Re: [PATCH] swiotlb: check alloc_size before the allocation of a new memory pool

[zhangpeng (AS)]

On 2024/1/8 23:46, Petr Tesarik wrote:

> On 1/8/2024 3:00 PM, Peng Zhang wrote:
> > From: ZhangPeng <zhangpeng362@xxxxxxxxxx>
> >
> > The allocation request for swiotlb contiguous memory greater than
> > 128*2KB cannot be fulfilled because it exceeds the maximum contiguous
> > memory limit. If the swiotlb memory we allocate is larger than 128*2KB,
> > swiotlb_find_slots() will still schedule the allocation of a new memory
> > pool, which will increase memory overhead.
> >
> > Fix it by adding a check with alloc_size no more than 128*2KB before
> > scheduling the allocation of a new memory pool in swiotlb_find_slots().
> >
> > Signed-off-by: ZhangPeng <zhangpeng362@xxxxxxxxxx>
> > ---
> >   kernel/dma/swiotlb.c | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> > index 33d942615be5..cc92cff02c60 100644
> > --- a/kernel/dma/swiotlb.c
> > +++ b/kernel/dma/swiotlb.c
> > @@ -1126,6 +1126,9 @@ static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
> >   	u64 phys_limit;
> >   	int index;
> >   
> > +	if (alloc_size > IO_TLB_SEGSIZE * IO_TLB_SIZE)
> > +		return -1;
> > +
> >   	rcu_read_lock();
> >   	list_for_each_entry_rcu(pool, &mem->pools, node) {
> >   		index = swiotlb_pool_find_slots(dev, pool, orig_addr,
> IIUC this such big allocations are not normally required by drivers, but
> I have already run into a similar issue with a Raspberry Pi 4 dma-buf
> object, so they can be triggered at will by user space. I also believe
> this sanity check is a good idea in general, not only when dynamic
> SWIOTLB is enabled.
>
> Reviewed-by: Petr Tesarik <petr.tesarik1@xxxxxxxxxxxxxxxxxxx>
>
> Petr T

Thanks for your review!

--
Best Regards,
Peng