[Xen-devel] [PATCH] x86: Allow PV guest set X86_CR4_PCE flag

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

With added PV support for VPMU, guests may legitimately decide to set
CR4's PCE flag. We should allow this when VPMU is enabled.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 xen/arch/x86/cpu/vpmu.c      | 19 +++++++++++++++++++
 xen/arch/x86/domain.c        | 13 ++++++++++++-
 xen/include/asm-x86/domain.h |  2 ++
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/cpu/vpmu.c b/xen/arch/x86/cpu/vpmu.c
index 8af3df1..8cac04e 100644
--- a/xen/arch/x86/cpu/vpmu.c
+++ b/xen/arch/x86/cpu/vpmu.c
@@ -81,6 +81,12 @@ static void __init parse_vpmu_param(char *s)
     }
 }
 
+static void update_cr4_mask_pce(bool_t allow)
+{
+    pv_guest_update_cr4_mask(X86_CR4_PCE, 0, allow);
+    pv_guest_update_cr4_mask(X86_CR4_PCE, 1, allow);
+}
+
 void vpmu_lvtpc_update(uint32_t val)
 {
     struct vpmu_struct *vpmu;
@@ -475,6 +481,7 @@ void vpmu_initialise(struct vcpu *v)
             printk(XENLOG_G_WARNING "VPMU: Unknown CPU vendor %d. "
                    "Disabling VPMU\n", vendor);
             opt_vpmu_enabled = 0;
+            update_cr4_mask_pce(0);
             vpmu_mode = XENPMU_MODE_OFF;
         }
         return; /* Don't bother restoring vpmu_count, VPMU is off forever */
@@ -679,7 +686,16 @@ long do_xenpmu_op(unsigned int op, 
XEN_GUEST_HANDLE_PARAM(xen_pmu_params_t) arg)
         if ( (vpmu_count == 0) ||
              ((vpmu_mode ^ pmu_params.val) ==
               (XENPMU_MODE_SELF | XENPMU_MODE_HV)) )
+        {
+            if ( (vpmu_mode != XENPMU_MODE_OFF) &&
+                 (pmu_params.val == XENPMU_MODE_OFF) )
+                update_cr4_mask_pce(0);
+            else if ( (vpmu_mode == XENPMU_MODE_OFF) &&
+                      (pmu_params.val != XENPMU_MODE_OFF) )
+                update_cr4_mask_pce(1);
+
             vpmu_mode = pmu_params.val;
+        }
         else if ( vpmu_mode != pmu_params.val )
         {
             printk(XENLOG_WARNING
@@ -807,8 +823,11 @@ static int __init vpmu_init(void)
     }
 
     if ( vpmu_mode != XENPMU_MODE_OFF )
+    {
+        update_cr4_mask_pce(1);
         printk(XENLOG_INFO "VPMU: version " __stringify(XENPMU_VER_MAJ) "."
                __stringify(XENPMU_VER_MIN) "\n");
+    }
     else
         opt_vpmu_enabled = 0;
 
diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 045f6ff..71a2bb3 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -738,7 +738,18 @@ static int __init init_pv_cr4_masks(void)
 
     return 0;
 }
-__initcall(init_pv_cr4_masks);
+presmp_initcall(init_pv_cr4_masks);
+
+void pv_guest_update_cr4_mask(unsigned long mask, bool_t is_compat,
+                              bool_t allow)
+{
+    unsigned long *curr_mask = is_compat ? &compat_pv_cr4_mask : &pv_cr4_mask;
+
+    if ( !allow )
+        *curr_mask |= mask;
+    else
+        *curr_mask &= ~mask;
+}
 
 unsigned long pv_guest_cr4_fixup(const struct vcpu *v, unsigned long guest_cr4)
 {
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index 0fce09e..9758b0a 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -561,6 +561,8 @@ void vcpu_show_registers(const struct vcpu *);
 
 /* Clean up CR4 bits that are not under guest control. */
 unsigned long pv_guest_cr4_fixup(const struct vcpu *, unsigned long guest_cr4);
+void pv_guest_update_cr4_mask(unsigned long mask, bool_t is_compat,
+                              bool_t allow);
 
 /* Convert between guest-visible and real CR4 values. */
 #define pv_guest_cr4_to_real_cr4(v)                         \
-- 
1.8.1.4


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