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

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Date:   Mon, 16 Jan 2017 15:03:19 +0000
From:   Julien Grall <julien.grall@....com>
To:     Stefano Stabellini <sstabellini@...nel.org>,
        Juergen Gross <jgross@...e.com>
Cc:     Jiandi An <anjiandi@...eaurora.org>, boris.ostrovsky@...cle.com,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] Xen: ARM: Zero reserved fields of xatp before making
 hypervisor call

Hi Stefano,

On 03/01/17 18:03, Stefano Stabellini wrote:
> On Mon, 2 Jan 2017, Juergen Gross wrote:
>> 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.
>
> I don't feel strongly about this either - I think this patch is good
> enough. I'll apply to xentip.

I think this patch should be backported to stable trees because the 
issue could appear depending on the compiler.

Cheers,

-- 
Julien Grall