recomputing it for every page table entry that is changed.

Skip page table entries that already have the requested protection changes
in place.

Reviewed by:	andrew, kib
MFC after:	10 days
Differential Revision:	https://reviews.freebsd.org/D20657
This commit is contained in:
Alan Cox 2019-06-16 16:45:01 +00:00
parent b71764df96
commit bf13f9d279
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=349117
1 changed files with 72 additions and 16 deletions
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88
sys/arm64/arm64/pmap.c
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@ -2728,6 +2728,51 @@ pmap_remove_all(vm_page_t m)
vm_page_free_pages_toq(&free, true);
}
/*
* pmap_protect_l2: do the things to protect a 2MB page in a pmap
*/
static void
pmap_protect_l2(pmap_t pmap, pt_entry_t *l2, vm_offset_t sva, pt_entry_t nbits)
{
pd_entry_t old_l2;
vm_page_t m, mt;
PMAP_LOCK_ASSERT(pmap, MA_OWNED);
KASSERT((sva & L2_OFFSET) == 0,
("pmap_protect_l2: sva is not 2mpage aligned"));
old_l2 = pmap_load(l2);
KASSERT((old_l2 & ATTR_DESCR_MASK) == L2_BLOCK,
("pmap_protect_l2: L2e %lx is not a block mapping", old_l2));
/*
* Return if the L2 entry already has the desired access restrictions
* in place.
*/
if ((old_l2 | nbits) == old_l2)
return;
/*
* When a dirty read/write superpage mapping is write protected,
* update the dirty field of each of the superpage's constituent 4KB
* pages.
*/
if ((nbits & ATTR_AP(ATTR_AP_RO)) != 0 &&
(old_l2 & ATTR_SW_MANAGED) != 0 &&
pmap_page_dirty(old_l2)) {
m = PHYS_TO_VM_PAGE(old_l2 & ~ATTR_MASK);
for (mt = m; mt < &m[L2_SIZE / PAGE_SIZE]; mt++)
vm_page_dirty(mt);
}
pmap_set(l2, nbits);
/*
* Since a promotion must break the 4KB page mappings before making
* the 2MB page mapping, a pmap_invalidate_page() suffices.
*/
pmap_invalidate_page(pmap, sva);
}
/*
* Set the physical protection on the
* specified range of this map as requested.
@ -2745,8 +2790,12 @@ pmap_protect(pmap_t pmap, vm_offset_t sva, vm_offset_t eva, vm_prot_t prot)
return;
}
if ((prot & (VM_PROT_WRITE | VM_PROT_EXECUTE)) ==
(VM_PROT_WRITE | VM_PROT_EXECUTE))
nbits = 0;
if ((prot & VM_PROT_WRITE) == 0)
nbits |= ATTR_AP(ATTR_AP_RO);
if ((prot & VM_PROT_EXECUTE) == 0)
nbits |= ATTR_XN;
if (nbits == 0)
return;
PMAP_LOCK(pmap);
@ -2777,8 +2826,10 @@ pmap_protect(pmap_t pmap, vm_offset_t sva, vm_offset_t eva, vm_prot_t prot)
continue;
if ((pmap_load(l2) & ATTR_DESCR_MASK) == L2_BLOCK) {
l3p = pmap_demote_l2(pmap, l2, sva);
if (l3p == NULL)
if (sva + L2_SIZE == va_next && eva >= va_next) {
pmap_protect_l2(pmap, l2, sva, nbits);
continue;
} else if (pmap_demote_l2(pmap, l2, sva) == NULL)
continue;
}
KASSERT((pmap_load(l2) & ATTR_DESCR_MASK) == L2_TABLE,
@ -2790,8 +2841,16 @@ pmap_protect(pmap_t pmap, vm_offset_t sva, vm_offset_t eva, vm_prot_t prot)
va = va_next;
for (l3p = pmap_l2_to_l3(l2, sva); sva != va_next; l3p++,
sva += L3_SIZE) {
/*
* Go to the next L3 entry if the current one is
* invalid or already has the desired access
* restrictions in place. (The latter case occurs
* frequently. For example, in a "buildworld"
* workload, almost 1 out of 4 L3 entries already
* have the desired restrictions.)
*/
l3 = pmap_load(l3p);
if (!pmap_l3_valid(l3)) {
if (!pmap_l3_valid(l3) || (l3 | nbits) == l3) {
if (va != va_next) {
pmap_invalidate_range(pmap, va, sva);
va = va_next;
@ -2801,17 +2860,14 @@ pmap_protect(pmap_t pmap, vm_offset_t sva, vm_offset_t eva, vm_prot_t prot)
if (va == va_next)
va = sva;
nbits = 0;
if ((prot & VM_PROT_WRITE) == 0) {
if ((l3 & ATTR_SW_MANAGED) &&
pmap_page_dirty(l3)) {
vm_page_dirty(PHYS_TO_VM_PAGE(l3 &
~ATTR_MASK));
}
nbits |= ATTR_AP(ATTR_AP_RO);
}
if ((prot & VM_PROT_EXECUTE) == 0)
nbits |= ATTR_XN;
/*
* When a dirty read/write mapping is write protected,
* update the page's dirty field.
*/
if ((nbits & ATTR_AP(ATTR_AP_RO)) != 0 &&
(l3 & ATTR_SW_MANAGED) != 0 &&
pmap_page_dirty(l3))
vm_page_dirty(PHYS_TO_VM_PAGE(l3 & ~ATTR_MASK));
pmap_set(l3p, nbits);
}