linux-kernel - Re: [PATCH v1 02/10] powerpc/kernel/iommu: Align size for IOMMU_PAGE_SIZE on iommu_*

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Message-ID: <7b9640e0-568f-1470-40f4-a3ccec8abcf2@ozlabs.ru>
Date:   Sat, 22 Aug 2020 20:07:00 +1000
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Leonardo Bras <leobras.c@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Christophe Leroy <christophe.leroy@....fr>,
        Joel Stanley <joel@....id.au>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Ram Pai <linuxram@...ibm.com>,
        Brian King <brking@...ux.vnet.ibm.com>,
        Murilo Fossa Vicentini <muvic@...ux.ibm.com>,
        David Dai <zdai@...ux.vnet.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 02/10] powerpc/kernel/iommu: Align size for
 IOMMU_PAGE_SIZE on iommu_*_coherent()



On 18/08/2020 09:40, Leonardo Bras wrote:
> Both iommu_alloc_coherent() and iommu_free_coherent() assume that once
> size is aligned to PAGE_SIZE it will be aligned to IOMMU_PAGE_SIZE.

The only case when it is not aligned is when IOMMU_PAGE_SIZE > PAGE_SIZE
which is unlikely but not impossible, we could configure the kernel for
4K system pages and 64K IOMMU pages I suppose. Do we really want to do
this here, or simply put WARN_ON(tbl->it_page_shift > PAGE_SHIFT)?
Because if we want the former (==support), then we'll have to align the
size up to the bigger page size when allocating/zeroing system pages,
etc. Bigger pages are not the case here as I understand it.


> 
> Update those functions to guarantee alignment with requested size
> using IOMMU_PAGE_ALIGN() before doing iommu_alloc() / iommu_free().
> 
> Also, on iommu_range_alloc(), replace ALIGN(n, 1 << tbl->it_page_shift)
> with IOMMU_PAGE_ALIGN(n, tbl), which seems easier to read.
> 
> Signed-off-by: Leonardo Bras <leobras.c@...il.com>
> ---
>  arch/powerpc/kernel/iommu.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
> index 9704f3f76e63..d7086087830f 100644
> --- a/arch/powerpc/kernel/iommu.c
> +++ b/arch/powerpc/kernel/iommu.c
> @@ -237,10 +237,9 @@ static unsigned long iommu_range_alloc(struct device *dev,
>  	}
>  
>  	if (dev)
> -		boundary_size = ALIGN(dma_get_seg_boundary(dev) + 1,
> -				      1 << tbl->it_page_shift);
> +		boundary_size = IOMMU_PAGE_ALIGN(dma_get_seg_boundary(dev) + 1, tbl);


Run checkpatch.pl, should complain about a long line.


>  	else
> -		boundary_size = ALIGN(1UL << 32, 1 << tbl->it_page_shift);
> +		boundary_size = IOMMU_PAGE_ALIGN(1UL << 32, tbl);
>  	/* 4GB boundary for iseries_hv_alloc and iseries_hv_map */
>  
>  	n = iommu_area_alloc(tbl->it_map, limit, start, npages, tbl->it_offset,
> @@ -858,6 +857,7 @@ void *iommu_alloc_coherent(struct device *dev, struct iommu_table *tbl,
>  	unsigned int order;
>  	unsigned int nio_pages, io_order;
>  	struct page *page;
> +	size_t size_io = size;
>  
>  	size = PAGE_ALIGN(size);
>  	order = get_order(size);
> @@ -884,8 +884,9 @@ void *iommu_alloc_coherent(struct device *dev, struct iommu_table *tbl,
>  	memset(ret, 0, size);
>  
>  	/* Set up tces to cover the allocated range */
> -	nio_pages = size >> tbl->it_page_shift;
> -	io_order = get_iommu_order(size, tbl);
> +	size_io = IOMMU_PAGE_ALIGN(size_io, tbl);
> +	nio_pages = size_io >> tbl->it_page_shift;
> +	io_order = get_iommu_order(size_io, tbl);
>  	mapping = iommu_alloc(dev, tbl, ret, nio_pages, DMA_BIDIRECTIONAL,
>  			      mask >> tbl->it_page_shift, io_order, 0);
>  	if (mapping == DMA_MAPPING_ERROR) {
> @@ -900,11 +901,11 @@ void iommu_free_coherent(struct iommu_table *tbl, size_t size,
>  			 void *vaddr, dma_addr_t dma_handle)
>  {
>  	if (tbl) {
> -		unsigned int nio_pages;
> +		size_t size_io = IOMMU_PAGE_ALIGN(size, tbl);
> +		unsigned int nio_pages = size_io >> tbl->it_page_shift;
>  
> -		size = PAGE_ALIGN(size);
> -		nio_pages = size >> tbl->it_page_shift;
>  		iommu_free(tbl, dma_handle, nio_pages);
> +

Unrelated new line.


>  		size = PAGE_ALIGN(size);
>  		free_pages((unsigned long)vaddr, get_order(size));
>  	}
> 

-- 
Alexey