linux-kernel - Re: [Xen-devel] [PATCH v4] xen/grant-table: Avoid m2p

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Message-ID: <52E015F5.70408@citrix.com>
Date:	Wed, 22 Jan 2014 19:03:17 +0000
From:	Zoltan Kiss <zoltan.kiss@...rix.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	<ian.campbell@...rix.com>, <wei.liu2@...rix.com>,
	<xen-devel@...ts.xenproject.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <jonathan.davies@...rix.com>
Subject: Re: [Xen-devel] [PATCH v4] xen/grant-table: Avoid m2p_override during
 mapping

On 22/01/14 18:50, Stefano Stabellini wrote:
> On Wed, 22 Jan 2014, Zoltan Kiss wrote:
>> On 22/01/14 16:39, Stefano Stabellini wrote:
>>> On Tue, 21 Jan 2014, Zoltan Kiss wrote:
>>>> @@ -121,7 +125,7 @@ static inline unsigned long mfn_to_pfn(unsigned long
>>>> mfn)
>>>>    		pfn = m2p_find_override_pfn(mfn, ~0);
>>>>    	}
>>>>
>>>> -	/*
>>>> +	/*
>>>
>>> Spurious change?
>> It removes a stray space from the original code. Not necessary, but if it's
>> there, I think we can keep it.
>
> Usually cosmetic changes are done in a separate patch, or at the very
> least they are mentioned in the commit message.
Ok, I'll mention it.
>
>
>>>> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
>>>> index 2ae8699..0060178 100644
>>>> --- a/arch/x86/xen/p2m.c
>>>> +++ b/arch/x86/xen/p2m.c
>>>> @@ -872,15 +872,13 @@ static unsigned long mfn_hash(unsigned long mfn)
>>>>
>>>>    /* Add an MFN override for a particular page */
>>>>    int m2p_add_override(unsigned long mfn, struct page *page,
>>>> -		struct gnttab_map_grant_ref *kmap_op)
>>>> +		struct gnttab_map_grant_ref *kmap_op, unsigned long pfn)
>>>
>>> Do we really need to add another additional parameter to
>>> m2p_add_override?
>>> I would just let m2p_add_override and m2p_remove_override call
>>> page_to_pfn again. It is not that expensive.
>> Yes, because that page_to_pfn can return something different. That's why the
>> v2 patches failed.
>
> I am really curious: how can page_to_pfn return something different?
> I don't think is supposed to happen.
You call set_phys_to_machine before calling m2p* functions.

Zoli

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