linux-kernel - Re: [PATCH v3 10/21] xen/shbuf: switch xen-front-pgdir-shbuf to use INVALID_GRANT

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Date:   Mon, 9 May 2022 11:47:13 +0300
From:   Oleksandr <olekstysh@...il.com>
To:     Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Subject: Re: [PATCH v3 10/21] xen/shbuf: switch xen-front-pgdir-shbuf to use
 INVALID_GRANT_REF


On 05.05.22 11:16, Juergen Gross wrote:


Hello Juergen


> Instead of using a private macro for an invalid grant reference use
> the common one.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
> V3:
> - terminate grant ref list with 0 (Oleksandr Tyshchenko)


Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>


> ---
>   drivers/xen/xen-front-pgdir-shbuf.c | 18 +++++-------------
>   1 file changed, 5 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/xen/xen-front-pgdir-shbuf.c b/drivers/xen/xen-front-pgdir-shbuf.c
> index a959dee21134..b6433761d42c 100644
> --- a/drivers/xen/xen-front-pgdir-shbuf.c
> +++ b/drivers/xen/xen-front-pgdir-shbuf.c
> @@ -21,15 +21,6 @@
>   
>   #include <xen/xen-front-pgdir-shbuf.h>
>   
> -#ifndef GRANT_INVALID_REF
> -/*
> - * FIXME: usage of grant reference 0 as invalid grant reference:
> - * grant reference 0 is valid, but never exposed to a PV driver,
> - * because of the fact it is already in use/reserved by the PV console.
> - */
> -#define GRANT_INVALID_REF	0
> -#endif
> -
>   /**
>    * This structure represents the structure of a shared page
>    * that contains grant references to the pages of the shared
> @@ -38,6 +29,7 @@
>    */
>   struct xen_page_directory {
>   	grant_ref_t gref_dir_next_page;
> +#define XEN_GREF_LIST_END	0
>   	grant_ref_t gref[1]; /* Variable length */
>   };
>   
> @@ -83,7 +75,7 @@ grant_ref_t
>   xen_front_pgdir_shbuf_get_dir_start(struct xen_front_pgdir_shbuf *buf)
>   {
>   	if (!buf->grefs)
> -		return GRANT_INVALID_REF;
> +		return INVALID_GRANT_REF;
>   
>   	return buf->grefs[0];
>   }
> @@ -142,7 +134,7 @@ void xen_front_pgdir_shbuf_free(struct xen_front_pgdir_shbuf *buf)
>   		int i;
>   
>   		for (i = 0; i < buf->num_grefs; i++)
> -			if (buf->grefs[i] != GRANT_INVALID_REF)
> +			if (buf->grefs[i] != INVALID_GRANT_REF)
>   				gnttab_end_foreign_access(buf->grefs[i], 0UL);
>   	}
>   	kfree(buf->grefs);
> @@ -355,7 +347,7 @@ static void backend_fill_page_dir(struct xen_front_pgdir_shbuf *buf)
>   	}
>   	/* Last page must say there is no more pages. */
>   	page_dir = (struct xen_page_directory *)ptr;
> -	page_dir->gref_dir_next_page = GRANT_INVALID_REF;
> +	page_dir->gref_dir_next_page = XEN_GREF_LIST_END;
>   }
>   
>   /**
> @@ -384,7 +376,7 @@ static void guest_fill_page_dir(struct xen_front_pgdir_shbuf *buf)
>   
>   		if (grefs_left <= XEN_NUM_GREFS_PER_PAGE) {
>   			to_copy = grefs_left;
> -			page_dir->gref_dir_next_page = GRANT_INVALID_REF;
> +			page_dir->gref_dir_next_page = XEN_GREF_LIST_END;
>   		} else {
>   			to_copy = XEN_NUM_GREFS_PER_PAGE;
>   			page_dir->gref_dir_next_page = buf->grefs[i + 1];

-- 
Regards,

Oleksandr Tyshchenko