[Xen-devel] [PATCH 05/10] x86/cpuid: Handle leaf 0x5 in guest_cpuid()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

The MONITOR flag isn't exposed to guests.  The existing toolstack logic, and
pv_cpuid() in the hypervisor, zero the MONITOR leaf for queries.

However, the MONITOR leaf is still visible in the hardware domains native
CPUID view, and Linux depends on this to set up C-state information.  Leak the
hosts MONITOR leaf under the same circumstances that the MONITOR feature is
leaked.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
---
 xen/arch/x86/cpuid.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
index ca38d04..7862d62 100644
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -166,6 +166,8 @@ static void recalculate_misc(struct cpuid_policy *p)
     /* Leaves with subleaf unions. */
     p->basic.raw[0x4] = p->basic.raw[0x7] = p->basic.raw[0xd] = EMPTY_LEAF;
 
+    p->basic.raw[0x5] = EMPTY_LEAF; /* MONITOR not exposed to guests. */
+
     p->basic.raw[0x8] = EMPTY_LEAF;
     p->basic.raw[0xc] = EMPTY_LEAF;
 
@@ -641,13 +643,12 @@ static void pv_cpuid(uint32_t leaf, uint32_t subleaf, 
struct cpuid_leaf *res)
             res->a = (res->a & ~0xff) | 3;
         break;
 
-    case 0x00000005: /* MONITOR/MWAIT */
     case 0x0000000b: /* Extended Topology Enumeration */
     unsupported:
         *res = EMPTY_LEAF;
         break;
 
-    case 0x0 ... 0x4:
+    case 0x0 ... 0x5:
     case 0x7 ... 0x9:
     case 0xc ... XSTATE_CPUID:
     case 0x80000000 ... 0xffffffff:
@@ -682,7 +683,7 @@ static void hvm_cpuid(uint32_t leaf, uint32_t subleaf, 
struct cpuid_leaf *res)
             res->a = (res->a & ~0xff) | 3;
         break;
 
-    case 0x0 ... 0x4:
+    case 0x0 ... 0x5:
     case 0x7 ... 0x9:
     case 0xc ... XSTATE_CPUID:
     case 0x80000000 ... 0xffffffff:
@@ -743,6 +744,7 @@ void guest_cpuid(const struct vcpu *v, uint32_t leaf,
             goto legacy;
 
         case 0x0 ... 0x3:
+        case 0x5:
         case 0x8 ... 0x9:
         case 0xc:
             *res = p->basic.raw[leaf];
@@ -928,6 +930,18 @@ void guest_cpuid(const struct vcpu *v, uint32_t leaf,
         /* Adjustments common with leaf 0x80000001. */
         goto common_dynamic_adjustments;
 
+    case 0x5:
+        /*
+         * Leak the hardware MONITOR leaf under the same conditions that the
+         * MONITOR feature flag is leaked.  See above for details.
+         */
+        regs = guest_cpu_user_regs();
+        if ( is_pv_domain(d) && is_hardware_domain(d) &&
+             guest_kernel_mode(v, regs) && cpu_has_monitor &&
+             regs->entry_vector == TRAP_gp_fault )
+            *res = raw_policy.basic.raw[leaf];
+        break;
+
     case 0x7:
         switch ( subleaf )
         {
-- 
2.1.4


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