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kernel/vm: Areas without source caches need commitments for READ protections.

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May fix #19678.
This commit is contained in:
Augustin Cavalier
2025-07-12 14:27:13 -04:00
parent 6bb82d2942
commit 3978032551
1 changed files with 32 additions and 24 deletions
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src/system/kernel/vm/vm.cpp
+32 -24
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@@ -594,11 +594,15 @@ get_area_page_protection(VMArea* area, addr_t pageAddress)
/*! Computes the committed size an area's cache ought to have,
based on the area's page_protections and any pages already present.
*/
static inline uint32
static inline size_t
compute_area_page_commitment(VMArea* area)
{
uint32 commitProtection = B_WRITE_AREA | B_KERNEL_WRITE_AREA;
if (area->cache->source == NULL)
commitProtection |= B_READ_AREA | B_KERNEL_READ_AREA;
if (area->page_protections == NULL) {
if ((area->protection & (B_WRITE_AREA | B_KERNEL_WRITE_AREA)) != 0)
if ((area->protection & commitProtection) != 0)
return area->Size();
return area->cache->page_count * B_PAGE_SIZE;
}
@@ -612,7 +616,7 @@ compute_area_page_commitment(VMArea* area)
if (area->cache->LookupPage(pageOffset) != NULL)
pages++;
else
pages += ((protection & (B_WRITE_AREA << 0)) != 0) ? 1 : 0;
pages += ((protection & (commitProtection << 0)) != 0) ? 1 : 0;
if (i == (bytes - 1) && oddPageCount)
break;
@@ -620,7 +624,7 @@ compute_area_page_commitment(VMArea* area)
if (area->cache->LookupPage(pageOffset + B_PAGE_SIZE) != NULL)
pages++;
else
pages += ((protection & (B_WRITE_AREA << 4)) != 0) ? 1 : 0;
pages += ((protection & (commitProtection << 4)) != 0) ? 1 : 0;
}
return pages;
}
@@ -1260,8 +1264,16 @@ map_backing_store(VMAddressSpace* addressSpace, VMCache* cache, off_t offset,
cache = newCache;
}
// attach the cache to the area
area->cache = cache;
area->cache_offset = offset;
// point the cache back to the area
cache->InsertAreaLocked(area);
if ((flags & CREATE_AREA_DONT_COMMIT_MEMORY) == 0) {
status = cache->SetMinimalCommitment(size, priority);
const size_t commitmentPages = compute_area_page_commitment(area);
status = cache->SetMinimalCommitment(commitmentPages * B_PAGE_SIZE, priority);
if (status != B_OK)
goto err2;
}
@@ -1298,12 +1310,6 @@ map_backing_store(VMAddressSpace* addressSpace, VMCache* cache, off_t offset,
if (status != B_OK)
goto err2;
// attach the cache to the area
area->cache = cache;
area->cache_offset = offset;
// point the cache back to the area
cache->InsertAreaLocked(area);
if (mapping == REGION_PRIVATE_MAP)
cache->Unlock();
@@ -1323,9 +1329,13 @@ map_backing_store(VMAddressSpace* addressSpace, VMCache* cache, off_t offset,
err3:
cache->Lock();
cache->RemoveArea(area);
area->cache = NULL;
addressSpace->RemoveArea(area, allocationFlags);
err2:
cache->Unlock();
cache->RemoveArea(area);
cache->Lock();
area->cache = NULL;
if (mapping == REGION_PRIVATE_MAP) {
// We created this cache, so we must delete it again. Note, that we
// need to temporarily unlock the source cache or we'll otherwise
@@ -2313,12 +2323,6 @@ _vm_map_file(team_id team, const char* name, void** _address,
uint32 mappingFlags = 0;
if (unmapAddressRange)
mappingFlags |= CREATE_AREA_UNMAP_ADDRESS_RANGE;
if (mapping == REGION_PRIVATE_MAP) {
// For privately mapped read-only regions, skip committing memory.
// (If protections are changed later on, memory will be committed then.)
if ((protection & (B_WRITE_AREA | B_KERNEL_WRITE_AREA)) == 0)
mappingFlags |= CREATE_AREA_DONT_COMMIT_MEMORY;
}
if (fd < 0) {
virtual_address_restrictions virtualRestrictions = {};
@@ -6430,7 +6434,11 @@ _user_set_memory_protection(void* _address, size_t size, uint32 protection)
// Adjust the committed size, if necessary.
if (is_area_only_cache_user(area) && !topCache->CanOvercommit()) {
const bool becomesWritable = (protection & B_WRITE_AREA) != 0;
uint8 commitProtection = B_WRITE_AREA;
if (topCache->source == NULL)
commitProtection |= B_READ_AREA;
const bool newNeedsCommitment = (protection & commitProtection) != 0;
ssize_t commitmentChange = 0;
const off_t areaCacheBase = area->Base() - area->cache_offset;
for (addr_t pageAddress = area->Base() + offset;
@@ -6440,12 +6448,12 @@ _user_set_memory_protection(void* _address, size_t size, uint32 protection)
continue;
}
const bool isWritable
= (get_area_page_protection(area, pageAddress) & B_WRITE_AREA) != 0;
const bool nowNeedsCommitment
= (get_area_page_protection(area, pageAddress) & commitProtection) != 0;
if (becomesWritable && !isWritable)
if (newNeedsCommitment && !nowNeedsCommitment)
commitmentChange += B_PAGE_SIZE;
else if (!becomesWritable && isWritable)
else if (!newNeedsCommitment && nowNeedsCommitment)
commitmentChange -= B_PAGE_SIZE;
}