On 4 Dec 2024, at 11:29, Matthew Wilcox wrote:
> On Wed, Dec 04, 2024 at 11:16:51AM -0500, Zi Yan wrote:
>>> So maybe the clearing done as part of page allocator isn't enough here.
>>>
>> Basically, mips needs to flush data cache if kmap address is aliased to
>
> People use "aliased" in contronym ways. Do you mean "has a
> non-congruent alias" or "has a congruent alias"?
I mean if kmap address goes into a different cache line than userspace
address, a cache flush is needed to make sure data is visible to
userspace.
>
>> userspace address. This means when mips has THP on, the patch below
>> is not enough to fix the issue.
>>
>> In post_alloc_hook(), it does not make sense to pass userspace address
>> in to determine whether to flush dcache or not.
>>
>> One way to fix it is to add something like arch_userpage_post_alloc()
>> to flush dcache if kmap address is aliased to userspace address.
>> But my questions are that
>> 1) if kmap address will always be the same for two separate kmap_local() calls,
>
> No. It just takes the next address in the stack.
So this fix will not work, since it is possible that first kmap and second
kmap have different pages_do_alias() return values.
Another way would be to make a special case for mips, like below.
But that looks ugly, let me think about it more.
diff --git a/arch/mips/include/asm/page.h b/arch/mips/include/asm/page.h
index bc3e3484c1bf..ef3c6f0b9159 100644
--- a/arch/mips/include/asm/page.h
+++ b/arch/mips/include/asm/page.h
@@ -95,6 +95,19 @@ struct vm_area_struct;
extern void copy_user_highpage(struct page *to, struct page *from,
unsigned long vaddr, struct vm_area_struct *vma);
+struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
+ unsigned long vaddr)
+ {
+ struct folio *folio;
+
+ folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr);
+ if (folio)
+ clear_user_highpage(&folio->page, vaddr);
+
+ return folio;
+ }
+#define vma_alloc_zeroed_movable_folio vma_alloc_zeroed_movable_folio
+
#define __HAVE_ARCH_COPY_USER_HIGHPAGE
/*
diff --git a/mm/internal.h b/mm/internal.h
index cb8d8e8e3ffa..d513fa683aa3 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1287,7 +1287,8 @@ void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
static inline bool alloc_zeroed(void)
{
- return static_branch_maybe(CONFIG_INIT_ON_ALLOC_DEFAULT_ON,
+ return !IS_ENABLED(CONFIG_MIPS) &&
+ static_branch_maybe(CONFIG_INIT_ON_ALLOC_DEFAULT_ON,
&init_on_alloc);
}
Best Regards,
Yan, Zi
