linux-kernel - Re: [Xen-devel] [PATCH v12 14/18] xen/grant: Implement an grant frame array struct.

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Message-ID: <52C6A8FE.5000500@citrix.com>
Date:	Fri, 3 Jan 2014 12:11:42 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	David Vrabel <david.vrabel@...rix.com>,
	<xen-devel@...ts.xenproject.org>, <boris.ostrovsky@...cle.com>,
	<linux-kernel@...r.kernel.org>, <stefano.stabellini@...citrix.com>
Subject: Re: [Xen-devel] [PATCH v12 14/18] xen/grant: Implement an grant frame
 array struct.

On 02/01/14 18:47, Konrad Rzeszutek Wilk wrote:
> On Thu, Jan 02, 2014 at 04:27:19PM +0000, David Vrabel wrote:
>> On 01/01/14 04:35, Konrad Rzeszutek Wilk wrote:
>>> The 'xen_hvm_resume_frames' used to be an 'unsigned long'
>>> and contain the virtual address of the grants. That was OK
>>> for most architectures (PVHVM, ARM) were the grants are contingous
>>> in memory. That however is not the case for PVH - in which case
>>> we will have to do a lookup for each virtual address for the PFN.
>>>
>>> Instead of doing that, lets make it a structure which will contain
>>> the array of PFNs, the virtual address and the count of said PFNs.
>>>
>>> Also provide a generic functions: gnttab_setup_auto_xlat_frames and
>>> gnttab_free_auto_xlat_frames to populate said structure with
>>> appropiate values for PVHVM and ARM.
>>>
>>> To round it off, change the name from 'xen_hvm_resume_frames' to
>>> a more descriptive one - 'xen_auto_xlat_grant_frames'.
>>>
>>> For PVH, in patch "xen/pvh: Piggyback on PVHVM for grant driver"
>>> we will populate the 'xen_auto_xlat_grant_frames' by ourselves.
>> [...]
>>> --- a/drivers/xen/grant-table.c
>>> +++ b/drivers/xen/grant-table.c
>> [...]
>>> @@ -838,6 +838,40 @@ unsigned int gnttab_max_grant_frames(void)
>>>  }
>>>  EXPORT_SYMBOL_GPL(gnttab_max_grant_frames);
>>>  
>>> +int gnttab_setup_auto_xlat_frames(unsigned long addr)
>>> +{
>>> +	xen_pfn_t *pfn;
>>> +	unsigned int max_nr_gframes = __max_nr_grant_frames();
>>> +	int i;
>>> +
>>> +	if (xen_auto_xlat_grant_frames.count)
>>> +		return -EINVAL;
>>> +
>>> +	pfn = kcalloc(max_nr_gframes, sizeof(pfn[0]), GFP_KERNEL);
>>> +	if (!pfn)
>>> +		return -ENOMEM;
>>> +	for (i = 0; i < max_nr_gframes; i++)
>>> +		pfn[i] = PFN_DOWN(addr + (i * PAGE_SIZE));
>>
>> PFN_DOWN(addr) + i looks better to me.
>>
>>> +
>>> +	xen_auto_xlat_grant_frames.vaddr = addr;

I think you should move the xen_remap() call here.

>> Huh? addr is a physical address but you're assigning it to a field
>> called vaddr?  I think you mean to set this field to the result of the
>> xen_remap() call, yes?
> 
> It ends up doing that in gnttab_init. Not to
> xen_auto_xlat_grant_frames.vaddr but to gnttab_shared.addr.

David
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