[Xen-devel] [PATCH RFC v2 06/12] x86: add a xpti command line parameter

[Juergen Gross <jgross@xxxxxxxx>]

Add a command line parameter for controlling Xen page table isolation
(XPTI): per default it is on for non-AMD systems in 64 bit pv domains.

Possible settings are:
- true: switched on even on AMD systems
- false: switched off for all
- nodom0: switched off for dom0

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 docs/misc/xen-command-line.markdown | 18 ++++++++++++
 xen/arch/x86/pv/domain.c            | 55 +++++++++++++++++++++++++++++++++++++
 xen/include/asm-x86/domain.h        |  2 ++
 3 files changed, 75 insertions(+)

diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index f5214defbb..90202a5cc9 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -1911,6 +1911,24 @@ In the case that x2apic is in use, this option switches 
between physical and
 clustered mode.  The default, given no hint from the **FADT**, is cluster
 mode.
 
+### xpti
+> `= nodom0 | default | <boolean>`
+
+> Default: `false` on AMD hardware, `true` everywhere else.
+
+> Can be modified at runtime
+
+Override default selection of whether to isolate 64-bit PV guest page
+tables.
+
+`true` activates page table isolation even on AMD hardware.
+
+`false` deactivates page table isolation on all systems.
+
+`nodom0` deactivates page table isolation for dom0.
+
+`default` switch to default settings.
+
 ### xsave
 > `= <boolean>`
 
diff --git a/xen/arch/x86/pv/domain.c b/xen/arch/x86/pv/domain.c
index 74e9e667d2..7d50f9bc19 100644
--- a/xen/arch/x86/pv/domain.c
+++ b/xen/arch/x86/pv/domain.c
@@ -6,6 +6,7 @@
 
 #include <xen/domain_page.h>
 #include <xen/errno.h>
+#include <xen/init.h>
 #include <xen/lib.h>
 #include <xen/sched.h>
 
@@ -17,6 +18,40 @@
 #undef page_to_mfn
 #define page_to_mfn(pg) _mfn(__page_to_mfn(pg))
 
+static __read_mostly enum {
+    XPTI_DEFAULT,
+    XPTI_ON,
+    XPTI_OFF,
+    XPTI_NODOM0
+} opt_xpti = XPTI_DEFAULT;
+
+static int parse_xpti(const char *s)
+{
+    int rc = 0;
+
+    switch ( parse_bool(s, NULL) )
+    {
+    case 0:
+        opt_xpti = XPTI_OFF;
+        break;
+    case 1:
+        opt_xpti = XPTI_ON;
+        break;
+    default:
+        if ( !strcmp(s, "default") )
+            opt_xpti = XPTI_DEFAULT;
+        else if ( !strcmp(s, "nodom0") )
+            opt_xpti = XPTI_NODOM0;
+        else
+            rc = -EINVAL;
+        break;
+    }
+
+    return rc;
+}
+
+custom_runtime_param("xpti", parse_xpti);
+
 static void noreturn continue_nonidle_domain(struct vcpu *v)
 {
     check_wakeup_from_wait();
@@ -76,6 +111,8 @@ int switch_compat(struct domain *d)
             goto undo_and_fail;
     }
 
+    d->arch.pv_domain.xpti = false;
+
     domain_set_alloc_bitsize(d);
     recalculate_cpuid_policy(d);
 
@@ -212,6 +249,24 @@ int pv_domain_initialise(struct domain *d, unsigned int 
domcr_flags,
     /* 64-bit PV guest by default. */
     d->arch.is_32bit_pv = d->arch.has_32bit_shinfo = 0;
 
+    switch (opt_xpti)
+    {
+    case XPTI_OFF:
+        d->arch.pv_domain.xpti = false;
+        break;
+    case XPTI_ON:
+        d->arch.pv_domain.xpti = true;
+        break;
+    case XPTI_NODOM0:
+        d->arch.pv_domain.xpti = boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
+                                 d->domain_id != 0 &&
+                                 d->domain_id != hardware_domid;
+        break;
+    case XPTI_DEFAULT:
+        d->arch.pv_domain.xpti = boot_cpu_data.x86_vendor != X86_VENDOR_AMD;
+        break;
+    }
+
     return 0;
 
   fail:
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index 4679d5477d..f1230ac621 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -257,6 +257,8 @@ struct pv_domain
     struct mapcache_domain mapcache;
 
     struct cpuidmasks *cpuidmasks;
+
+    bool xpti;
 };
 
 struct monitor_write_data {
-- 
2.13.6


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