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

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Date:	Fri, 3 Jan 2014 10:09:53 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	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 Fri, Jan 03, 2014 at 12:11:42PM +0000, David Vrabel wrote:
> 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.

Excellent suggestion!
> 
> >> 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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