From mboxrd@z Thu Jan  1 00:00:00 1970
From: Julien Grall <julien.grall@citrix.com>
Subject: Re: [Xen-devel] [PATCH v2 4/8] xen: Use the correctly the Xen memory
 terminologies
Date: Wed, 5 Aug 2015 13:33:32 +0100
Message-ID: <55C2029C.9030705@citrix.com>
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Cc: <linux-fbdev@vger.kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	"Jiri Slaby" <jslaby@suse.com>,
	Russell King <linux@arm.linux.org.uk>,
	<linux-scsi@vger.kernel.org>, <x86@kernel.org>,
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	"Jean-Christophe Plagniol-Villard" <plagnioj@jcrosoft.com>,
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	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	<linux-arm-kernel@lists.infradead.org>,
	Juergen Gross <jgross@suse.com>, Wei Liu <wei.liu2@citrix.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	<linux-kernel@vger.kernel.org>,
	David Vrabel <david.vrabel@citrix.com>,
	<netdev@vger.kernel.org>, <linuxppc-dev@lists.ozlabs.org>,
	=?windows-1252?Q?Roger_Pau_Monn=E9?= <roger.pau@citrix.
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	<xen-devel@lists.xenproject.org>
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On 05/08/15 13:19, Boris Ostrovsky wrote:
> On 08/05/2015 06:51 AM, Julien Grall wrote:
>>
>>>> diff --git a/drivers/video/fbdev/xen-fbfront.c
>>>> b/drivers/video/fbdev/xen-fbfront.c
>>>> index 09dc447..25e3cce 100644
>>>> --- a/drivers/video/fbdev/xen-fbfront.c
>>>> +++ b/drivers/video/fbdev/xen-fbfront.c
>>>> @@ -539,7 +539,7 @@ static int xenfb_remove(struct xenbus_device *dev)
>>>>      static unsigned long vmalloc_to_mfn(void *address)
>>>>    {
>>>> -    return pfn_to_mfn(vmalloc_to_pfn(address));
>>>> +    return pfn_to_gfn(vmalloc_to_pfn(address));
>>>>    }
>>> Are you sure? This will return vmalloc_to_pfn(address)).
>> I guess you mean vmalloc_to_mfn will return vmalloc_to_pfn?
>>
>> If so, it will be only the case on auto-translated case (because pfn ==
>> gfn). In the case of PV, the mfn will be returned.
> 
> How will mfn be returned on PV when pfn_to_gfn() is an identity function?
> 
> static inline unsigned long pfn_to_gfn(unsigned long pfn)
>  {
>      return pfn;
>  }

The identity function is only for ARM guest which are always
auto-translated (arch/arm/include/asm/xen/page.h).

The x86 version contains a check if the guest is auto-translated or not
(arch/x86/include/asm/xen/page.):

static inline unsigned long pfn_to_gfn(unsigned long pfn)
{
        if (xen_feature(XENFEAT_auto_translated_physmap))
                return pfn;
        else
                return pfn_to_mfn(pfn);
}

Regards,

-- 
Julien Grall