Re: [PATCH] xen/virtio: Convert PAGE_SIZE/PAGE_SHIFT/PFN_UP to Xen counterparts

[Xenia Ragiadakou <burzalodowa@xxxxxxxxx>]

On 10/6/22 15:09, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
>
> Although XEN_PAGE_SIZE is equal to PAGE_SIZE (4KB) for now, it would
> be more correct to use Xen specific #define-s as XEN_PAGE_SIZE can
> be changed at some point in the future.
>
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> ---
> Cc: Juergen Gross <jgross@xxxxxxxx>
> Cc: Xenia Ragiadakou <burzalodowa@xxxxxxxxx>
>
> As it was proposed at:
> https://lore.kernel.org/xen-devel/20221005174823.1800761-1-olekstysh@xxxxxxxxx/
>
> Should go in only after that series.
> ---
>   drivers/xen/grant-dma-ops.c | 20 ++++++++++----------
>   1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
> index c66f56d24013..5392fdc25dca 100644
> --- a/drivers/xen/grant-dma-ops.c
> +++ b/drivers/xen/grant-dma-ops.c
> @@ -31,12 +31,12 @@ static DEFINE_XARRAY_FLAGS(xen_grant_dma_devices, 
> XA_FLAGS_LOCK_IRQ);
>   
>   static inline dma_addr_t grant_to_dma(grant_ref_t grant)
>   {
> -       return XEN_GRANT_DMA_ADDR_OFF | ((dma_addr_t)grant << PAGE_SHIFT);
> +       return XEN_GRANT_DMA_ADDR_OFF | ((dma_addr_t)grant << XEN_PAGE_SHIFT);
>   }
With this change, can the offset added to the dma handle, generated by 
grant_to_dma(), be the offset in the page? Couldn't it corrupt the grant 
ref?
>   
>   static inline grant_ref_t dma_to_grant(dma_addr_t dma)
>   {
> -       return (grant_ref_t)((dma & ~XEN_GRANT_DMA_ADDR_OFF) >> PAGE_SHIFT);
> +       return (grant_ref_t)((dma & ~XEN_GRANT_DMA_ADDR_OFF) >> XEN_PAGE_SHIFT);
>   }
>   
>   static struct xen_grant_dma_data *find_xen_grant_dma_data(struct device *dev)
> @@ -79,7 +79,7 @@ static void *xen_grant_dma_alloc(struct device *dev, size_t 
> size,
>                                  unsigned long attrs)
>   {
>         struct xen_grant_dma_data *data;
> -       unsigned int i, n_pages = PFN_UP(size);
> +       unsigned int i, n_pages = XEN_PFN_UP(size);
>         unsigned long pfn;
>         grant_ref_t grant;
>         void *ret;
> @@ -91,14 +91,14 @@ static void *xen_grant_dma_alloc(struct device *dev, size_t 
> size,
>         if (unlikely(data->broken))
>                 return NULL;
>   
> -	ret = alloc_pages_exact(n_pages * PAGE_SIZE, gfp);
> +       ret = alloc_pages_exact(n_pages * XEN_PAGE_SIZE, gfp);
>         if (!ret)
>                 return NULL;
>   
>   	pfn = virt_to_pfn(ret);
>   
>   	if (gnttab_alloc_grant_reference_seq(n_pages, &grant)) {
> -               free_pages_exact(ret, n_pages * PAGE_SIZE);
> +               free_pages_exact(ret, n_pages * XEN_PAGE_SIZE);
>                 return NULL;
>         }
>   
> @@ -116,7 +116,7 @@ static void xen_grant_dma_free(struct device *dev, size_t size, void *vaddr,
>                                dma_addr_t dma_handle, unsigned long attrs)
>   {
>         struct xen_grant_dma_data *data;
> -       unsigned int i, n_pages = PFN_UP(size);
> +       unsigned int i, n_pages = XEN_PFN_UP(size);
>         grant_ref_t grant;
>   
>   	data = find_xen_grant_dma_data(dev);
> @@ -138,7 +138,7 @@ static void xen_grant_dma_free(struct device *dev, size_t 
> size, void *vaddr,
>   
>   	gnttab_free_grant_reference_seq(grant, n_pages);
>   
> -	free_pages_exact(vaddr, n_pages * PAGE_SIZE);
> +       free_pages_exact(vaddr, n_pages * XEN_PAGE_SIZE);
>   }
>   
>   static struct page *xen_grant_dma_alloc_pages(struct device *dev, size_t size,
> @@ -168,7 +168,7 @@ static dma_addr_t xen_grant_dma_map_page(struct device 
> *dev, struct page *page,
>                                          unsigned long attrs)
>   {
>         struct xen_grant_dma_data *data;
> -       unsigned int i, n_pages = PFN_UP(offset + size);
> +       unsigned int i, n_pages = XEN_PFN_UP(offset + size);
The offset, here, refers to the offset in the page ...

>         grant_ref_t grant;
>         dma_addr_t dma_handle;
>   
> @@ -200,8 +200,8 @@ static void xen_grant_dma_unmap_page(struct device *dev, dma_addr_t dma_handle,
>                                      unsigned long attrs)
>   {
>         struct xen_grant_dma_data *data;
> -       unsigned long offset = dma_handle & (PAGE_SIZE - 1);
> -       unsigned int i, n_pages = PFN_UP(offset + size);
> +       unsigned long offset = dma_handle & ~XEN_PAGE_MASK;
... while, here, it refers to the offset in the grant.
So, the calculated number of grants may differ.

> +       unsigned int i, n_pages = XEN_PFN_UP(offset + size);
>         grant_ref_t grant;
>   
>   	if (WARN_ON(dir == DMA_NONE))
--
Xenia