[Xen-devel] [PATCH] x86/HVM: hide features dependent on XSAVE when booted with "no-xsave"

["Jan Beulich" <JBeulich@xxxxxxxx>]

... or when the guest has the XSAVE feature hidden by CPUID policy.
Not doing so is at best confusing to guests.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
One question is whether we shouldn't switch leaf 7 to white listing,
just like done for PV guests.

--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -265,7 +265,8 @@ static void __cpuinit generic_identify(s
        if ( c->cpuid_level >= 0x00000007 )
                cpuid_count(0x00000007, 0, &tmp,
                            
&c->x86_capability[cpufeat_word(X86_FEATURE_FSGSBASE)],
-                           &tmp, &tmp);
+                           
&c->x86_capability[cpufeat_word(X86_FEATURE_PREFETCHWT1)],
+                           &tmp);
 }
 
 /*
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4556,10 +4556,15 @@ void hvm_cpuid(unsigned int input, unsig
         if ( vlapic_hw_disabled(vcpu_vlapic(v)) )
             __clear_bit(X86_FEATURE_APIC & 31, edx);
 
-        /* Fix up OSXSAVE. */
-        if ( cpu_has_xsave )
-            *ecx |= (v->arch.hvm_vcpu.guest_cr[4] & X86_CR4_OSXSAVE) ?
-                     cpufeat_mask(X86_FEATURE_OSXSAVE) : 0;
+        /* Fix up XSAVE, OSXSAVE, and AVX. */
+        if ( !cpu_has_xsave )
+            *ecx &= ~cpufeat_mask(X86_FEATURE_XSAVE);
+        if ( !(*ecx & cpufeat_mask(X86_FEATURE_XSAVE)) )
+            *ecx &= ~(cpufeat_mask(X86_FEATURE_OSXSAVE) |
+                      cpufeat_mask(X86_FEATURE_AVX) |
+                      cpufeat_mask(X86_FEATURE_F16C));
+        else if ( v->arch.hvm_vcpu.guest_cr[4] & X86_CR4_OSXSAVE )
+            *ecx |= cpufeat_mask(X86_FEATURE_OSXSAVE);
 
         /* Don't expose PCID to non-hap hvm. */
         if ( !hap_enabled(d) )
@@ -4585,12 +4590,36 @@ void hvm_cpuid(unsigned int input, unsig
         /* Don't expose INVPCID to non-hap hvm. */
         if ( (count == 0) && !hap_enabled(d) )
             *ebx &= ~cpufeat_mask(X86_FEATURE_INVPCID);
+
+        hvm_cpuid(1, NULL, NULL, &_ecx, NULL);
+        if ( !(_ecx & cpufeat_mask(X86_FEATURE_XSAVE)) )
+            *ebx &= ~(cpufeat_mask(X86_FEATURE_AVX2) |
+                      cpufeat_mask(X86_FEATURE_MPX) |
+                      cpufeat_mask(X86_FEATURE_AVX512F));
+        if ( !(*ebx & cpufeat_mask(X86_FEATURE_AVX512F)) )
+        {
+            *ebx &= ~(cpufeat_mask(X86_FEATURE_AVX512DQ) |
+                      cpufeat_mask(X86_FEATURE_AVX512IFMA) |
+                      cpufeat_mask(X86_FEATURE_AVX512PF) |
+                      cpufeat_mask(X86_FEATURE_AVX512ER) |
+                      cpufeat_mask(X86_FEATURE_AVX512CD) |
+                      cpufeat_mask(X86_FEATURE_AVX512BW) |
+                      cpufeat_mask(X86_FEATURE_AVX512VL));
+            *ecx &= ~cpufeat_mask(X86_FEATURE_AVX512VBMI);
+        }
         break;
     case 0xb:
         /* Fix the x2APIC identifier. */
         *edx = v->vcpu_id * 2;
         break;
-    case 0xd:
+
+    case XSTATE_CPUID:
+        hvm_cpuid(1, NULL, NULL, &_ecx, NULL);
+        if ( !(_ecx & cpufeat_mask(X86_FEATURE_XSAVE)) )
+        {
+            *edx = *ecx = *ebx = *eax = 0;
+            break;
+        }
         /* EBX value of main leaf 0 depends on enabled xsave features */
         if ( count == 0 && v->arch.xcr0 ) 
         {
@@ -4637,6 +4666,11 @@ void hvm_cpuid(unsigned int input, unsig
         /* Hide data breakpoint extensions if the hardware has no support. */
         if ( !boot_cpu_has(X86_FEATURE_DBEXT) )
             *ecx &= ~cpufeat_mask(X86_FEATURE_DBEXT);
+        hvm_cpuid(1, NULL, NULL, &_ecx, NULL);
+        if ( !(_ecx & cpufeat_mask(X86_FEATURE_XSAVE)) )
+            *ecx &= ~(cpufeat_mask(X86_FEATURE_XOP) |
+                      cpufeat_mask(X86_FEATURE_LWP) |
+                      cpufeat_mask(X86_FEATURE_FMA4));
         break;
 
     case 0x80000008:
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -11,7 +11,7 @@
 
 #include <xen/const.h>
 
-#define NCAPINTS       8       /* N 32-bit words worth of info */
+#define NCAPINTS       9       /* N 32-bit words worth of info */
 
 /* Intel-defined CPU features, CPUID level 0x00000001 (edx), word 0 */
 #define X86_FEATURE_FPU                (0*32+ 0) /* Onboard FPU */
@@ -159,9 +159,21 @@
 #define X86_FEATURE_NO_FPU_SEL         (7*32+13) /* FPU CS/DS stored as zero */
 #define X86_FEATURE_MPX                (7*32+14) /* Memory Protection 
Extensions */
 #define X86_FEATURE_CAT        (7*32+15) /* Cache Allocation Technology */
+#define X86_FEATURE_AVX512F    (7*32+16) /* AVX-512 instructions */
+#define X86_FEATURE_AVX512DQ   (7*32+17) /* AVX-512 double/quad instructions */
 #define X86_FEATURE_RDSEED     (7*32+18) /* RDSEED instruction */
 #define X86_FEATURE_ADX                (7*32+19) /* ADCX, ADOX instructions */
 #define X86_FEATURE_SMAP       (7*32+20) /* Supervisor Mode Access Prevention 
*/
+#define X86_FEATURE_AVX512IFMA (7*32+21) /* AVX-512 integer FMA instructions */
+#define X86_FEATURE_AVX512PF   (7*32+26) /* AVX-512 prefetch instructions */
+#define X86_FEATURE_AVX512ER   (7*32+27) /* AVX-512 exp/recip instructions */
+#define X86_FEATURE_AVX512CD   (7*32+28) /* AVX-512 conflict detect 
instructions */
+#define X86_FEATURE_AVX512BW   (7*32+30) /* AVX-512 byte/word instructions */
+#define X86_FEATURE_AVX512VL   (7*32+31) /* AVX-512 variable length 
instructions */
+
+/* Intel-defined CPU features, CPUID level 0x00000007:0 (ecx), word 8 */
+#define X86_FEATURE_PREFETCHWT1        (8*32+ 0) /* prefetchwt1 instruction */
+#define X86_FEATURE_AVX512VBMI (8*32+ 1) /* AVX-512 byte manipulate 
instructions */
 
 #define cpufeat_word(idx)      ((idx) / 32)
 #define cpufeat_bit(idx)       ((idx) % 32)

Attachment: x86-HVM-hide-XSAVE-dependents.patch
Description: Text document

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