[PATCHv2 3/3] x86/hvm: add HVM_PARAM_X87_FIP_WIDTH

[David Vrabel <david.vrabel@citrix.com>]

The HVM parameter HVM_PARAM_X87_FIP_WIDTH to allow tools and the guest
to adjust the width of the FIP/FDP registers to be saved/restored by
the hypervisor.  This is in case the hypervisor hueristics do not do
the right thing.

Add this parameter to the set saved during domain save/migrate.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
 tools/libxc/xc_sr_save_x86_hvm.c |  1 +
 xen/arch/x86/hvm/hvm.c           | 13 +++++++++++++
 xen/include/public/hvm/params.h  | 24 +++++++++++++++++++++++-
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/tools/libxc/xc_sr_save_x86_hvm.c b/tools/libxc/xc_sr_save_x86_hvm.c
index e347b3b..ba50a43 100644
--- a/tools/libxc/xc_sr_save_x86_hvm.c
+++ b/tools/libxc/xc_sr_save_x86_hvm.c
@@ -76,6 +76,7 @@ static int write_hvm_params(struct xc_sr_context *ctx)
         HVM_PARAM_VM_GENERATION_ID_ADDR,
         HVM_PARAM_IOREQ_SERVER_PFN,
         HVM_PARAM_NR_IOREQ_SERVER_PAGES,
+        HVM_PARAM_X87_FIP_WIDTH,
     };
 
     xc_interface *xch = ctx->xch;
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index fe382ce..3583c9e 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -6027,6 +6027,7 @@ static int hvm_allow_set_param(struct domain *d,
     case HVM_PARAM_VM_GENERATION_ID_ADDR:
     case HVM_PARAM_STORE_EVTCHN:
     case HVM_PARAM_CONSOLE_EVTCHN:
+    case HVM_PARAM_X87_FIP_WIDTH:
         break;
     /*
      * The following parameters must not be set by the guest
@@ -6222,6 +6223,14 @@ static int hvmop_set_param(
 
         break;
     }
+    case HVM_PARAM_X87_FIP_WIDTH:
+        if ( a.value != 0 && a.value != 4 && a.value != 8 )
+        {
+            rc = -EINVAL;
+            break;
+        }
+        d->arch.x87_fip_width = a.value;
+        break;
     }
 
     if ( rc != 0 )
@@ -6258,6 +6267,7 @@ static int hvm_allow_get_param(struct domain *d,
     case HVM_PARAM_CONSOLE_PFN:
     case HVM_PARAM_CONSOLE_EVTCHN:
     case HVM_PARAM_ALTP2M:
+    case HVM_PARAM_X87_FIP_WIDTH:
         break;
     /*
      * The following parameters must not be read by the guest
@@ -6307,6 +6317,9 @@ static int hvmop_get_param(
     case HVM_PARAM_ACPI_S_STATE:
         a.value = d->arch.hvm_domain.is_s3_suspended ? 3 : 0;
         break;
+    case HVM_PARAM_X87_FIP_WIDTH:
+        a.value = d->arch.x87_fip_width;
+        break;
     case HVM_PARAM_IOREQ_PFN:
     case HVM_PARAM_BUFIOREQ_PFN:
     case HVM_PARAM_BUFIOREQ_EVTCHN:
diff --git a/xen/include/public/hvm/params.h b/xen/include/public/hvm/params.h
index 81f9451..73d4718 100644
--- a/xen/include/public/hvm/params.h
+++ b/xen/include/public/hvm/params.h
@@ -210,6 +210,28 @@
 /* Boolean: Enable altp2m */
 #define HVM_PARAM_ALTP2M       35
 
-#define HVM_NR_PARAMS          36
+/*
+ * Size of the x87 FPU FIP/FDP registers that the hypervisor needs to
+ * save/restore.  This is a workaround for a hardware limitation that
+ * does not allow the full FIP/FDP and FCS/FDS to be restored.
+ *
+ * Valid values are:
+ *
+ * 8: save/restore 64-bit FIP/FDP and clear FCS/FDS (default if CPU
+ *    has FPCSDS feature).
+ *
+ * 4: save/restore 32-bit FIP/FDP, FCS/FDS, and clear upper 32-bits of
+ *    FIP/FDP.
+ *
+ * 0: allow hypervisor to choose based on the value of FIP/FDP
+ *    (default if CPU does not have FPCSDS).
+ *
+ * If FPCSDS (bit 13 in CPUID leaf 0x7, subleaf 0x0) is set, the CPU
+ * never saves FCS/FDS and this parameter should be left at the
+ * default of 8.
+ */
+#define HVM_PARAM_X87_FIP_WIDTH 36
+
+#define HVM_NR_PARAMS 37
 
 #endif /* __XEN_PUBLIC_HVM_PARAMS_H__ */
-- 
2.1.4