linux-kernel - Re: [PATCH V2] Xen: ARM: Zero reserved fields of xatp before making hypervisor call

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Date:   Mon, 2 Jan 2017 07:13:35 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Jiandi An <anjiandi@...eaurora.org>, boris.ostrovsky@...cle.com,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        sstabellini@...nel.org, julien.grall@....com
Subject: Re: [PATCH V2] Xen: ARM: Zero reserved fields of xatp before making
 hypervisor call

On 28/12/16 01:47, Jiandi An wrote:
> Ensure all reserved fields of xatp are zero before making
> hypervisor call to XEN in xen_map_device_mmio().
> xenmem_add_to_physmap_one() in XEN fails the mapping request if
> extra.res reserved field in xatp is not zero for XENMAPSPACE_dev_mmio
> request.
> 
> Signed-off-by: Jiandi An <anjiandi@...eaurora.org>
> ---
> Changed zeroing xatp to a static initialization
> of .domid and .space for xatp.
> 
>  drivers/xen/arm-device.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/xen/arm-device.c b/drivers/xen/arm-device.c
> index 778acf8..85dd20e 100644
> --- a/drivers/xen/arm-device.c
> +++ b/drivers/xen/arm-device.c
> @@ -58,9 +58,13 @@ static int xen_map_device_mmio(const struct resource *resources,
>  	xen_pfn_t *gpfns;
>  	xen_ulong_t *idxs;
>  	int *errs;
> -	struct xen_add_to_physmap_range xatp;
>  
>  	for (i = 0; i < count; i++) {
> +		struct xen_add_to_physmap_range xatp = {
> +			.domid = DOMID_SELF,
> +			.space = XENMAPSPACE_dev_mmio
> +		};
> +

I still don't see the need to re-initialize the input parts of xatp
on each loop iteration unless you can show the need for it (e.g. a
buggy hypervisor version not conforming to the interface specification).

OTOH I don't feel really strong about it and let Stefano being the
maintainer for the ARM parts decide.


Juergen

>  		r = &resources[i];
>  		nr = DIV_ROUND_UP(resource_size(r), XEN_PAGE_SIZE);
>  		if ((resource_type(r) != IORESOURCE_MEM) || (nr == 0))
> @@ -87,9 +91,7 @@ static int xen_map_device_mmio(const struct resource *resources,
>  			idxs[j] = XEN_PFN_DOWN(r->start) + j;
>  		}
>  
> -		xatp.domid = DOMID_SELF;
>  		xatp.size = nr;
> -		xatp.space = XENMAPSPACE_dev_mmio;
>  
>  		set_xen_guest_handle(xatp.gpfns, gpfns);
>  		set_xen_guest_handle(xatp.idxs, idxs);
>