linux-kernel - Re: [Xen-devel] [RFC 02/23] xen/xenbus: client: Fix call of virt_to_mfn in xenbus_grant

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Date:	Tue, 19 May 2015 14:51:50 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Julien Grall <julien.grall@...rix.com>,
	<xen-devel@...ts.xenproject.org>
CC:	Wei Liu <wei.liu2@...rix.com>, <ian.campbell@...rix.com>,
	<stefano.stabellini@...citrix.com>, <tim@....org>,
	<linux-kernel@...r.kernel.org>,
	David Vrabel <david.vrabel@...rix.com>,
	"Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Xen-devel] [RFC 02/23] xen/xenbus: client: Fix call of virt_to_mfn
 in xenbus_grant_ring

On 14/05/15 18:00, Julien Grall wrote:
> virt_to_mfn should take a void* rather an unsigned long. While it
> doesn't really matter now, it would throw a compiler warning later when
> virt_to_mfn will enforce the type.
> 
> At the same time, avoid to compute new virtual address every time in the
> loop and directly increment the parameter as we don't use it later.

Reviewed-by: David Vrabel <david.vrabel@...rix.com>

But...

> --- a/drivers/xen/xenbus/xenbus_client.c
> +++ b/drivers/xen/xenbus/xenbus_client.c
> @@ -379,16 +379,16 @@ int xenbus_grant_ring(struct xenbus_device *dev, void *vaddr,
>  	int i, j;
>  
>  	for (i = 0; i < nr_pages; i++) {
> -		unsigned long addr = (unsigned long)vaddr +
> -			(PAGE_SIZE * i);
>  		err = gnttab_grant_foreign_access(dev->otherend_id,
> -						  virt_to_mfn(addr), 0);
> +						  virt_to_mfn(vaddr), 0);
>  		if (err < 0) {
>  			xenbus_dev_fatal(dev, err,
>  					 "granting access to ring page");
>  			goto fail;
>  		}
>  		grefs[i] = err;
> +
> +		vaddr = (char *)vaddr + PAGE_SIZE;

You don't need the cast here since vaddr is a void *.

David
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