Re: [PATCH 09/10] xen/arm: introduce phys/dma translations in xen_dma_sync_for_*

[Julien Grall <julien@xxxxxxx>]

Hi,

On 21/05/2020 00:45, Stefano Stabellini wrote:
> From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
>
> Add phys_to_dma/dma_to_phys calls to
> xen_dma_sync_for_cpu, xen_dma_sync_for_device, and
> xen_arch_need_swiotlb.
>
> In xen_arch_need_swiotlb, take the opportunity to switch to the simpler
> pfn_valid check we use everywhere else.
>
> dma_cache_maint is fixed by the next patch.
Like patch #8, this explains what the code is doing not why this is 
necessary.
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
> ---
>   arch/arm/xen/mm.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
> index f2414ea40a79..7639251bcc79 100644
> --- a/arch/arm/xen/mm.c
> +++ b/arch/arm/xen/mm.c
> @@ -1,5 +1,6 @@
>   // SPDX-License-Identifier: GPL-2.0-only
>   #include <linux/cpu.h>
> +#include <linux/dma-direct.h>
>   #include <linux/dma-noncoherent.h>
>   #include <linux/gfp.h>
>   #include <linux/highmem.h>
> @@ -75,7 +76,7 @@ void xen_dma_sync_for_cpu(struct device *dev, dma_addr_t 
> handle,
>                           phys_addr_t paddr, size_t size,
>                           enum dma_data_direction dir)
>   {
> -       if (pfn_valid(PFN_DOWN(handle)))
> +       if (pfn_valid(PFN_DOWN(dma_to_phys(dev, handle))))
>                 arch_sync_dma_for_cpu(paddr, size, dir);
>         else if (dir != DMA_TO_DEVICE)
>                 dma_cache_maint(handle, size, GNTTAB_CACHE_INVAL);
> @@ -85,7 +86,7 @@ void xen_dma_sync_for_device(struct device *dev, dma_addr_t 
> handle,
>                              phys_addr_t paddr, size_t size,
>                              enum dma_data_direction dir)
>   {
> -       if (pfn_valid(PFN_DOWN(handle)))
> +       if (pfn_valid(PFN_DOWN(dma_to_phys(dev, handle))))
>                 arch_sync_dma_for_device(paddr, size, dir);
>         else if (dir == DMA_FROM_DEVICE)
>                 dma_cache_maint(handle, size, GNTTAB_CACHE_INVAL);
> @@ -97,8 +98,7 @@ bool xen_arch_need_swiotlb(struct device *dev,
>                            phys_addr_t phys,
>                            dma_addr_t dev_addr)
>   {
> -       unsigned int xen_pfn = XEN_PFN_DOWN(phys);
> -       unsigned int bfn = XEN_PFN_DOWN(dev_addr);
> +       unsigned int bfn = XEN_PFN_DOWN(dma_to_phys(dev, dev_addr));
>   
>   	/*
>          * The swiotlb buffer should be used if
> @@ -115,7 +115,7 @@ bool xen_arch_need_swiotlb(struct device *dev,
>          * require a bounce buffer because the device doesn't support coherent
>          * memory and we are not able to flush the cache.
>          */
> -       return (!hypercall_cflush && (xen_pfn != bfn) &&
> +       return (!hypercall_cflush && !pfn_valid(bfn) &&
I believe this change is incorrect. The bfn is a frame based on Xen page 
granularity (always 4K) while pfn_valid() is expecting a frame based on 
the Kernel page granularity.
>                 !dev_is_dma_coherent(dev));
>   }
>   
Cheers,

--
Julien Grall