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x86/mm: Always "broadcast" PMD setting operations

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Kernel PMDs can either be shared across processes or private to a
process.  On 64-bit, they are always shared.  32-bit non-PAE hardware
does not have PMDs, but the kernel logically squishes them into the
PGD and treats them as private. Here are the four cases:

	64-bit:                Shared
	32-bit: non-PAE:       Private
	32-bit:     PAE+  PTI: Private
	32-bit:     PAE+noPTI: Shared

Note that 32-bit is all "Private" except for PAE+noPTI being an
oddball.  The 32-bit+PAE+noPTI case will be made like the rest of
32-bit shortly.

But until that can be done, temporarily treat the 32-bit+PAE+noPTI
case as Private. This will do unnecessary walks across pgd_list and
unnecessary PTE setting but should be otherwise harmless.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20250414173235.F63F50D1%40davehans-spike.ostc.intel.com
This commit is contained in:
Dave Hansen 2025-04-14 10:32:35 -07:00
parent 780f97e309
commit b0cc4d19f1
2 changed files with 5 additions and 10 deletions
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4
arch/x86/mm/pat/set_memory.c
View File

@ -889,7 +889,7 @@ static void __set_pmd_pte(pte_t *kpte, unsigned long address, pte_t pte)
/* change init_mm */
set_pte_atomic(kpte, pte);
#ifdef CONFIG_X86_32
if (!SHARED_KERNEL_PMD) {
{
struct page *page;
list_for_each_entry(page, &pgd_list, lru) {
@ -1293,7 +1293,7 @@ static int collapse_pmd_page(pmd_t *pmd, unsigned long addr,
/* Queue the page table to be freed after TLB flush */
list_add(&page_ptdesc(pmd_page(old_pmd))->pt_list, pgtables);
if (IS_ENABLED(CONFIG_X86_32) && !SHARED_KERNEL_PMD) {
if (IS_ENABLED(CONFIG_X86_32)) {
struct page *page;
/* Update all PGD tables to use the same large page */

11
arch/x86/mm/pgtable.c
View File

@ -97,18 +97,13 @@ static void pgd_ctor(struct mm_struct *mm, pgd_t *pgd)
KERNEL_PGD_PTRS);
}
/* list required to sync kernel mapping updates */
if (!SHARED_KERNEL_PMD) {
pgd_set_mm(pgd, mm);
pgd_list_add(pgd);
}
/* List used to sync kernel mapping updates */
pgd_set_mm(pgd, mm);
pgd_list_add(pgd);
}
static void pgd_dtor(pgd_t *pgd)
{
if (SHARED_KERNEL_PMD)
return;
spin_lock(&pgd_lock);
pgd_list_del(pgd);
spin_unlock(&pgd_lock);