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

From: Julien Grall <[email-masked]>
Date: Wed, 5 Aug 2015 13:33:32 +0100

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