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

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Date:	Tue, 23 Oct 2012 10:46:14 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	mukesh.rathor@...cle.com, Ian.Campbell@...rix.com,
	stefano.stabellini@...citrix.com
Subject: Re: [PATCH 1/6] xen/pvh: Support ParaVirtualized Hardware extensions.

> 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;

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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