[PATCH v4 1/3] x86/vmemmap: Drop handling of 4K unaligned vmemmap range

Oscar Salvador
2021-03-01T08:35:24Z

remove_pte_table() is prepared to handle the case where either the
start or the end of the range is not PAGE aligned.
This cannot actually happen:

__populate_section_memmap enforces the range to be PMD aligned,
so as long as the size of the struct page remains multiple of 8,
the vmemmap range will be aligned to PAGE_SIZE.

Drop the dead code and place a VM_BUG_ON in vmemmap_{populate,free}
to catch nasty cases.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
Suggested-by: David Hildenbrand <david@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
---
arch/x86/mm/init_64.c | 48 +++++++++++++-----------------------------------
1 file changed, 13 insertions(+), 35 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index b5a3fa4033d3..b0e1d215c83e 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -962,7 +962,6 @@ remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end,
{
unsigned long next, pages = 0;
pte_t *pte;
- void *page_addr;
phys_addr_t phys_addr;

pte = pte_start + pte_index(addr);
@@ -983,42 +982,15 @@ remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end,
if (phys_addr < (phys_addr_t)0x40000000)
return;

- if (PAGE_ALIGNED(addr) && PAGE_ALIGNED(next)) {
- /*
- * Do not free direct mapping pages since they were
- * freed when offlining, or simplely not in use.
- */
- if (!direct)
- free_pagetable(pte_page(*pte), 0);
-
- spin_lock(&init_mm.page_table_lock);
- pte_clear(&init_mm, addr, pte);
- spin_unlock(&init_mm.page_table_lock);
+ if (!direct)
+ free_pagetable(pte_page(*pte), 0);

- /* For non-direct mapping, pages means nothing. */
- pages++;
- } else {
- /*
- * If we are here, we are freeing vmemmap pages since
- * direct mapped memory ranges to be freed are aligned.
- *
- * If we are not removing the whole page, it means
- * other page structs in this page are being used and
- * we canot remove them. So fill the unused page_structs
- * with 0xFD, and remove the page when it is wholly
- * filled with 0xFD.
- */
- memset((void *)addr, PAGE_INUSE, next - addr);
-
- page_addr = page_address(pte_page(*pte));
- if (!memchr_inv(page_addr, PAGE_INUSE, PAGE_SIZE)) {
- free_pagetable(pte_page(*pte), 0);
+ spin_lock(&init_mm.page_table_lock);
+ pte_clear(&init_mm, addr, pte);
+ spin_unlock(&init_mm.page_table_lock);

- spin_lock(&init_mm.page_table_lock);
- pte_clear(&init_mm, addr, pte);
- spin_unlock(&init_mm.page_table_lock);
- }
- }
+ /* For non-direct mapping, pages means nothing. */
+ pages++;
}

/* Call free_pte_table() in remove_pmd_table(). */
@@ -1197,6 +1169,9 @@ remove_pagetable(unsigned long start, unsigned long end, bool direct,
void __ref vmemmap_free(unsigned long start, unsigned long end,
struct vmem_altmap *altmap)
{
+ VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE));
+ VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));
+
remove_pagetable(start, end, false, altmap);
}

@@ -1556,6 +1531,9 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
{
int err;

+ VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE));
+ VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));
+
if (end - start < PAGES_PER_SECTION * sizeof(struct page))
err = vmemmap_populate_basepages(start, end, node, NULL);
else if (boot_cpu_has(X86_FEATURE_PSE))
--
2.16.3