linux-kernel - Re: [Xen-devel] [PATCH v2 4/8] xen: Use the correctly the Xen memory terminologies

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Message-ID: <55C2029C.9030705@citrix.com>
Date:	Wed, 5 Aug 2015 13:33:32 +0100
From:	Julien Grall <julien.grall@...rix.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<xen-devel@...ts.xenproject.org>
CC:	<linux-fbdev@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com>,
	"Jiri Slaby" <jslaby@...e.com>,
	Russell King <linux@....linux.org.uk>,
	<linux-scsi@...r.kernel.org>, <x86@...nel.org>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	<linux-input@...r.kernel.org>,
	"Jean-Christophe Plagniol-Villard" <plagnioj@...osoft.com>,
	<ian.campbell@...rix.com>, <stefano.stabellini@...citrix.com>,
	"James E.J. Bottomley" <JBottomley@...n.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	Juergen Gross <jgross@...e.com>, Wei Liu <wei.liu2@...rix.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	<linux-kernel@...r.kernel.org>,
	David Vrabel <david.vrabel@...rix.com>,
	<netdev@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
	Roger Pau Monné <roger.pau@...rix.com>
Subject: Re: [Xen-devel] [PATCH v2 4/8] xen: Use the correctly the Xen memory
 terminologies

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
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