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Allow device mapping to reuse existing mapped regions when they fully overlap.

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This commit is contained in:
Martin Whitaker
2022-02-21 16:30:42 +00:00
parent e4ad2dfa1b
commit 604b22449a
1 changed files with 18 additions and 5 deletions
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23
system/vmem.c
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@@ -40,7 +40,7 @@
// Private Variables
//------------------------------------------------------------------------------
static int device_pages_used = 0;
static unsigned int device_pages_used = 0;
static uintptr_t mapped_window = 2;
@@ -76,16 +76,29 @@ static void load_pdbr()
uintptr_t map_device(uintptr_t base_addr, size_t size)
{
uintptr_t last_addr = base_addr + size - 1;
// Check if the requested region is permanently mapped.
if (last_addr < VM_WINDOW_START || (base_addr > VM_DEVICE_END && last_addr <= VM_SPACE_END)) {
return base_addr;
}
uintptr_t first_virt_page = device_pages_used;
// Check if the requested region is already mapped.
uintptr_t first_virt_page = 0;
uintptr_t first_phys_page = base_addr >> VM_PAGE_SHIFT;
uintptr_t last_phys_page = last_addr >> VM_PAGE_SHIFT;
// Compute the page table entries.
for (uintptr_t page = first_phys_page; page <= last_phys_page; page++) {
uintptr_t curr_virt_page = first_virt_page;
uintptr_t curr_phys_page = first_phys_page;
while (curr_virt_page < device_pages_used && curr_phys_page <= last_phys_page) {
uintptr_t mapped_phys_page = pd3[curr_virt_page++] >> VM_PAGE_SHIFT;
if (mapped_phys_page == curr_phys_page) {
curr_phys_page++;
} else {
first_virt_page = curr_virt_page;
curr_phys_page = first_phys_page;
}
}
// If not, map it. Note that this will extend a partial match at the end of the current map.
while (curr_phys_page <= last_phys_page) {
if (device_pages_used == MAX_DEVICE_PAGES) return 0;
pd3[device_pages_used++] = (page << VM_PAGE_SHIFT) + 0x83;
pd3[device_pages_used++] = (curr_phys_page++ << VM_PAGE_SHIFT) + 0x83;
}
// Reload the PDBR to flush any remnants of the old mapping.
load_pdbr();