[v11.1,3/6] sysctl / libxl: report whether IOMMU/HAP page table sharing is supported
diff mbox series

Message ID e79beeb5-7288-c8fd-8823-feaf8d4e7e77@suse.com
State New, archived
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Series
  • Untitled series #173779
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Commit Message

Jan Beulich Sept. 13, 2019, 11:10 a.m. UTC
This patch defines a new bit reported in the hw_cap field of struct
xen_sysctl_physinfo to indicate whether the platform supports sharing of
HAP page tables (i.e. the P2M) with the IOMMU. This informs the toolstack
whether the domain needs extra memory to store discrete IOMMU page tables
or not.

NOTE: This patch makes sure iommu_hap_pt_shared is clear if HAP is not
      supported or the IOMMU is disabled, and defines it to false if
      !CONFIG_HVM.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
---
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Wei Liu <wl@xen.org>
Cc: Anthony PERARD <anthony.perard@citrix.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Julien Grall <julien.grall@arm.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Tim Deegan <tim@xen.org>
Cc: Christian Lindig <christian.lindig@citrix.com>
Cc: David Scott <dave@recoil.org>
Cc: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Cc: Kevin Tian <kevin.tian@intel.com>

v11.1:
 - introduce clear_iommu_hap_pt_share()
 - drop unnecessary "else"

v11:
 - Fix abi-check breakage

v10:
 - Set flag in common code (which means clearing iommu_hap_pt_share if
   HAP cannot be enabled or is configured out).

v9:
 - New in v9
---
 tools/libxl/libxl.c                      |    2 ++
 tools/libxl/libxl.h                      |    7 +++++++
 tools/libxl/libxl_types.idl              |    1 +
 tools/ocaml/libs/xc/xenctrl.ml           |    1 +
 tools/ocaml/libs/xc/xenctrl.mli          |    3 ++-
 tools/xl/xl_info.c                       |    5 +++--
 xen/arch/x86/hvm/hvm.c                   |   26 +++++++++++++++++++-------
 xen/common/sysctl.c                      |    2 ++
 xen/drivers/passthrough/amd/iommu_init.c |    3 ++-
 xen/drivers/passthrough/iommu.c          |   11 ++++++++++-
 xen/drivers/passthrough/vtd/iommu.c      |    2 +-
 xen/include/public/sysctl.h              |    6 +++++-
 xen/include/xen/iommu.h                  |   17 ++++++++++++++++-
 13 files changed, 71 insertions(+), 15 deletions(-)

Comments

Paul Durrant Sept. 13, 2019, 11:47 a.m. UTC | #1
> -----Original Message-----
> From: Jan Beulich <jbeulich@suse.com>
> Sent: 13 September 2019 12:10
> To: Paul Durrant <Paul.Durrant@citrix.com>; xen-devel@lists.xenproject.org
> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>; Julien Grall <julien.grall@arm.com>; Andrew
> Cooper <Andrew.Cooper3@citrix.com>; Anthony Perard <anthony.perard@citrix.com>; Christian Lindig
> <christian.lindig@citrix.com>; Roger Pau Monne <roger.pau@citrix.com>; George Dunlap
> <George.Dunlap@citrix.com>; Ian Jackson <Ian.Jackson@citrix.com>; Kevin Tian <kevin.tian@intel.com>;
> Stefano Stabellini <sstabellini@kernel.org>; Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>; David
> Scott <dave@recoil.org>; Tim (Xen.org) <tim@xen.org>; WeiLiu <wl@xen.org>
> Subject: [PATCH v11.1 3/6] sysctl / libxl: report whether IOMMU/HAP page table sharing is supported
> 
> This patch defines a new bit reported in the hw_cap field of struct
> xen_sysctl_physinfo to indicate whether the platform supports sharing of
> HAP page tables (i.e. the P2M) with the IOMMU. This informs the toolstack
> whether the domain needs extra memory to store discrete IOMMU page tables
> or not.
> 
> NOTE: This patch makes sure iommu_hap_pt_shared is clear if HAP is not
>       supported or the IOMMU is disabled, and defines it to false if
>       !CONFIG_HVM.
> 
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> Acked-by: Christian Lindig <christian.lindig@citrix.com>

Reviewed-by: Paul Durrant <paul.durrant@citrix.com>

...with one observation...

[snip]
> --- a/xen/drivers/passthrough/iommu.c
> +++ b/xen/drivers/passthrough/iommu.c
> @@ -49,7 +49,11 @@ int8_t __hwdom_initdata iommu_hwdom_rese
>   * default until we find a good solution to resolve it.
>   */
>  bool_t __read_mostly iommu_intpost;
> -bool_t __read_mostly iommu_hap_pt_share = 1;
> +
> +#ifndef iommu_hap_pt_share
> +bool __read_mostly iommu_hap_pt_share = true;
> +#endif
> +
>  bool_t __read_mostly iommu_debug;
>  bool_t __read_mostly amd_iommu_perdev_intremap = 1;
> 
> @@ -102,8 +106,10 @@ static int __init parse_iommu_param(cons
>              iommu_hwdom_passthrough = val;
>          else if ( (val = parse_boolean("dom0-strict", s, ss)) >= 0 )
>              iommu_hwdom_strict = val;
> +#ifndef iommu_hap_pt_share
>          else if ( (val = parse_boolean("sharept", s, ss)) >= 0 )
>              iommu_hap_pt_share = val;
> +#endif
>          else
>              rc = -EINVAL;
> 

With this change there will be a command line parse error if 'no-sharept' is passed on the command line to a hypervisor built without CONFIG_HVM. I don't know whether you really want that behaviour, which is why my patch did:

@@ -103,7 +107,14 @@ static int __init parse_iommu_param(const char *s)
         else if ( (val = parse_boolean("dom0-strict", s, ss)) >= 0 )
             iommu_hwdom_strict = val;
         else if ( (val = parse_boolean("sharept", s, ss)) >= 0 )
+        {
+#ifndef iommu_hap_pt_share
             iommu_hap_pt_share = val;
+#else
+            if (val != iommu_hap_pt_share)
+                rc = -EINVAL;
+#endif
+        }
         else
             rc = -EINVAL;

  Paul
Jan Beulich Sept. 13, 2019, 1:29 p.m. UTC | #2
On 13.09.2019 13:47, Paul Durrant wrote:
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@suse.com>
>> Sent: 13 September 2019 12:10
>> To: Paul Durrant <Paul.Durrant@citrix.com>; xen-devel@lists.xenproject.org
>> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>; Julien Grall <julien.grall@arm.com>; Andrew
>> Cooper <Andrew.Cooper3@citrix.com>; Anthony Perard <anthony.perard@citrix.com>; Christian Lindig
>> <christian.lindig@citrix.com>; Roger Pau Monne <roger.pau@citrix.com>; George Dunlap
>> <George.Dunlap@citrix.com>; Ian Jackson <Ian.Jackson@citrix.com>; Kevin Tian <kevin.tian@intel.com>;
>> Stefano Stabellini <sstabellini@kernel.org>; Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>; David
>> Scott <dave@recoil.org>; Tim (Xen.org) <tim@xen.org>; WeiLiu <wl@xen.org>
>> Subject: [PATCH v11.1 3/6] sysctl / libxl: report whether IOMMU/HAP page table sharing is supported
>>
>> This patch defines a new bit reported in the hw_cap field of struct
>> xen_sysctl_physinfo to indicate whether the platform supports sharing of
>> HAP page tables (i.e. the P2M) with the IOMMU. This informs the toolstack
>> whether the domain needs extra memory to store discrete IOMMU page tables
>> or not.
>>
>> NOTE: This patch makes sure iommu_hap_pt_shared is clear if HAP is not
>>       supported or the IOMMU is disabled, and defines it to false if
>>       !CONFIG_HVM.
>>
>> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> Acked-by: Christian Lindig <christian.lindig@citrix.com>
> 
> Reviewed-by: Paul Durrant <paul.durrant@citrix.com>

Thanks.

> ...with one observation...
> 
> [snip]
>> --- a/xen/drivers/passthrough/iommu.c
>> +++ b/xen/drivers/passthrough/iommu.c
>> @@ -49,7 +49,11 @@ int8_t __hwdom_initdata iommu_hwdom_rese
>>   * default until we find a good solution to resolve it.
>>   */
>>  bool_t __read_mostly iommu_intpost;
>> -bool_t __read_mostly iommu_hap_pt_share = 1;
>> +
>> +#ifndef iommu_hap_pt_share
>> +bool __read_mostly iommu_hap_pt_share = true;
>> +#endif
>> +
>>  bool_t __read_mostly iommu_debug;
>>  bool_t __read_mostly amd_iommu_perdev_intremap = 1;
>>
>> @@ -102,8 +106,10 @@ static int __init parse_iommu_param(cons
>>              iommu_hwdom_passthrough = val;
>>          else if ( (val = parse_boolean("dom0-strict", s, ss)) >= 0 )
>>              iommu_hwdom_strict = val;
>> +#ifndef iommu_hap_pt_share
>>          else if ( (val = parse_boolean("sharept", s, ss)) >= 0 )
>>              iommu_hap_pt_share = val;
>> +#endif
>>          else
>>              rc = -EINVAL;
>>
> 
> With this change there will be a command line parse error if 'no-sharept' is passed on the command line to a hypervisor built without CONFIG_HVM. I don't know whether you really want that behaviour, which is why my patch did:
> 
> @@ -103,7 +107,14 @@ static int __init parse_iommu_param(const char *s)
>          else if ( (val = parse_boolean("dom0-strict", s, ss)) >= 0 )
>              iommu_hwdom_strict = val;
>          else if ( (val = parse_boolean("sharept", s, ss)) >= 0 )
> +        {
> +#ifndef iommu_hap_pt_share
>              iommu_hap_pt_share = val;
> +#else
> +            if (val != iommu_hap_pt_share)
> +                rc = -EINVAL;
> +#endif
> +        }
>          else
>              rc = -EINVAL;

Yes, I did change this intentionally, as I think the "sharept" option
(in its positive or negative form) should not be specified to Xen
built with this tied to a fixed value.

Jan
Roger Pau Monné Sept. 13, 2019, 1:53 p.m. UTC | #3
On Fri, Sep 13, 2019 at 01:10:18PM +0200, Jan Beulich wrote:
> --- a/tools/ocaml/libs/xc/xenctrl.mli
> +++ b/tools/ocaml/libs/xc/xenctrl.mli
> @@ -57,7 +57,6 @@ type domain_create_flag =
>    | CDF_OOS_OFF
>    | CDF_XS_DOMAIN
>    | CDF_IOMMU
> -

Stray deletion?

> --- a/xen/include/public/sysctl.h
> +++ b/xen/include/public/sysctl.h
> @@ -96,9 +96,13 @@ struct xen_sysctl_tbuf_op {
>  /* The platform supports software paging. */
>  #define _XEN_SYSCTL_PHYSCAP_shadow       4
>  #define XEN_SYSCTL_PHYSCAP_shadow        (1u<<_XEN_SYSCTL_PHYSCAP_shadow)
> +/* The platform supports sharing of HAP page tables with the IOMMU. */
> +#define _XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share 5
> +#define XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share  \
> +    (1u << _XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share)

I would drop the _hap part of this, since I don't think it adds much,
it's not like the iommu page tables can be shared with anything else?

I don't have a strong opinion, and given that the code already makes
extensive use of iommu_hap_pt_share I would be fine with that.

With the removed newline fixed (if applicable):

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Paul Durrant Sept. 13, 2019, 2:17 p.m. UTC | #4
> -----Original Message-----
> From: Roger Pau Monne <roger.pau@citrix.com>
> Sent: 13 September 2019 14:54
> To: Jan Beulich <jbeulich@suse.com>
> Cc: Paul Durrant <Paul.Durrant@citrix.com>; xen-devel@lists.xenproject.org; Suravee Suthikulpanit
> <suravee.suthikulpanit@amd.com>; Julien Grall <julien.grall@arm.com>; Andrew Cooper
> <Andrew.Cooper3@citrix.com>; Anthony Perard <anthony.perard@citrix.com>; Christian Lindig
> <christian.lindig@citrix.com>; George Dunlap <George.Dunlap@citrix.com>; Ian Jackson
> <Ian.Jackson@citrix.com>; Kevin Tian <kevin.tian@intel.com>; Stefano Stabellini
> <sstabellini@kernel.org>; Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>; David Scott
> <dave@recoil.org>; Tim (Xen.org) <tim@xen.org>; WeiLiu <wl@xen.org>
> Subject: Re: [PATCH v11.1 3/6] sysctl / libxl: report whether IOMMU/HAP page table sharing is
> supported
> 
> On Fri, Sep 13, 2019 at 01:10:18PM +0200, Jan Beulich wrote:
> > --- a/tools/ocaml/libs/xc/xenctrl.mli
> > +++ b/tools/ocaml/libs/xc/xenctrl.mli
> > @@ -57,7 +57,6 @@ type domain_create_flag =
> >    | CDF_OOS_OFF
> >    | CDF_XS_DOMAIN
> >    | CDF_IOMMU
> > -
> 
> Stray deletion?

Yes, it is. It gets fixed up by a later patch though.

> 
> > --- a/xen/include/public/sysctl.h
> > +++ b/xen/include/public/sysctl.h
> > @@ -96,9 +96,13 @@ struct xen_sysctl_tbuf_op {
> >  /* The platform supports software paging. */
> >  #define _XEN_SYSCTL_PHYSCAP_shadow       4
> >  #define XEN_SYSCTL_PHYSCAP_shadow        (1u<<_XEN_SYSCTL_PHYSCAP_shadow)
> > +/* The platform supports sharing of HAP page tables with the IOMMU. */
> > +#define _XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share 5
> > +#define XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share  \
> > +    (1u << _XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share)
> 
> I would drop the _hap part of this, since I don't think it adds much,
> it's not like the iommu page tables can be shared with anything else?
> 
> I don't have a strong opinion, and given that the code already makes
> extensive use of iommu_hap_pt_share I would be fine with that.
> 
> With the removed newline fixed (if applicable):
> 
> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Thanks,

  Paul
Julien Grall Sept. 17, 2019, 9:36 a.m. UTC | #5
Hi Jan,

On 9/13/19 12:10 PM, Jan Beulich wrote:
> This patch defines a new bit reported in the hw_cap field of struct
> xen_sysctl_physinfo to indicate whether the platform supports sharing of
> HAP page tables (i.e. the P2M) with the IOMMU. This informs the toolstack
> whether the domain needs extra memory to store discrete IOMMU page tables
> or not.
> 
> NOTE: This patch makes sure iommu_hap_pt_shared is clear if HAP is not
>        supported or the IOMMU is disabled, and defines it to false if
>        !CONFIG_HVM.
> 
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> Acked-by: Christian Lindig <christian.lindig@citrix.com>

For the common code:

Acked-by: Julien Grall <julien.grall@arm.com>

Cheers,
Tian, Kevin Sept. 25, 2019, 9:22 a.m. UTC | #6
> From: Jan Beulich [mailto:jbeulich@suse.com]
> Sent: Friday, September 13, 2019 7:10 PM
> 
> This patch defines a new bit reported in the hw_cap field of struct
> xen_sysctl_physinfo to indicate whether the platform supports sharing of
> HAP page tables (i.e. the P2M) with the IOMMU. This informs the toolstack
> whether the domain needs extra memory to store discrete IOMMU page
> tables
> or not.
> 
> NOTE: This patch makes sure iommu_hap_pt_shared is clear if HAP is not
>       supported or the IOMMU is disabled, and defines it to false if
>       !CONFIG_HVM.
> 
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> Acked-by: Christian Lindig <christian.lindig@citrix.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

Patch
diff mbox series

--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -402,6 +402,8 @@  int libxl_get_physinfo(libxl_ctx *ctx, l
     physinfo->cap_hap = !!(xcphysinfo.capabilities & XEN_SYSCTL_PHYSCAP_hap);
     physinfo->cap_shadow =
         !!(xcphysinfo.capabilities & XEN_SYSCTL_PHYSCAP_shadow);
+    physinfo->cap_iommu_hap_pt_share =
+        !!(xcphysinfo.capabilities & XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share);
 
     GC_FREE;
     return 0;
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -402,6 +402,13 @@ 
 #define LIBXL_HAVE_PHYSINFO_CAP_HAP_SHADOW 1
 
 /*
+ * LIBXL_HAVE_PHYSINFO_CAP_IOMMU_HAP_PT_SHARE indicates that libxl_physinfo
+ * has a cap_iommu_hap_pt_share field that indicates whether the hardware
+ * supports sharing the IOMMU and HAP page tables.
+ */
+#define LIBXL_HAVE_PHYSINFO_CAP_IOMMU_HAP_PT_SHARE 1
+
+/*
  * libxl ABI compatibility
  *
  * The only guarantee which libxl makes regarding ABI compatibility
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -1027,6 +1027,7 @@  libxl_physinfo = Struct("physinfo", [
     ("cap_hvm_directio", bool), # No longer HVM specific
     ("cap_hap", bool),
     ("cap_shadow", bool),
+    ("cap_iommu_hap_pt_share", bool),
     ], dir=DIR_OUT)
 
 libxl_connectorinfo = Struct("connectorinfo", [
--- a/tools/ocaml/libs/xc/xenctrl.ml
+++ b/tools/ocaml/libs/xc/xenctrl.ml
@@ -110,6 +110,7 @@  type physinfo_cap_flag =
 	| CAP_DirectIO
 	| CAP_HAP
 	| CAP_Shadow
+	| CAP_IOMMU_HAP_PT_SHARE
 
 type physinfo =
 {
--- a/tools/ocaml/libs/xc/xenctrl.mli
+++ b/tools/ocaml/libs/xc/xenctrl.mli
@@ -57,7 +57,6 @@  type domain_create_flag =
   | CDF_OOS_OFF
   | CDF_XS_DOMAIN
   | CDF_IOMMU
-
 type domctl_create_config = {
   ssidref: int32;
   handle: string;
@@ -95,6 +94,8 @@  type physinfo_cap_flag =
   | CAP_DirectIO
   | CAP_HAP
   | CAP_Shadow
+  | CAP_IOMMU_HAP_PT_SHARE
+
 type physinfo = {
   threads_per_core : int;
   cores_per_socket : int;
--- a/tools/xl/xl_info.c
+++ b/tools/xl/xl_info.c
@@ -210,13 +210,14 @@  static void output_physinfo(void)
          info.hw_cap[4], info.hw_cap[5], info.hw_cap[6], info.hw_cap[7]
         );
 
-    maybe_printf("virt_caps              :%s%s%s%s%s%s\n",
+    maybe_printf("virt_caps              :%s%s%s%s%s%s%s\n",
          info.cap_pv ? " pv" : "",
          info.cap_hvm ? " hvm" : "",
          info.cap_hvm && info.cap_hvm_directio ? " hvm_directio" : "",
          info.cap_pv && info.cap_hvm_directio ? " pv_directio" : "",
          info.cap_hap ? " hap" : "",
-         info.cap_shadow ? " shadow" : ""
+         info.cap_shadow ? " shadow" : "",
+         info.cap_iommu_hap_pt_share ? " iommu_hap_pt_share" : ""
         );
 
     vinfo = libxl_get_version_info(ctx);
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -142,6 +142,23 @@  static struct notifier_block cpu_nfb = {
     .notifier_call = cpu_callback
 };
 
+static bool __init hap_supported(const struct hvm_function_table *fns)
+{
+    if ( !fns->hap_supported )
+    {
+        printk("HVM: Hardware Assisted Paging (HAP) not detected\n");
+        return false;
+    }
+
+    if ( !opt_hap_enabled )
+    {
+        printk("HVM: Hardware Assisted Paging (HAP) detected but disabled\n");
+        return false;
+    }
+
+    return true;
+}
+
 static int __init hvm_enable(void)
 {
     const struct hvm_function_table *fns = NULL;
@@ -158,13 +175,8 @@  static int __init hvm_enable(void)
     hvm_enabled = 1;
 
     printk("HVM: %s enabled\n", fns->name);
-    if ( !fns->hap_supported )
-        printk("HVM: Hardware Assisted Paging (HAP) not detected\n");
-    else if ( !opt_hap_enabled )
-    {
-        hvm_funcs.hap_supported = 0;
-        printk("HVM: Hardware Assisted Paging (HAP) detected but disabled\n");
-    }
+    if ( !hap_supported(fns) )
+        clear_iommu_hap_pt_share();
     else
     {
         printk("HVM: Hardware Assisted Paging (HAP) detected\n");
--- a/xen/common/sysctl.c
+++ b/xen/common/sysctl.c
@@ -269,6 +269,8 @@  long do_sysctl(XEN_GUEST_HANDLE_PARAM(xe
         arch_do_physinfo(pi);
         if ( iommu_enabled )
             pi->capabilities |= XEN_SYSCTL_PHYSCAP_directio;
+        if ( iommu_hap_pt_share )
+            pi->capabilities |= XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share;
 
         if ( copy_to_guest(u_sysctl, op, 1) )
             ret = -EFAULT;
--- a/xen/drivers/passthrough/amd/iommu_init.c
+++ b/xen/drivers/passthrough/amd/iommu_init.c
@@ -1406,7 +1406,8 @@  int __init amd_iommu_init(bool xt)
      * since it only supports p2m_ram_rw, and this would
      * prevent doing IO to/from mapped grant frames.
      */
-    iommu_hap_pt_share = 0;
+    clear_iommu_hap_pt_share();
+
     printk(XENLOG_DEBUG "AMD-Vi: Disabled HAP memory map sharing with IOMMU\n");
 
     /* per iommu initialization  */
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -49,7 +49,11 @@  int8_t __hwdom_initdata iommu_hwdom_rese
  * default until we find a good solution to resolve it.
  */
 bool_t __read_mostly iommu_intpost;
-bool_t __read_mostly iommu_hap_pt_share = 1;
+
+#ifndef iommu_hap_pt_share
+bool __read_mostly iommu_hap_pt_share = true;
+#endif
+
 bool_t __read_mostly iommu_debug;
 bool_t __read_mostly amd_iommu_perdev_intremap = 1;
 
@@ -102,8 +106,10 @@  static int __init parse_iommu_param(cons
             iommu_hwdom_passthrough = val;
         else if ( (val = parse_boolean("dom0-strict", s, ss)) >= 0 )
             iommu_hwdom_strict = val;
+#ifndef iommu_hap_pt_share
         else if ( (val = parse_boolean("sharept", s, ss)) >= 0 )
             iommu_hap_pt_share = val;
+#endif
         else
             rc = -EINVAL;
 
@@ -511,7 +517,10 @@  int __init iommu_setup(void)
         iommu_enabled = (rc == 0);
     }
     if ( !iommu_enabled )
+    {
         iommu_intremap = 0;
+        clear_iommu_hap_pt_share();
+    }
 
     if ( (force_iommu && !iommu_enabled) ||
          (force_intremap && !iommu_intremap) )
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -2310,7 +2310,7 @@  static int __init vtd_setup(void)
             iommu_intpost = 0;
 
         if ( !vtd_ept_page_compatible(iommu) )
-            iommu_hap_pt_share = 0;
+            clear_iommu_hap_pt_share();
 
         ret = iommu_set_interrupt(drhd);
         if ( ret )
--- a/xen/include/public/sysctl.h
+++ b/xen/include/public/sysctl.h
@@ -96,9 +96,13 @@  struct xen_sysctl_tbuf_op {
 /* The platform supports software paging. */
 #define _XEN_SYSCTL_PHYSCAP_shadow       4
 #define XEN_SYSCTL_PHYSCAP_shadow        (1u<<_XEN_SYSCTL_PHYSCAP_shadow)
+/* The platform supports sharing of HAP page tables with the IOMMU. */
+#define _XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share 5
+#define XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share  \
+    (1u << _XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share)
 
 /* Max XEN_SYSCTL_PHYSCAP_* constant.  Used for ABI checking. */
-#define XEN_SYSCTL_PHYSCAP_MAX XEN_SYSCTL_PHYSCAP_shadow
+#define XEN_SYSCTL_PHYSCAP_MAX XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share
 
 struct xen_sysctl_physinfo {
     uint32_t threads_per_core;
--- a/xen/include/xen/iommu.h
+++ b/xen/include/xen/iommu.h
@@ -55,7 +55,22 @@  static inline bool_t dfn_eq(dfn_t x, dfn
 extern bool_t iommu_enable, iommu_enabled;
 extern bool_t force_iommu, iommu_verbose, iommu_igfx;
 extern bool_t iommu_snoop, iommu_qinval, iommu_intremap, iommu_intpost;
-extern bool_t iommu_hap_pt_share;
+
+#ifdef CONFIG_HVM
+extern bool iommu_hap_pt_share;
+#else
+#define iommu_hap_pt_share false
+#endif
+
+static inline void clear_iommu_hap_pt_share(void)
+{
+#ifndef iommu_hap_pt_share
+    iommu_hap_pt_share = false;
+#elif iommu_hap_pt_share
+    ASSERT_UNREACHABLE();
+#endif
+}
+
 extern bool_t iommu_debug;
 extern bool_t amd_iommu_perdev_intremap;