From 1f89036816a1a3d45e62b101a9cff873ac41dfbc Mon Sep 17 00:00:00 2001 From: Ian McFarlane Date: Fri, 25 Apr 2025 10:24:35 -0400 Subject: fix freeing of virtual memory --- kernel/memory/paging.c | 57 +++++++++++++++++++++++++++++++++++--------------- 1 file changed, 40 insertions(+), 17 deletions(-) (limited to 'kernel/memory/paging.c') diff --git a/kernel/memory/paging.c b/kernel/memory/paging.c index c6e6a82..8de1a24 100644 --- a/kernel/memory/paging.c +++ b/kernel/memory/paging.c @@ -804,36 +804,59 @@ void *mem_alloc_pages_at(mem_ctx_t ctx, size_t count, void *virt, unsigned int flags) { size_t pages_needed = count; - uint8_t *virtual_address = virt; - void *phys_start = NULL; + struct phys_page_slice prev_phys_block = PHYS_PAGE_SLICE_NULL; + struct phys_page_slice phys_pages; while (pages_needed > 0) { - struct phys_page_slice phys_pages = - alloc_phys_page_withextra(pages_needed); + phys_pages = alloc_phys_page_withextra(pages_needed); if (phys_pages.pagestart == NULL) { - free_phys_pages(phys_start ? phys_start : phys_pages.pagestart, - count - pages_needed); - return NULL; + goto mem_alloc_pages_at_fail; } - if (!phys_start) - phys_start = phys_pages.pagestart; + { + // allocate the first page and store in it the physical address of the + // previous chunk of pages + // TODO: skip this if there are already enough pages from first alloc + void *pageone = kmapaddr(phys_pages.pagestart, NULL, 1, + F_PRESENT | F_WRITEABLE); + if (pageone == NULL) { + panic("kernel out of virtual memory"); + } + *((struct phys_page_slice *)pageone) = prev_phys_block; + prev_phys_block = phys_pages; + kunmapaddr(pageone); + } assert(pages_needed >= phys_pages.num_pages, "overflow"); pages_needed -= phys_pages.num_pages; - virtual_address += phys_pages.num_pages * PAGE_SIZE; - - if (map_pages((volatile struct pml4 *)ctx->pml4, - (void *)virtual_address, phys_pages.pagestart, flags, - phys_pages.num_pages)) { - assert(phys_start, "expected something allocated"); - free_phys_pages(phys_start, count - pages_needed); - return NULL; + + // index into virtual page array at index [count - pages_needed] + void *vaddr = ((uint8_t *)virt) + ((count - pages_needed) * PAGE_SIZE); + if (map_pages((volatile struct pml4 *)ctx->pml4, vaddr, + phys_pages.pagestart, flags, phys_pages.num_pages)) { + goto mem_alloc_pages_at_fail; } } return virt; + +mem_alloc_pages_at_fail: + while (prev_phys_block.pagestart) { + void *virtpage = kmapaddr(prev_phys_block.pagestart, NULL, 1, + F_PRESENT | F_WRITEABLE); + if (!virtpage) { + // memory corruption, most likely a bug + // could also ERROR here and exit with leak + panic("unable to free memory from failed mem_alloc_pages_at call"); + } + struct phys_page_slice prev = *(struct phys_page_slice *)virtpage; + prev_phys_block = prev; + free_phys_pages_slice(prev); + kunmapaddr(virtpage); + } + + return NULL; } void mem_free_pages(mem_ctx_t ctx, const void *virt) -- cgit v1.2.3-freya