On 7/2/25 12:28 PM, Jan Beulich wrote:
On 02.07.2025 12:09, Jan Beulich wrote:
On 10.06.2025 15:05, Oleksii Kurochko wrote:
@@ -613,3 +612,91 @@ void __iomem *ioremap(paddr_t pa, size_t len)
{
return ioremap_attr(pa, len, PAGE_HYPERVISOR_NOCACHE);
}
+
+int page_is_ram_type(unsigned long mfn, unsigned long mem_type)
+{
+ ASSERT_UNREACHABLE();
+
+ return 0;
+}
+
+static struct domain *page_get_owner_and_nr_reference(struct page_info *page,
+ unsigned long nr)
+{
+ unsigned long x, y = page->count_info;
+ struct domain *owner;
+
+ /* Restrict nr to avoid "double" overflow */
+ if ( nr >= PGC_count_mask )
+ {
+ ASSERT_UNREACHABLE();
+ return NULL;
+ }
I question the validity of this, already in the Arm original: I can't spot
how the caller guarantees to stay below that limit. Without such an
(attempted) guarantee, ASSERT_UNREACHABLE() is wrong to use. All I can see
is process_shm_node() incrementing shmem_extra[].nr_shm_borrowers, without
any limit check.
+ do {
+ x = y;
+ /*
+ * Count == 0: Page is not allocated, so we cannot take a reference.
+ * Count == -1: Reference count would wrap, which is invalid.
+ */
May I once again ask that you look carefully at comments (as much as at code)
you copy. Clearly this comment wasn't properly updated when the bumping by 1
was changed to bumping by nr.
+ if ( unlikely(((x + nr) & PGC_count_mask) <= nr) )
+ return NULL;
+ }
+ while ( (y = cmpxchg(&page->count_info, x, x + nr)) != x );
+
+ owner = page_get_owner(page);
+ ASSERT(owner);
+
+ return owner;
+}
There also looks to be a dead code concern here (towards the "nr" parameters
here and elsewhere, when STATIC_SHM=n). Just that apparently we decided to
leave out Misra rule 2.2 entirely.
I think that I didn't get what is an issue when STATIC_SHM=n, functions is still
going to be called through page_get_owner_and_reference(), at least, in
page_alloc.c .
~ Oleksii
