Re: [PATCH v3 1/1] iommu/sva: Invalidate KVA range on kernel TLB flush

[Baolu Lu <baolu.lu@linux.intel.com>]

On 8/26/2025 10:22 PM, Dave Hansen wrote:
> On 8/25/25 19:49, Baolu Lu wrote:
>>> The three separate lists are needed because we're handling three
>>> distinct types of page deallocation. Grouping the pages this way allows
>>> the workqueue handler to free each type using the correct function.
>>
>> Please allow me to add more details.
> 
> Right, I know why it got added this way: it was the quickest way to hack
> together a patch that fixes the IOMMU issue without refactoring anything.
> 
> I agree that you have three cases:
> 1. A full on 'struct ptdesc' that needs its destructor run
> 2. An order-0 'struct page'
> 3. A higher-order 'struct page'
> 
> Long-term, #2 and #3 probably need to get converted over to 'struct
> ptdesc'. They don't look _that_ hard to convert to me. Willy, Vishal,
> any other mm folks: do you agree?
> 
> Short-term, I'd just consolidate your issue down to a single list.
> 
> #1: For 'struct ptdesc', modify pte_free_kernel() to pass information in
>      to pagetable_dtor_free() to tell it to use the deferred page table
>      free list. Do this with a bit in the ptdesc or a new argument to
>      pagetable_dtor_free().
> #2. Just append these to the deferred page table free list. Easy.
> #3. The biggest hacky way to do this is to just treat the higher-order
>      non-compound page and put the pages on the deferred page table
>      free list one at a time. The other way to do it is to track down how
>      this thing got allocated in the first place and make sure it's got
>      __GFP_COMP metadata. If so, you can just use __free_pages() for
>      everything.
> 
> Yeah, it'll take a couple patches up front to refactor some things. But
> that refactoring will make things more consistent instead of adding
> adding complexity to deal with the inconsistency.

Following the insights above, I wrote the code as follows. Does it look
good?

mm/pgtable-generic.c:

#ifdef CONFIG_ASYNC_PGTABLE_FREE
/* a 'struct ptdesc' that needs its destructor run */
#define ASYNC_PGTABLE_FREE_DTOR	BIT(NR_PAGEFLAGS)

static void kernel_pgtable_work_func(struct work_struct *work);

static struct {
	struct list_head list;
	/* protect above ptdesc lists */
	spinlock_t lock;
	struct work_struct work;
} kernel_pgtable_work = {
	.list = LIST_HEAD_INIT(kernel_pgtable_work.list),
	.lock = __SPIN_LOCK_UNLOCKED(kernel_pgtable_work.lock),
	.work = __WORK_INITIALIZER(kernel_pgtable_work.work, 
kernel_pgtable_work_func),
};

static void kernel_pgtable_work_func(struct work_struct *work)
{
	struct ptdesc *ptdesc, *next;
	LIST_HEAD(page_list);

	spin_lock(&kernel_pgtable_work.lock);
	list_splice_tail_init(&kernel_pgtable_work.list, &page_list);
	spin_unlock(&kernel_pgtable_work.lock);

	iommu_sva_invalidate_kva_range(0, TLB_FLUSH_ALL);

	list_for_each_entry_safe(ptdesc, next, &page_list, pt_list) {
		list_del(&ptdesc->pt_list);
		if (ptdesc->__page_flags & ASYNC_PGTABLE_FREE_DTOR)
			pagetable_dtor_free(ptdesc);
		else
			__free_page(ptdesc_page(ptdesc));
	}
}

void kernel_pgtable_async_free_dtor(struct ptdesc *ptdesc)
{
	spin_lock(&kernel_pgtable_work.lock);
	ptdesc->__page_flags |= ASYNC_PGTABLE_FREE_DTOR;
	list_add(&ptdesc->pt_list, &kernel_pgtable_work.list);
	spin_unlock(&kernel_pgtable_work.lock);

	schedule_work(&kernel_pgtable_work.work);
}

void kernel_pgtable_async_free_page_list(struct list_head *list)
{
	spin_lock(&kernel_pgtable_work.lock);
	list_splice_tail(list, &kernel_pgtable_work.list);
	spin_unlock(&kernel_pgtable_work.lock);

	schedule_work(&kernel_pgtable_work.work);
}

void kernel_pgtable_async_free_page(struct page *page)
{
	spin_lock(&kernel_pgtable_work.lock);
	list_add(&page_ptdesc(page)->pt_list, &kernel_pgtable_work.list);
	spin_unlock(&kernel_pgtable_work.lock);

	schedule_work(&kernel_pgtable_work.work);
}
#endif

Thanks,
baolu