linux-kernel - Re: [PATCH 1/6] xen/pvh: Support ParaVirtualized Hardware extensions.

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Date:	Wed, 24 Oct 2012 10:27:52 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"mukesh.rathor@...cle.com" <mukesh.rathor@...cle.com>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>
Subject: Re: [PATCH 1/6] xen/pvh: Support ParaVirtualized Hardware
 extensions.

On Tue, 2012-10-23 at 15:46 +0100, Konrad Rzeszutek Wilk wrote:
> > diff --git a/include/xen/interface/memory.h b/include/xen/interface/memory.h
> > index b66d04c..8beebdb 100644
> > --- a/include/xen/interface/memory.h
> > +++ b/include/xen/interface/memory.h
> > @@ -169,7 +169,13 @@ struct xen_add_to_physmap {
> >      /* Source mapping space. */
> >  #define XENMAPSPACE_shared_info 0 /* shared info page */
> >  #define XENMAPSPACE_grant_table 1 /* grant table page */
> > -    unsigned int space;
> > +#define XENMAPSPACE_gmfn        2 /* GMFN */
> > +#define XENMAPSPACE_gmfn_range  3 /* GMFN range */
> > +#define XENMAPSPACE_gmfn_foreign 4 /* GMFN from another guest */
> > +    uint16_t space;
> > +    domid_t foreign_domid;         /* IFF XENMAPSPACE_gmfn_foreign */
> > +
> > +#define XENMAPIDX_grant_table_status 0x80000000
> >  
> >      /* Index into source mapping space. */
> >      xen_ulong_t idx;
> 
> And this breaks 32-bit PVHVM :-(
> 
> The reason being that in xen_hvm_init_shared_info we allocate the
> structure on the stack, and do not clear the foreign_domid to zero.
> 
> This means we can (and do get) for the argument space, something
> like this:
> 	xatp.space == 0xffff0001;
> instead of
> 	xatp.space = 0x1;

We should be reverting this patch and using XENMEM_add_to_physmap range
instead, see my "xen: x86 pvh: use XENMEM_add_to_physmap_range for
foreign gmfn mappings" from last week.

Mukesh wanted to go with this original version in the interim so
probably fixing it as you have makes sense anyhow.

> 
> This fixes it:
> 
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index e3497f2..b679f86 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -1509,6 +1509,7 @@ void __ref xen_hvm_init_shared_info(void)
>  	xatp.domid = DOMID_SELF;
>  	xatp.idx = 0;
>  	xatp.space = XENMAPSPACE_shared_info;
> +	xatp.foreign_domid = 0;
>  	xatp.gpfn = __pa(shared_info_page) >> PAGE_SHIFT;
>  	if (HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp))
>  		BUG();
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index b2b0a37..cbfd929 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -1044,6 +1044,7 @@ static int gnttab_map(unsigned int start_idx, unsigned int end_idx)
>  		do {
>  			xatp.domid = DOMID_SELF;
>  			xatp.idx = i;
> +			xatp.foreign_domid = 0;
>  			xatp.space = XENMAPSPACE_grant_table;
>  			xatp.gpfn = (xen_hvm_resume_frames >> PAGE_SHIFT) + i;
>  			rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp);


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