linux-kernel - Re: [Xen-devel] [PATCH v8] xen/grant-table: Avoid m2p

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Message-ID: <52F52908.4080205@citrix.com>
Date:	Fri, 7 Feb 2014 18:42:16 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, <x86@...nel.org>,
	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
	Roger Pau Monné <roger.pau@...rix.com>,
	Jan Beulich <jbeulich@...e.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	<stefano.stabellini@...citrix.com>
Subject: Re: [Xen-devel] [PATCH v8] xen/grant-table: Avoid m2p_override during
 mapping

On 06/02/14 12:56, Zoltan Kiss wrote:
> The grant mapping API does m2p_override unnecessarily: only gntdev needs it,
> for blkback and future netback patches it just cause a lock contention, as
> those pages never go to userspace. Therefore this series does the following:
> - the original functions were renamed to __gnttab_[un]map_refs, with a new
>   parameter m2p_override
> - based on m2p_override either they follow the original behaviour, or just set
>   the private flag and call set_phys_to_machine
> - gnttab_[un]map_refs are now a wrapper to call __gnttab_[un]map_refs with
>   m2p_override false
> - a new function gnttab_[un]map_refs_userspace provides the old behaviour
> - it cuts out common parts from m2p_*_override functions to
>   *_foreign_p2m_mapping functions
> 
> It also removes a stray space from page.h and change ret to 0 if
> XENFEAT_auto_translated_physmap, as that is the only possible return value
> there.
> 
> v2:

Please put this version information after the '---' marker.  It doesn't
need to end up in the commit message.

> @@ -955,10 +957,12 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
>  			set_phys_to_machine(map_ops[i].host_addr >> PAGE_SHIFT,
>  					map_ops[i].dev_bus_addr >> PAGE_SHIFT);
>  		}
> -		return ret;
> +		return 0;
>  	}
>  
> -	if (!in_interrupt() && paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
> +	if (m2p_override &&
> +	    !in_interrupt() &&
> +	    paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
>  		arch_enter_lazy_mmu_mode();
>  		lazy = true;
>  	}

I think this block and the loop should be in an arch-specific function
(e.g., set_foreign_p2m_mappings(), but I would like to hear Stefano's
opinion.

Similarly for clear_foreign_p2m_mappings().

David
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