Re: [PATCH v3 20/23] iommu: Update various drivers to pass in lg2sz instead of order to iommu pages

[Mostafa Saleh <smostafa@google.com>]

On Mon, Mar 17, 2025 at 10:35:00AM -0300, Jason Gunthorpe wrote:
> On Wed, Mar 12, 2025 at 12:59:00PM +0000, Mostafa Saleh wrote:
> > > --- a/drivers/iommu/io-pgtable-arm.c
> > > +++ b/drivers/iommu/io-pgtable-arm.c
> > > @@ -263,14 +263,13 @@ static void *__arm_lpae_alloc_pages(size_t size, gfp_t gfp,
> > >  				    void *cookie)
> > >  {
> > >  	struct device *dev = cfg->iommu_dev;
> > > -	int order = get_order(size);
> > >  	dma_addr_t dma;
> > >  	void *pages;
> > >  
> > >  	if (cfg->alloc)
> > >  		pages = cfg->alloc(cookie, size, gfp);
> > >  	else
> > > -		pages = iommu_alloc_pages_node(dev_to_node(dev), gfp, order);
> > > +		pages = iommu_alloc_pages_node_sz(dev_to_node(dev), gfp, size);
> > 
> > Although, the current implementation of iommu_alloc_pages_node_sz() would round
> > the size to order, but this is not correct according to the API definition
> > "The returned allocation is round_up_pow_two(size) big, and is physically aligned
> > to its size."
> 
> Yes.. The current implementation is limited to full PAGE_SIZE only,
> the documentation imagines a future where it is not. Drivers should
> ideally not assume the PAGE_SIZE limit during this conversion.
> 
> > I'd say we can align the size or use min with 64 bytes before calling the
> > function would be enough (or change the API to state that allocations
> > are rounded to order)
> 
> OK, like this:
> 
> 	if (cfg->alloc) {
> 		pages = cfg->alloc(cookie, size, gfp);
> 	} else {
> 		/*
> 		 * For very small starting-level translation tables the HW
> 		 * requires a minimum alignment of at least 64 to cover all
> 		 * cases.
> 		 */
> 		pages = iommu_alloc_pages_node_sz(dev_to_node(dev), gfp,
> 						  max(size, 64));
> 	}

Yes, that looks good.

Thanks,
Mostafa

> 
> Thanks,
> Jason