mm/kasan: avoid lazy MMU mode hazards

Functions __kasan_populate_vmalloc() and __kasan_depopulate_vmalloc() use
apply_to_pte_range(), which enters lazy MMU mode.  In that mode updating
PTEs may not be observed until the mode is left.

That may lead to a situation in which otherwise correct reads and writes
to a PTE using ptep_get(), set_pte(), pte_clear() and other access
primitives bring wrong results when the vmalloc shadow memory is being
(de-)populated.

To avoid these hazards leave the lazy MMU mode before and re-enter it
after each PTE manipulation.

Link: https://lkml.kernel.org/r/0d2efb7ddddbff6b288fbffeeb10166e90771718.1755528662.git.agordeev@linux.ibm.com
Fixes: 3c5c3cf ("kasan: support backing vmalloc space with real shadow memory")
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Alexander Gordeev

mm/kasan/shadow.c

@@ -305,6 +305,8 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
 	pte_t pte;
 	int index;
 
+	arch_leave_lazy_mmu_mode();
+
 	index = PFN_DOWN(addr - data->start);
 	page = data->pages[index];
 	__memset(page_to_virt(page), KASAN_VMALLOC_INVALID, PAGE_SIZE);
@@ -317,6 +319,8 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
 	}
 	spin_unlock(&init_mm.page_table_lock);
 
+	arch_enter_lazy_mmu_mode();
+
 	return 0;
 }
 
@@ -461,6 +465,8 @@ static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
 	pte_t pte;
 	int none;
 
+	arch_leave_lazy_mmu_mode();
+
 	spin_lock(&init_mm.page_table_lock);
 	pte = ptep_get(ptep);
 	none = pte_none(pte);
@@ -471,6 +477,8 @@ static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
 	if (likely(!none))
 		__free_page(pfn_to_page(pte_pfn(pte)));
 
+	arch_enter_lazy_mmu_mode();
+
 	return 0;
 }